BioscienceHorizons
Volume 10 2017
10.1093/biohorizons/hzx003
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Research article High salt diets in young university adults and the correlation with blood pressure, protein intake and fat free mass Lim Jia Jiet* and Mitra Soma R. School of Biosciences, University of Nottingham in Malaysia, Semenyih, Malaysia *Corresponding author: School of Biosciences, University of Nottingham in Malaysia, Semenyih, Malaysia. Email:
[email protected] Supervisor: Dr Mitra Soma R., School of Biosciences, University of Nottingham in Malaysia, Semenyih, Malaysia.
................................................................................................................................................................. The diet of young university adults in Malaysia is mainly dependent on the food providers in and around the campus. Limited Malaysian studies have employed 24-h urinary sodium to estimate dietary salt intake in young adults. The fifth National Health and Morbidity Survey (NHMS), Malaysia (2015) concluded that 30.3% of Malaysian adults aged 18 years and above have hypertension. The objective of this study was to investigate the dietary salt intake and blood pressure of young university adults and the relationship between these two variables. This study also estimated the macronutrient content of the foods frequently consumed by the study participants to explore the relationship between the macronutrients, salt and blood pressure. Twenty-eight participants aged between 18 and 25 years old were recruited. Blood pressure was measured using a digital blood pressure monitor. Anthropometric measurements of participants were taken using standard procedures. Twenty-four-hour urinary sodium was analysed using atomic absorption spectrophotometry (AAS). Food intake of the participants was surveyed by an interviewer-administered questionnaire to identify the sources of dietary salt. The mean salt intake of the participants was 10.80 ± 0.78 g/day (ranging from 5.71 g/day to 20.02 g/day), exceeding the recommendation of 5 g/day set by the National Coordinating Committee on Food and Nutrition Malaysia by 116%. The mean systolic blood pressure (SBP) was 104.43 ± 1.68 mmHg, and the mean diastolic blood pressure (DBP) was 66.46 ± 1.23 mmHg. A positive correlation was found between salt intake and SBP, though it was not statistically significant (r = 0.21, p = 0.30). Salt intake was significantly associated with body weight (r = 0.47, p = 0.01), body mass index (BMI) (r = 0.45, p = 0.02) and fat free mass (r = 0.44, p = 0.02); SBP was also significantly correlated with body weight (r = 0.61, p = 0.00), BMI (r = 0.54, p = 0.00) and fat free mass (r = 0.56, p = 0.00). The sodium content of the food products was significantly correlated with energyadjusted protein content of the food (r = 0.67, p = 0.00). Individuals who consumed more than 10 g/day of salt were frequent consumers of ‘dried anchovies/cuttlefish/prawns’, ‘instant meals’, ‘fried rice/noodles’, ‘noodles with soup’ and ‘noodles with soy sauce’. Educating the local food providers to modify their recipes with reduced salt could be part of an integrated strategy to reduce salt intake among the population. Key words: salt intake, blood pressure, urinary sodium, young adults, body composition, Malaysian diet Submitted on 6 July 2016; editorial decision on 31 January 2017
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................................................................................................................................................................. © The Author 2017. Published by Oxford University Press. 1 This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/ licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact
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Introduction Young university adults are experiencing a transition from their family diet to a diet of their own choice. The food habits of young university adults are dependent on and are influenced by the ready-to-eat meals available in and around the university campus. Several studies across the world have shown that individuals who depend on canteen food consume higher salt regardless of them being student or staff (Park et al., 2009; Rasmussen et al., 2010; Ahn et al., 2013). Consumers tend to underestimate the amount of salt in the condiments and seasonings, which are often used to enhance the flavour of food served in canteens. Nevertheless, laboratory methods can be employed to disclose the amount of salt in canteen food. For example, kimchi (a fermented food product) was believed to be the primary source of salt across the Korean population but research revealed that soups and stews were the primary sources of salt in school canteens (Ahn et al., 2013). The average salt content of canteen food in Denmark is 3.4 g per serving, while the average salt content of lunches served at Ghent University is 3.1 g per serving (Rasmussen et al., 2010). Therefore, the high salt content in canteen food needs to be considered in populations that utilize them the most. During the 66th World Health Assembly, the WHO set ‘a 30% relative reduction in mean population intake of salt’ as one of the action plans to prevent and control noncommunicable diseases from 2013 to 2020 (WHO, 2013). High salt intake has been associated with elevated blood pressure in the PURE and INTERSALT studies (Intersalt Coorperative Research Group, 1988; Mente et al., 2014). DASH trials have reported that blood pressure can be reduced significantly by lowering sodium intake from 150 mmol/day to 100 mmol/day and further to 50 mmol/day (Sacks et al., 2001). The prevalence of hypertension has increased globally, rising from approximately 600 million people in 1980 to 1 billion people in 2008 (WHO, 2011). In Malaysia, the National Health and Morbidity Survey (NHMS) 2015 concluded that the prevalence of hypertension in adults is 30.3%, including 17.2% who were previously undiagnosed, suggesting that Malaysians should go for basic health screening (Institute for Public Health, 2015). The United Nations (2015) reported that the life expectancy at birth of Malaysians was 74.5 years between 2010 and 2015; an extrapolation showed that it might achieve 77.0 years between 2025 and 2030. Since age is a non-modifiable risk factor for hypertension, the expenditure on health care will rise without preventive measures in place. Alefan et al. (2009) estimated that the total economic burden for pre-hypertension, Stage 1 hypertension and Stage 2 hypertension was RM9691.08 (2907.32 USD equivalent), RM8396.37 (2518.91 USD equivalent) and RM10229.62 (3068.89 USD equivalent) per person respectively, with at least 73% of the above costs at each level being indirect costs due to productivity loss. Among hypertensive Malaysians, only 8.6% of patients were able to achieve control of their blood pressure (Rampal et al., 2008). Controlling blood pressure in a
