Walter Blackwell, BS, Michael Crossey, MD, and Robert H. Glew, PhD. Albuquerque, New Mexico ..... ME, Olson JA, Shike M, Ross AC, eds. Modern Nutrition in ...
FOLATE AND VITAMIN B12 STATUS OF ADOLESCENT GIRLS IN NORTHERN NIGERIA Dorothy J. VanderJagt, PhD, Kevin Spelman, BA, Joseph Ambe, MD, Pradip Datta, PhD, Walter Blackwell, BS, Michael Crossey, MD, and Robert H. Glew, PhD Albuquerque, New Mexico, Maiduguri, Nigeria, and Tarrytown, New York
The diets of populations in many developing countries are low in folate and vitamin B12 and a deficiency of either of these vitamins results in increased risk for cardiovascular disease and neural tube defects. The rates of neural tube defects in Nigeria are among the highest reported worldwide. Since many girls marry at an early age in northern Nigeria, we therefore determined the folate and vitamin B12 status of adolescent girls between 12 and 16 years of age in Maiduguri, Nigeria. The mean serum folate concentration for subjects was 15.3 + 5.2 nmol/L. Whereas only four subjects (2.4%) had serum folate concentrations lower than 6.8 nmol/l, a level indicative of negative folate balance, 9% of the subjects had serum vitamin B12 concentrations at or below 1 34 pmol/L, the lower limit of the reference range for their age group. Serum homocysteine was measured in 56 of the 162 subjects and the mean level was 15.9 + 5.0 ,umol/L. The majority of subjects had serum homocysteine concentrations above the upper limit of the reference range for their age group. We conclude that the adolescent girls we studied were at greater risk for vitamin B12 deficiency than folate deficiency. This conclusion is consistent with the fact that their diet included few foods that contained vitamin B1 2. J Natl Med Assoc. 2000;92:334-340.)
Keywords: folate * vitamin B12 * homocysteine* adolescent girls * Nigeria The diets in many developing countries, including tlhose of populations in stub-Saharan Africa, are based mainly on cereals and are often limited in the amouints of green leafy vegetables and meat and © 2000. From the Departments of Biochemistry and Molecular Biology and of Pathology, University of New Mexico School of Medicine, Albuquerque, NM; the Department of Paediatrics, University of Maiduguri Teaching Hospital, Maiduguri, Borno State, Nigeria; Bayer Corporation, Diagnostics Division, Tarrytown, NY; and Tricore Reference Laboratory, Albuquerque, NM. Requests for reprints should be addressed to Robert H. Glew, PhD, Department of Biochemistry and Molecular Biology, University of New Mexico School of Medicine, Room 249, BMSB, Albuquerque, NM 87131. 334
dairy products they contain. These foods are rich in folate or vitamin B12. Both of these vitamins are essential for human health, and requirements for folate and vitamin B12 increase during periods of rapid growth and developinent stuch as inifancy, adolescence, and pregnancy.' Folate is required for one-carbon transfer reactions involved in DNA synthesis and amino acid metabolism.2 Vitamin B12, which is found almost exclutsively in foods of animal origin, is necessary for the assimilation- of branchedchain and odd-chain fatty acids." A deficiency of either folate or vitamin B1, affects maturation of red blood cells and compromises immmune function.il-'3 Folate and vitamin B1I2 both participate in the conversion of homocysteine to methionine, such that a deficiency of either vitamin will result in elevated serum concentrations of homocysteine , JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION
FOLATE AND VITAMIN B 2 IN NIGERIAN ADOLESCENTS
whlichi is an indlependent risk factor for cardiovasctular disease8' as well as neural tube defects.1I lI The incidence of neutral ttube (lef'ects varies amlonig popuilationis and is related to socioeconomic status, genetic factors, and diff'erences in maternal folate and vitamin-n B1, status.'2''` The U.S. Ptublic Health Service recoimnmenids that women of childbearing age consuime 400 pug of folic acidl per day.' 4 In the U.S., between 1983 and 1990, the incidence of spina bifida, one of the most common forms of neural tuLbe defects, was 4.6 per 10,000 births.' 