Malaysian population at large is difficult due to the inadequate health care services as well as low awareness among Malaysians. Previous studies reported that blood pressure is positively correlated with salt intake (Sacks et al., 2001). In order to estimate dietary salt intake of an individual, 24-h urinary sodium concentration was analysed in our study participants. Twenty-four-hour urinary sodium analysis is the gold standard laboratory technique employed to estimate dietary sodium intake at the individual level (McLean, 2014). About 86–95% of dietary sodium is excreted in urine whereas sweat and faeces account for other losses (Luft, Fineberg and Sloan, 1982; Holbrook et al., 1984). This method is independent of the reliability of food composition tables, an individual’s ability to estimate portion size and an individual’s memory to recall food intake. Since food is prepared in different ways, the use of a food composition table is too general to estimate the dietary salt added to recipes or sauces by the cook, especially when ‘eating-out’ is common among the participants studied. Twenty-four-hour urinary sodium analysis is often used to validate dietary assessment by questionnaires or recall methods and is suitable for all population groups regardless of dietary pattern or food culture, allowing a valid international comparison (McLean, 2014). The relationship between salt and blood pressure is not well studied among young adults and limited studies have employed 24-h urinary sodium to estimate dietary salt intake in Malaysia. Additionally, it is useful to have an overview of the salt intake of young university adults as their diet is mainly dependent on their food providers. The objective of this study was to investigate the salt intake and blood pressure of young university adults and the relationship between the two variables. The energy and protein content of frequently consumed foods were also estimated to determine the relationship between anthropometric and dietary parameters.
Methods Population and study design An observational and cross-sectional study was designed and carried out among the students aged between 18 and 25 years of the University of Nottingham Malaysia Campus. Students who had existing medical complications and smoked regularly were excluded. Participants were recruited by posting flyers on the university information boards and university email system. Some participants were referred by previous participants to join the study. Sample size was calculated to determine the number of participants necessary to obtain the average blood pressure of the population within a 5% error rate with a 95% confidence interval. The formula used was provided by Charan and Biswas (2013):
N=
Z1 − α 2 (SD) 2 , d2
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................................................................................................................................................................. where Z1–α2 = 1.962 (Z1–α = standard normal variate at 5% Type 1 error); SD is the standard deviation of blood pressure obtained from Balami, Salmiah and Nor Afiah (2014) = 12.96; d2 = 52 (d = absolute error or precision). The calculated sample size was 26. Assuming an attrition rate of 20%, an additional six participants were required for this study. Therefore, the planned sample size was 32. The protocol was approved by the University of Nottingham Science & Engineering Research Ethics Committee. Participants were required to sign an informed consent form. Participants were free to withdraw at any point in time during the programme without giving prior notice. No monetary rewards or payments were associated with this programme.
Body composition The weight and height of participants were measured by the researcher and body mass index (BMI) was calculated. The body composition of participants was measured using the direct segmental multi-frequency (20 kHz and 100 kHz) bioelectrical impedance analysis method (DSM-BIA) (InBody230, Seoul Korea). The outcome measures obtained from the InBody analysis included body fat mass, fat free mass and percent body fat.
Blood pressure Given the known day-to-day variation, blood pressure was measured on two different days and the average was calculated and recorded. Participants were allowed to rest for a few minutes after they arrived in the laboratory. Participants were asked to rest their arms at chest level while measurement took place. A digital blood pressure monitor (HL858JA, FOCAL, Japan) was used to measure blood pressure on both the left and right arm and the average was calculated and recorded. Given the diurnal effect of blood pressure, most blood pressure readings were taken in the late afternoon, between 3 and 5 pm. In addition, participants were asked to refrain from consuming stimulants, such as coffee and energy drinks. They were also requested to refrain from eating or exercising at least 2 h prior to the measurement to minimize the transient changes in blood pressure.
24-h urinary sodium A 24-h urine was collected from participants. Participants were given written and verbal instructions on the urine collection procedure based on the WHO/PAHO protocol (WHO/ PAHO, 2010). Participants were encouraged to maintain their usual diet and liquid consumption and refrain from heavy physical activity to minimize sodium loss through sweating. The protocol required the first morning urination to be discarded and the subsequent urination throughout the 24 h was collected in the bottles provided. Upon collection of samples, they were stored in a refrigerator at 15°C prior to analysis. An aliquot of urine was diluted with deionized water at the ratio of 1:5000. The aim of dilution was to enable atomic absorption spectrophotometry
(AAS) to detect sodium in a linear range. The standard curve for sodium is linear for concentrations below 1 mg/L. The technique was calibrated and validated with a known amount of sodium. Each sample was divided into three and was filtered before being subjected to AAS analysis. Sodium concentration was reported in mg/L. The raw data was multiplied by a dilution factor, then multiplied by the volume of 24-h urine output to obtain the amount of sodium excreted in urine per day. Considering that 95% of the sodium consumed is excreted in urine, urinary sodium was multiplied by 100/95 to obtain the dietary sodium (Rashida et al., 2014). Dietary sodium was multiplied by 2.543 to convert dietary sodium to dietary salt (2.543 g of salt contains 1 g of sodium).
Food intake survey A food intake survey was designed to identify the sources of dietary salt. The questionnaire was administered to all participants and was completed by the same researcher. The questionnaire was divided into five sections: (i) The frequency of meal consumption on campus; (ii) The frequency of meal consumption off campus; (iii) The frequency of consuming certain food groups that may be a potential source contributing to dietary salt; (iv) The frequency of consuming certain local dishes that were high in salt; (v) The frequency of preparing their own meals. The food groups listed in the food intake survey were selected from the Nutrient Composition of Malaysian Foods (4th Edition), based on the food groups identified by Choong et al. (2012) as being high in salt and food groups with at least moderate salt content (>100 mg Na/ 100 g). The survey is presented as Fig. 1. The Nutrient Composition of Malaysian Foods (Tee et al., 1997) and the nutrition labels of the food products were used to identify the energy, protein and sodium content of frequently consumed food products that were potential sources of salt (>100 mg Na/100 g). Each food group listed on the questionnaire included a variety of foods from different manufacturers. Average energy, protein and sodium content were calculated and the correlation between these three variables was investigated.
Statistical analysis A normality test was done on all scale data. A log transformation was done on data that were significantly different from normal. Central tendency analysis was performed on all scale data. Data are reported as mean ± standard error of mean throughout this report. An independent t-test was used to compare the differences in variables between males and females; a Pearson’s Correlation analysis was done to investigate the correlations between variables; a one-way ANOVA was used to compare differences in blood pressure between quartiles of dietary salt; a Chi-squared test was used to investigate the differences between salt consumption groups and food intake. Differences were considered significant at p < 0.05. The Statistical Package for Social Sciences (IBM SPSS statistics, version 22) was used for the above analyses.
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Figure 1. The questionnaire used to identify sources of dietary salt.
Results The anthropometric, blood pressure and urinary parameters of study participants are tabulated in Table 1. Study participants with incomplete or contaminated urine sample were requested to recollect their 24-h urine. Out of 32 participants recruited, samples from three participants with incomplete urine and a sample from a participant with contaminated urine were eventually excluded. Therefore, the final data analysis comprised data from 28 participants. Among them, 64% were Malaysian Chinese, 11% were Malaysian Malays while others were Melanau, Siamese, Vietnamese, Indian, British and Iraqi. There was no significant difference in terms of age, BMI, DBP, pulse rate, urine volume or urinary sodium between males and females. However, there was a significant difference in height, weight, PBF, FFM and SBP between the two genders. Only 14% of the participants had a BMI greater than 25.0 kg/ m2 (international cut-off to categorize overweight individuals). The mean SBP and DBP for males and females were within the healthy range (90–120/60–80 mmHg). Urinary sodium was used to assess the dietary salt intake. The mean estimated dietary salt was 10.80 ± 0.78 g after conversion from urinary sodium (175.43 ± 12.65 mmol/day) to dietary salt (Fig. 2). The dietary salt intake of the population ranged from 5.71 g/day to 20.02 g/day. However, the WHO and the National Coordinating Committee on Food and Nutrition (Ministry of Health, 2005) Malaysia recommendation is for less
than 5 g/day of salt. The mean salt intake exceeded the recommendation by 116%. There was no individual with salt intake less than 5 g/day whereas 53.6% of the participants consumed between 5 g/day and 10 g/day of salt. When the data was combined for males and females, the mean SBP was 104.43 ± 1.68 mmHg, ranging from 92 mmHg to 132 mmHg. Most individuals had a SBP lower than 120 mmHg; one individual had an SBP of 132 mmHg, and was categorized as having pre-hypertension. The individual was not aware of his pre-hypertensive condition and was not taking any precautions to control his condition. The mean DBP was 66.46 ± 1.23 mmHg for males and females was combined, ranging from 52 mmHg to 80 mmHg. However, 20% of the individuals had a DBP lower than 60 mmHg. No symptom of low blood pressure was reported although few reported being aware of their low blood pressure status. The correlation of SBP and DBP with dietary salt was not significant (SBP: r = 0.21, p = 0.30; DBP: r = 0.10, p = 0.62) in pooled data. Similarly, the dietary salt was not significantly correlated with SBP and DBP when analysed separately for males (SBP: r = 0.37, p = 0.18; DBP: r = 0.22, p = 0.44) or females (SBP: r = −0.27, p = 0.38; DBP: r = −0.34, p = 0.26). Dietary salt and urine volume were not significantly correlated (r = 0.30, p = 0.12). In the pooled data, dietary salt was significantly associated with anthropometric parameters such as body weight (r = 0.47, p = 0.01), BMI (r = 0.45, p = 0.02)
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................................................................................................................................................................. Table 1. Anthropometric, blood pressure and urinary parameters: differences between genders Male (n = 15)
Female (n = 13)
p-value
Age (years)
21.47 ± 0.48
21.62 ± 0.35
0.96
Height (cm)
172.07 ± 1.40
158.15 ± 0.87
0.00*
Weight (kg)
66.60 ± 3.38
52.42 ± 1.89
0.00*
2
BMI (kg/m )
22.45 ± 1.07
20.93 ± 0.66
0.25
PBF (%)
18.22 ± 2.20
30.22 ± 1.35
0.00*
FM (kg)
12.88 ± 2.30
16.07 ± 1.22
0.25
FFM (kg)
53.72 ± 1.86
36.35 ± 0.86
0.00*
107.74 ± 2.68
100.96 ± 1.45
0.05*
66.10 ± 1.61
66.88 ± 1.96
0.76
Pulse rate (min )
71.47 ± 2.20
73.44 ± 2.28
0.54
Urine volume (L)
1.87 ± 0.21
1.60 ± 0.25
0.42
187.04 ± 16.42
162.03 ± 19.61
0.33
SBP (mmHg) DBP (mmHg) −1
Urinary Na (mmol/day)
The values shown above are mean values ± SEM for male and female participants. Characteristics with significant differences between males and females are marked by asterisk (*), p < 0.05. Significance was determined using independent t-test. PBF: percent body fat; FM: fat mass; FFM: fat free mass; SBP: systolic blood pressure; DBP: diastolic blood pressure.