5 In Australia, the incidence of neural ttube defects is reported to be 20 per 10,000 births."l' HowNev-er, in less developed couintries, wvhere the intake of folate-rich foods may be limited, the rates of these birth defects are likely to be even higher. In fact, a retrospective analysis of the records of 19,094 deliveries of infants born betwveen 1991 and 1992 in Accra, Ghlanla, showved the rate of neural ttube defects to be 11.5 per 1(0,000 births. '7 The highest rate of neural tube defects was reported for a 3-year prospective study condtucted at a lhospital in central Nigeria, Nwhere the incidence of neural tube defects was estiimiated to be 70 per 10,000 births.'8 According to customn and tradition, in many parts of sub-Saharan Africa, girls as youLng as 12 to 15 years of age are eligible f'or marriage upon finishing seconda-ry school and may becomue pregnanit 1 to 2 years later. Adolescents are at risk for variouts ntutritional deficiencies, particularly folate deficiencV,19- 2 because of their rapid rate of' growth during this period of developmtient. The goal of the present sttudy was to determine the folate and vitainini BI., status of a representative group of teenage girls in Maiduguiri, Nigeria, a region of' the cotuntry Nwhere the incidence of netural tube defects is thouglht to be high.
METHODS
ported in the frozeni state to Albtuquterqtue, NM. Weights and heights were recorded f'or each subject, and the body mass index (BMI) was calculated (kg/ In 2). Information regarding the current vitamin supplement use by the stubjects Nwas also recorded. No hemiatological indices were obtained for the subjects. This study was approved by the Human Research Review Committee of the University of New Mexico Health Scieinces Center, and informed consent was obtained fromn each participant.
School Meals Although dietary inforimation wvas not obtained for individual subjects, a description of the typical meals served at the schools was obtained. During the wveek, sttudents wvere served three meals per day at the school wvith the option of purchasing snacks from the Honme Economiiics Department dturing reguilar school hoturs.
Serum Folate Analysis The concenitration of serunii folate was determined using the ACS:180 folate assay rtun on the randomn-access, fully automiated ACS: 180 immunoassay system (Chiron Diagnostics, East Walpole, MA). The analyzer was calibrated using a two-point calibration algorithm. The coefficient of variation (CV) for the method at low folate concentrations (2.3 ng/mL) wNtas 8.3%, and the CV at higher folate levels (15.6 ng/mnL) was 3.8%.
Serum Vitamin B12 Analysis Serum vitamin B 12 wvas determiined using the ACS:180 VB12, a chemiluminescent assay, run on the automated random-access ACS: 180 analyzer. Sample concentrations of' vitamin B19) were calculated using a stored six-point master curve and a two-point calibration algorithm.
Subjects
Serum Homocysteine Analysis
Adolescent girls betwveen 12 and 16 years of age were recruited fi-om the students attending Governmenit Secondary Schools in Maiduguri, Nigeria. Blood samples wvere obtained by veniptincture and collected into evacuiated tuibes. The samples wvere kept on ice and wvere centrifuiged at 1200 X g for 10 inin wvithin 1 h of collectioni to minimize the transfer of homiocysteine fromi the red cells into the serum.n"' Aliqutots of' sertunm (1 mL) wvere transferred to cryovials anid stored at -200C until they were trans-
Homocvsteine exists in serum as a combination of various free and protein-bound forms and is Usually reported as total homnocvsteine (tHys)."2 The tHvs concentration in the serum samples was determinied using the Imx homocysteine system (Avis Biochemicals, Oslo, Norway), a fluorescence polarization immunoassay (FPIA). The mlx homnocysteine assay utilizes a fotur-parameter logistic curve reduction to generate a calibration curve. Samples of' processed human serum, containing specified
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FOLATE AND VITAMIN B12 IN NIGERIAN ADOLESCENTS
Table 1. Summary of Study Population Characteristics Age (yr)
Height (cm) Weight (kg) BMI (kg/M2) Supplement use None
Daily Weekly Monthly
Mean ± SD (n = 162) 13.5 1.2 153 + 7.8 40.7 ± 8.1 17.1 ± 2.6
40 30S
I-*
119 2 31 10
..