(r = 0.64, p = 0.01), BMI (r = 0.61, p = 0.02) and FFM (r = 0.68, p = 0.00). Among female participants, dietary salt was not significantly correlated with body weight (r = 0.42, p = 0.15) or BMI (r = 0.40, p = 0.18) but was significantly correlated with FFM (r = 0.60, p = 0.03), whereas SBP was not significantly correlated with anthropometric parameters (body weight: r = 0.15, p = 0.63; BMI: r = 0.17, p = 0.58; FFM: r = −0.09, p = 0.78). Overall, FFM showed a significant correlation with dietary salt and SBP in most cases (Fig. 3). FM and PBF did not have a significant correlation with dietary salt and SBP.
Figure 2. The value in the bar graph is mean ± SE. The vertical bar represents the SE whereas the bold horizontal bar represents the WHO recommendation for salt intake per day (5 g/day).
and FFM (r = 0.44, p = 0.02). Similarly, SBP was also significantly correlated with anthropometric parameters such as body weight (r = 0.61, p = 0.00), BMI (r = 0.54, p = 0.00) and FFM (r = 0.56, p = 0.00). Analysis was also done separately for male and female groups since body weight and FFM differed significantly between groups. Among male participants, dietary salt was not significantly correlated with body weight (r = 0.47, p = 0.08) or BMI (r = 0.46, p = 0.08) but was significantly correlated with FFM (r = 0.52, p = 0.05), whereas SBP was significantly correlated with body weight
The food intake survey showed that 54% of the participants prepared their own meals less than once a week. Only 7% of the participants reported preparing their own meals daily. Among the food groups listed in the food intake survey, the one consumed most frequently among all participants was bakery products, wherein 67.9% of individuals reported having consumed bakery products more than once a week. Individuals who consumed more than 10 g/day of salt were likely to consume ‘instant meals’ and ‘dried anchovies/ cuttlefish/prawns’ more frequently. However, statistical significance was only found for ‘dried anchovies/cuttlefish/prawns’. Moreover, individuals who consumed more than 10 g/day of salt were likely to consume ‘fried rice/noodles’, ‘noodles with soup’ and ‘noodles with soy sauce’ more frequently. However, significance was only found for ‘noodles with soy sauce’. A summary of the differences in the data on the food groups and consumption of dishes between individuals who consumed more than 10 g salt/day and individuals who consumed less than 10 g salt/day is shown in Table 2.
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................................................................................................................................................................. The energy, protein and sodium content of the food groups and dishes listed in the questionnaires are shown in Table 3. Pearson’s Correlation analysis was conducted to investigate the correlation between energy, protein and sodium content of the food groups. Dishes from food outlets were not
included in the analysis as the values for energy-adjusted protein and sodium content were outliers. We found that the sodium content of the food products was significantly correlated with the protein content (r = 0.55, p = 0.00) of the same, as was energy content (r = 0.33, p = 0.04). After
Figure 3. FFM is significantly correlated with salt intake and SBP in most of the cases, except for the correlation of FFM with SBP among females. Data are reported as correlation coefficient (r) with its associated p-value analysed using Pearson’s Correlation. p < 0.05 represents significant association and is marked by an asterisk (*).
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................................................................................................................................................................. controlling for energy, the correlation between sodium content and protein content increased (r = 0.67, p = 0.00) (Fig. 4).
Discussion The current study revealed that the mean estimated dietary salt intake was 10.80 ± 0.78 g, ranging from 5.71 g/day to 20.02 g/ day. Individuals who consumed more than 10 g/day of salt were more likely to consume ‘instant meals’, ‘dried anchovies/ cuttlefish/prawns’ and ‘noodles with soy sauce’. The mean SBP and DBP for males and females were within the healthy range. Overall, FFM showed a significant positive correlation with dietary salt and SBP. The sodium content of food products was significantly correlated with the protein content of the same.
Comparison with other studies The INTERSALT Study found that the average daily urinary sodium excretion of a population generally is between 100 mmol and 200 mmol (Intersalt Coorperative Research Group, 1988). The mean value of the daily urinary sodium (175 mmol) of the participants in the current study falls into this generalization. The Malaysian National Adult Nutrition Survey (MANS) carried out a 24-h food recall on 6886 adults and reported that an average of 6.55 g of salt was consumed by Malaysians daily. Dietary salt intake was positively correlated with higher education; individuals with college or university education consumed the highest amount of salt per day. Malaysian Chinese had a higher daily dietary sodium intake compared to Malaysian Malays and Malaysian Indians. However, the result is not convincing as the study identified that 54% of the participants were ‘under-reporters’ of energy intake (EI), with an EI/BMR ratio of less than 1.2. Since under-reporters were not excluded from the data set, the relatively low-salt intake reported in that study is partly due to under-reporting (Mirnalini et al., 2008). Mirnalini et al. (2008) suggested that the habitual use of soy sauce in cooking contributed to the high salt intake of the Chinese participants. Two Malaysian studies have reported on urinary sodium in the Malaysian population. The PURE study adopted a single fasting morning urine to estimate 24-h urinary sodium for study participants of 18 countries by applying the Kawasaki formula, which yielded a correlation coefficient of 0.71 (CI 95%, 0.65–0.76), when validated within the study (Mente et al., 2014). They estimated the daily urinary sodium excretion of Malaysians to be 164 mmol, close to the value in the current study, which was 175 mmol. In addition to this study, Rashida et al. (2014) carried out a 24-h urinary sodium analysis among 445 normotensive staff of the Ministry of Health Malaysia and reported that the average daily salt intake was 8.0 g/day. However, since the staff in Malaysian government offices are mostly Malaysian Malays, the value is different from the current study in which more than half of the participants were Malaysian Chinese. Mirnalini et al. (2008) reported that Malaysian Chinese and individuals with a
higher education level consumed the highest amount of salt. Hence, it is reasonable that the urinary sodium excretion or estimated dietary salt intake in the current study was higher than in the study carried out by Rashida et al. (2014). The mean SBP and DBP of young adults in a public university in Malaysia as reported by Balami et al. (2014) were 103.45 mmHg and 69.25 mmHg respectively, similar to the findings of the current study. The prevalence of pre-hypertension was 30.1% in their study, in contrast to only one individual being pre-hypertensive in the current study. The low prevalence of pre-hypertension in the current study needs to be interpreted with caution since individuals with existing medical complications were excluded; there were also differences in ethnicity composition between the two studies.
The correlation between salt intake and blood pressure The relationship between salt intake and blood pressure is not straightforward as hypertension is a multifactorial complication. PURE and INTERSALT are two major studies that investigated the relationship between salt intake and blood pressure involving several countries. The PURE study generalized that an increment in 1 g of daily urinary sodium excretion was associated with a 1.45/0.54 mmHg increment in blood pressure (n = 102 216; p < 0.001) (Mente et al., 2014). On the other hand, the INTERSALT study generalized that an increment of 100 mmol of urinary sodium excretion was associated with a 3/0 mmHg increment in blood pressure (n = 10 079; p < 0.01) (Intersalt Cooperative Research Group, 1988). Using these slopes, the association between blood pressure and dietary salt is too subtle to observe; it often requires a large sample size to detect any changes. In the human population, the increment in blood pressure following salt intake differs between individuals as the response of sodium loading to blood pressure is heterogeneous (Luft and Weinberger, 1997). The INTERSALT study is a pooled study that involved 52 study centres around the world, but only 27 centres found a significant positive correlation between urinary sodium and blood pressure. This highlights the difficulties in establishing this relationship between the latter variables. The relationship may be masked by other confounders that are difficult to quantify, such as salt sensitivity, physical activity level, mental stress and other dietary factors (Intersalt Cooperative Research Group, 1988). Frost, Law and Wald (1991) also carried out a pooled analysis on 14 ‘within the population’ studies, where only 6 out of 14 studies had a significant correlation between urinary sodium and blood pressure. In addition, collective analysis demonstrated statistical significance in the relationship between BP and salt intake (n = 12 773; p < 0.001). Frost et al. (1991) suggested that the low correlation between BP and salt intake in their study could be due to the wide range of blood pressure that can be observed at a given urinary sodium excretion and the random error in measuring urinary sodium. This explanation could also hold in the case of the
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................................................................................................................................................................. Table 2. Number and percentage of individuals reporting intake of food from food groups and dishes listed below (at least 3 times per week) Individuals with salt intake < 10 g/day (n = 15)
Individuals with salt intake > 10 g/day (n = 13)
p-value
2 (13.3%)
5 (38.5%)
0.13
11 (73.3%)
6 (46.2%)
0.14
Canned vegetables/beans/peas
2 (13.3%)
0 (0.0%)
0.17
Salted/pickled fruits and vegetables
1 (6.7%)
1 (7.7%)
0.92
Salted egg
0 (0%)
0 (0%)
N/A
Instant meal
1 (6.7%)
4 (30.8%)
0.10
Dried anchovies/cuttlefish/prawns
0 (0%)
3 (23.1%)
0.05*
Canned fish
1 (6.7%)
2 (15.4%)
0.46
Snacks and crackers
5 (33.3%)
4 (30.8%)
0.89
Cheese
1 (6.7%)
2 (15.4%)
0.46
Processed meat
3 (20.0%)
2 (15.4%)
0.75
Fast food
2 (13.3%)
0 (0%)
0.17
Malay style chicken rice
3 (20.0%)
1 (7.7%)
0.35
Biryani rice
2 (13.3%)
0 (0.0%)
0.17
Fried rice/noodles
3 (20.0%)
5 (38.5%)
0.28
Noodles with soup
3 (20.0%)
6 (46.2%)
0.14
Noodles with soy sauce
2 (13.3%)
6 (46.2%)
0.02*
Soup
5 (33.3%)
6 (46.2%)
0.27
Food groups Breakfast cereals Bakery products (breads, buns, puffs, rolls, cakes)
Dishes from food outlets
Data are reported as number of individuals with percentage in parentheses. Groups with significant difference (p < 0.05) is marked by asterisks (*). The p-value is analysed using Chi-squared test. Food groups identified by Choong et al. (2012) as high salt content foods and food groups with at least moderate salt content (>100 mg Na/100 g) from the Nutrient Composition of Malaysian Foods (4th Edition).
current study. Contrary to the studies reported above in which recruited participants were of a wider range of ages, the current study recruited participants between 18 and 25 years old, and it is expected that healthy young adults would have a BP in the healthy range.
The correlation of salt and SBP with anthropometric parameters Several significant associations between anthropometric parameters and SBP were observed in the pooled analysis, but some associations were lost when analysed separately for males and females. The loss of association was probably due to insufficient statistical power for subgroup analysis. The
significant associations observed in the pooled data may also be largely due to the male subgroup, as they had significantly higher body weight, FFM and SBP than females (Table 1). In this study, FFM was significantly correlated with salt and SBP. Limited studies have reported the relationship between FFM and SBP. This finding in the current study is supported by a previous study, which reported that FFM was positively correlated with SBP among a group of active and non-obese young adults (Vaziri et al., 2015). The study population was similar to the current study although physical activity was not assessed in the current study. As most of the females in the current study had low FFM, it was impossible to detect a significant positive correlation for FFM and SBP in female
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................................................................................................................................................................. Table 3. Energy, protein and sodium content of food frequently consumed by the study participants Energy (kcal)
Protein (g)
Sodium (mg)
125
2.2
146
333
4.8
218
150
5.6
252
Tuna-Mayo Sandwich
254
15.0
433
Cream rolls1
182
4.2
151
144
4.0
136
Canned vegetables (asparagus)2
43
4.3
777
Canned baked beans2
96
5.0
365
103
6.6
546
529
15.4
402
50
3.1
2018
–
–
–
Instant porridge1
136
4.1
653
Instant rice vermicelli soup1
412
8.7
1082
Instant noodles1
294
5.7
1161
8
1.8
116
Dried prawns2
23
5.2
255
Dried cuttlefish2
40
8.1
138
Dried salted fish2
46
10.5
433
40
5.2
105
154
19.8
1056
Plain biscuit2
192
4.1
206
Cream crackers2
150
3.0
180
Fish crackers2
167
4.1
241
Food groups (per servings) Breakfast cereals1 Bakery products Oat cookies2 Sliced bread1 2
1
Buns
Canned vegetables/beans/peas
2
Canned processed peas
Salted/pickled fruits and vegetables Salted peas2 Pickled mustard leaves2 Salted egg3 Instant meal
Dried anchovies/cuttlefish/prawns Dried anchovies2
Canned fish Canned sardine2 Canned fish with curry2 Snacks and crackers
Continued
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................................................................................................................................................................. Table 3. Continued
Fish ‘satay’ snack2 2
Prawn crackers Potato chips2
2
Noodle snacks Corn snacks2
Energy (kcal)
Protein (g)
Sodium (mg)
172
6.3
380
106
1.6
187
95
0.9
128
137
3.3
184
91
1.1
127
2
58
3.9
261
Chicken patty2
157
13.7
185
Fish ball2
37
5.7
296
2
225
9.0
634
311
12.0
410
196
11.5
443
Subway sandwich1
384
22.1
911
Pizza2
175
11.5
513
Burger2
364
20.1
697
Malay style chicken rice2
278
16.1
702
Biryani rice2
448
9.6
654
Fried rice2
637
16.2
1465
Fried noodles2
281
9.4
1112
Noodles with soup2
383
20.3
1695
Noodles with soy sauce4
430
20.4
1672
Soup4
197
19.2
1471
Cheddar Cheese Processed meat
Hot dog
Seafood tempura1 1
Chicken nugget Fast food
Dishes from food outlets
Fried rice/noodles
1
Results were the average values of sampled food products based on nutrition labels. Results were taken from the Nutrient Composition of Malaysian Foods. 3 Results were irrelevant because no participant reported consuming salted egg. 4 Results were taken from the Energy & Nutrient Composition of Food, Singapore. 2
participants (Fig. 3). The association of BMI with SBP in the current study was likely to be contributed to by the FFM. Dietary protein contributes to the FFM of an individual. Hence, the correlation between FFM and salt intake in this study suggests that the study participants were consuming a diet high in both protein and salt. This suggestion is supported by the statistically significant positive correlation
between protein and sodium content of frequently consumed foods considered high in salt in our study (Fig. 4). Processed food contributed to the dietary protein in the current study, and such food often contains added sodium. The instant meals and dishes from food outlets, which were good sources of protein, also contributed to the salt in the diets of our participants.
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Figure 4. Energy-adjusted correlation between sodium content and protein content of the frequently consumed food groups (moderate to high salt content) (r = 0.67, p = 0.00).
Sources of sodium in the diet The main source of sodium in the diet differs across populations based on their eating habits (Elliot and Brown, 2007). For example, in China, 76% of dietary sodium comes from the salt added during cooking, whereas in the UK, 95% of the dietary sodium is attributed to processed food intake (Anderson et al., 2010). A study on the Singaporean population, whose dietary pattern is similar to that of the Malaysians, reported that 60% of the dietary sodium was due to the use of salt and salty sauces (Health Promotion Board of Singapore, 2011a). Other sources of sodium included sodium bicarbonate and monosodium glutamate. In the current study, the young university adults depended on the local food providers for their food intake. The consumption of local dishes seems to have contributed to the dietary salt intake, a finding consistent with the claim by the Health Promotion Board of Singapore. As reported in the Nutrient Composition of Malaysian Foods (4th Edition), a typical fried rice contains approximately 3.7 g/serving of salt. Noodles with curry contains approximately 6.2 g/serving. The salt content of dried noodles with chicken and mushrooms is approximately 4.3 g/serving (Tee et al., 1997; Health Promotion Board of Singapore, 2011b). Hence, it is evident that the consumption of one to two servings of these dishes will easily exceed the recommendation of salt intake (5 g/day) by the National Coordinating Committee on Food and Nutrition, Malaysia. Among the Japanese, a population that uses soy sauce extensively in their recipes, soy sauce was estimated to contribute 2 g of the dietary salt intake per person per day (Okuda et al. 2016). Therefore, the Malaysian Chinese must be cautious when adding soy sauce to their recipes.
Awareness of the high salt content in the recipes mentioned in this study is necessary and should be addressed at the local and national level. Publishing articles through local newspapers and magazines as well as broadcasting on Malaysian television channels are several approaches that could be used to promote awareness on the dangers of high salt in the diet, especially the salt in sauces and condiments. Manufacturers of food products should be notified that the salt content in their products is contributing to the disease burden of Malaysia and product reformulation is necessary. A nutrition labelling system such as the ‘traffic-light system’ could be implemented in Malaysia, enabling Malaysians to make informed healthy choices to avoid products with high salt content, which could be highlighted in red on the nutrition labels. The high salt content in dishes prepared by the local food providers needs to be addressed. Recipe reformulation should be suggested, and could involve substituting salt and sauces with herbs and spices to enhance flavour, thus creating a low-salt environment. Furthermore, the outcome of this study could be used to encourage the food outlets on the university campus to reduce the average salt content of meals by 45%, thereby reducing daily salt intake from 10.8 g to 5.9 g in young university adults. The effectiveness of this strategy should be monitored by a follow-up study analysing the salt content of dishes from the food outlets through random food sampling.
Limitations One of the limitations of the current study may be the use of a single 24-h urinary sample as urinary sodium excretion is subject to day-to-day intrapersonal variation. Luft, Fineberg and Sloan (1982) reported that 24-h urinary sodium was not correlated significantly with the mean known sodium intake over 10 days. Increasing the number of 24-h urine collections from an individual could increase the correlational value with other biological measurements such as blood pressure at the individual level (Liu et al., 1979; Luft, Fineberg and Sloan, 1982). Although 24-h urinary sodium is accurate it is susceptible to random error, for instance due to the individual not adhering to their usual diet on the day of urine collection. Luft, Fineberg and Sloan (1982) suggested that nine consecutive 24-h urine collections would be necessary to establish the mean sodium intake of an individual. During the INTERSALT study, only one 24-h urine collection was taken from the participants while only 807 out of 10 079 participants were randomly chosen for a second collection (Intersalt Cooperative Research Group, 1988). Despite understanding the degree of variation, more than one 24-h urine collection was not collected in the current study because that would have increased the burden on the participants regarding urine collection in addition to the time constraints. Nevertheless, participants were encouraged to maintain their usual diet. The survey administered on food intake was not validated due to the time constraint of the study. ‘Food groups’ were listed in the questionnaire rather than individual food items. Hence, the proportional contribution of each food item to the
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................................................................................................................................................................. total dietary salt was not evaluated in the current study. Without a complete and validated food frequency questionnaire, the total energy and protein intake of the study participants were unavailable. Therefore, the association of total protein intake with blood pressure could not be assessed. However, the questionnaire successfully demonstrated the food groups that were the major contributors to the total dietary salt intake in this study. The current study had limited data with respect to subgroup analyses such as males and females and association between SBP and weight-related parameters. Healthy young individuals aged between 18 and 25 years were recruited for the current study, with blood pressure within the healthy range. This limited the ability of the current study to draw an inference on the relationship between salt intake and blood pressure.
Conclusion Salt intake among the young university adults was higher than the recommendation of the Malaysian government and the WHO. The data from the current study adds to existing data on salt intake in the Malaysian population. The mean salt intake of young university adults, of 10.8 g/day, was an alarming finding that requires attention. The current study also suggested that FFM might be related to blood pressure in lean individuals. Further studies are required to demonstrate the impact of protein intake on salt and blood pressure in the young adult population. Since the food intake of young university adults is frequently dependent on their food providers, educating the local food providers to restrict the addition of salt in their recipes must be part of an integrated strategy to reduce salt intake among the population.
Author biography Lim Jia Jiet graduated from University of Nottingham in Malaysia with a First Class Honours Bachelor Degree in Nutrition with particular interest in the relationship between nutrients and diseases. He would like to pursue a Doctoral Degree in the near future. Lim designed this study and it was reviewed and approved by Dr. Mitra. Lim carried out datacollection and urine analyses. Lim performed statistical analyses and had primary responsibility for the final content, assisted by Dr. Mitra.
Acknowledgement We are grateful to our participants for their time and cooperation throughout the duration of the study. Furthermore, we appreciate the help of the laboratory technicians of both the Faculty of Science and the Faculty of Engineering in assisting us with materials and instruments in addition to their guidance.
Funding This study was funded by the School of Biosciences, University of Nottingham in Malaysia.
References Ahn, S., Park, S., Kim, J. N. et al. (2013) Salt content of school meals and comparison of perception related to sodium intake in elementary, middle and high schools, Nutrition Research and Practice, 7 (1), 59–65. Alefan, Q., Ibrahim, M. I., Razak, T. A. et al. (2009) Cost of treating hypertension in Malaysia, Asian Journal of Pharmaceutical and Clinical Research, 2 (1), 1–5. Anderson, C. A. M., Appel, L. J., Okuda, N. et al. (2010) Dietary sources of sodium in China, Japan, the United Kingdom, and the United States, women and men aged 40 to 59 years: the INTERMAP study, Journal of the American Dietetic Association, 110, 736–745. Balami, A. D., Salmiah, M. S. and Nor Afiah, M. Z. (2014) Association of behavioural factors, body mass index status, family history of hypertension and prehypertension among a Public University Students in Malaysia, International Journal of Public Health and Clinical Sciences, 1 (2), 109–120. Charan, J. and Biswas, T. (2013) How to calculate sample size for different study designs in medical research? Indian Journal of Psychological Medicine, 35 (2), 121–126. Choong, S. S., Balan, S. N., Chua, L. et al. (2012) Preference and intake frequency of high sodium foods and dishes and their correlations with anthropometric measurements among Malaysian subjects, Nutrition Research and Practice, 6 (3), 238–245. Elliot, P. and Brown, I. (2007) Sodium Intakes around the World, WHO Press, Switzerland. Frost, C. D., Law, M. R. and Wald, N. J. (1991) By how much does dietary salt reduction lower blood pressure? II-analysis of observational data within populations, BMJ (Clinical Research ed.), 302, 815–818. Health Promotion Board of Singapore. (2011a) HPB Declares War on Salt: Singapore Residents Exceed Daily Recommended Salt by 60%. [ONLINE] accessed at: http://www.worldactiononsalt.com/worldact ion/asia/53960.html (18 April 2016). Health Promotion Board of Singapore. (2011b) Energy & Nutrient Composition of Food. [ONLINE] accessed at: http://focos.hpb.gov.sg/ eservices/ENCF/foodsearch.aspx (14 March 2016). Holbrook, J. T., Patterson, K. Y., Bodner, J. E. et al. (1984) Sodium and potassium intake and balance in adults consuming self-selected diets, The American Journal of Clinical Nutrition, 40, 786–793. Intersalt Cooperative Research Group. (1988) Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion, British Medical Journal, 297, 319–328.
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Research article
................................................................................................................................................................. Institute for Public Health. (2015) National Health and Morbidity Survey 2015. [ONLINE] accessed at: http://www.iku.gov.my/images/IKU/ Document/REPORT/nhmsreport2015vol2.pdf (26 June 2016). Liu, K., Cooper, R., McKeever, J. et al. (1979) Assessment of the association between habitual salt intake and blood pressure: methodological problems, American Journal of Epidemiology, 110 (2), 219–226. Luft, F. C., Fineberg, N. S. and Sloan, R. S. (1982) Estimating dietary sodium intake in individuals receiving a randomly fluctuating intake, Hypertension, 4, 805–808. Luft, F. C. and Weinberger, M. H. (1997) Heterogeneous responses to changes in dietary salt intake: the salt-sensitivity paradigm, American Journal of Clinical Nutrition, 65 (suppl), 612S–617S. McLean, R. M. (2014) Measuring population sodium intake: a review of methods, Nutrients, 6, 4651–4662. Mente, A., O’Donnell, M. J., Rangarajan, S. et al. (2014) Association of urinary sodium and potassium excretion with blood pressure, The New England Journal of Medicine, 371 (7), 601–611. Ministry of Health. (2005) Recommended Nutrient Intakes for Malaysia, Ministry of Health Malaysia, Putrajaya. Mirnalini, K., Zalilah, M. S., Safiah, M. Y. et al. (2008) Energy and nutrient intakes: findings from the Malaysian Adult Nutrition Survey (MANS), Malaysian Journal of Nutrition, 14 (1), 1–24. Okuda, N., Okayama, A., Miura, K. et al. (2016) Food sources of dietary sodium in Japanese adult population in the international study of macro-/micronutrients and blood pressure (INTERMAP), European Journal of Nutrition, 2016. doi: http://dx.doi.org/10.1007/ s00394-016-1177-1. Park, H., Jeong, G., Lee, S. et al. (2009) Workers intake too much salt from dishes eating out and food service cafeterias; direct chemical analysis of sodium content, Nutrition Research and Practice, 3 (4), 328–333. Rampal, L., Rampal, S., Azhar, M. Z. et al. (2008) Prevalence, awareness, treatment and control of hypertension in Malaysia: a national study
of 16,440 subjects, Journal of the Royal Institute of Public Health, 122, 11–18. Rasmussen, L. B., Lassen, A. D., Hansen, K. et al. (2010) Salt content in canteen and fast food meals in Denmark, Food & Nutrition Research, 54. DOI:10.3402/fnr.v54i0.2100. Rashida, A., Yeo, P. S., Noor Ani, A. et al. (2014) Sodium intake among normotensive health staff assessed by 24-hour urinary excretion: a cross-sectional study, Malaysian Journal of Nutrition, 20 (3), 317–326. Sacks, F. M., Svetkey, L. P., Vollmer, W. M. et al. (2001) Effects on blood pressure of reduced dietary sodium and the dietary approaches to stop hypertension (DASH) diet, The New England Journal of Medicine, 344 (1), 3–10. Tee, E. S., Mohd Ismail, N., Mohd Nasir, A. et al. (1997) Nutrient Composition of Malaysian Foods, 4th edn, Institute of Medical Research, Kuala Lumpur. United Nations. (2015) World Population Prospects: The 2015 Revision. [ONLINE] accessed at: https://esa.un.org/unpd/wpp/publications/ files/key_findings_wpp_2015.pdf (27 January 2017). Vaziri, Y., Bulduk, S., Shadman, Z. et al. (2015) Lean body mass as a predictive value of hypertension in young adults, in Ankara, Turkey, Iran, Journal of Public Health, 44 (12), 1643–1654. WHO. (2011) Global Status Report on Noncommunicable Diseases 2010, World Health Organization, Geneva. WHO. (2013) Follow-up to the Political Declaration of the High-level Meeting of the General Assembly on the Prevention and Control of Non-communicable Diseases. [ONLINE] accessed at: http:// apps.who.int/gb/ebwha/pdf_files/WHA66/A66_R10-en.pdf (30 March 2016). WHO/PAHO. (2010) Protocol for Population Level Sodium Determination in 24-Hour Urine Samples. [ONLINE] accessed at: http://www.paho. org/hq/index.php?option=com_docman&task=doc_view&gid= 21488&Itemid (16 September 2015).
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