I
36
20
-
LI.
15
-
0
5
amounts of i,-homocysteine provided by the manufacturer, were used as controls. The CV for the assay was 5.2% a 5.9 ,umol/liter and 3.7% at 21.6 ,umol/ liter.
Statistical Analysis Descriptive statistics and regression analysis were performed using the Number Cruncher Statistical System (NCSS 2000, Kaysville, UT). All nonlinear variables were normalized by an appropriate transformation before statistical analysis. Serum vitamin B12 and folate concentrations were normalized using a log transformation, and serum homocysteine concentrations were normalized by a reciprocal transformation. A p value of 0.05 or less was considered statistically significant.
RESULTS Summary of the Characteristics of the Subjects A summary of the characteristics of subjects who participated in this study (n = 162) is presented in Table 1. Their mean age was 13.5 ± 1.2 years and their mean weights and heights were 40.7 ± 8.1 kg and 153.4 ± 7.8 cm, respectively. Their calculated BMI values ranged from 10.5 to 26.9 kg/mi2, with a mean of 17.2 + 2.6 kg/m2. Of the total study population consisting of 162 subjects, only 43 reported using either a folate or multivitamin supplement. Only two subjects took supplements daily, whereas 31 reported they were taking supplements once a week. Ten reported taking a supplement about once a month.
Serum Folate Levels The distribution of serum folate concentrations is shown in Figure 1. The mean serum folate concentration for the study population was 15.3 ± 5.2 336
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10
15
20
25
30
Serum folate (nmol/L) Figure 1. The distribution of serum folate concentrations in adolescent girls in Maiduguri, Nigeria. The solid line above the distribution indicates the reference range for females in that age group. nmol/liter, ranging from 5.07 to 30.1 nmol/liter (Table 2). Four subjects (2.4%) had serum folate concentrations lower than 6.8 nmol/liter, which is the level considered indicative of early negative folate balance.23 The majority of the subjects had serum folate concentrations within the normal range for their age group (Figure 1) .24
Serum B12 Concentrations The serum vitamin B12 levels in this population ranged from 94 to 519 pmol/liter, with a mean of 224 ± 81.6 pmol/liter. Approximately 9% of the subjects (13 of 141) for whom serum vitamin B12 analyses were performed had serum vitamin B12 concentrations below 134 pmol/liter, which is the lower limit of the reference range for females in their age range.24 However, the serum vitamin B12 concentrations were not normally distributed and were skewed toward the lower end of the reference range (Figure 2); furthermore, the median vitamin B12 value was 205 pmol/liter, which is slightly above the lower limit of the normal range.
Serum Homocysteine Concentrations Because of limited sample volume, the concentration of serum homocysteine could be determined for only 56 of the 162 subjects. The serum homocysteine concentrations of these individuals ranged from 8.3 to 35.6 ,umol/liter, with a mean of 15.9 ± 5.0 ,umol/liter. Only three subjects (5.3%) had a serum homocysteine concentration that was VOL. 92, NO. 7, JULY 2000
FOLATE AND VITAMIN B12 IN NIGERIAN ADOLESCENTS
Table 2. Summary of Serum Biochemical Measurements
Folate (nmol/liter) Vitamin B1 2 (pmol/liter)
Homocysteine (ttmol/liter)
Mean ± SD 1 5.3 ±- 5.2 224 ± 82 15.9 ± 5.0
n 162 141 56
Reference range* 6.1-36.8 134-605 4.7-10.3
*Soldin et al.24 70
35
60 -1
30
50
2520
-
20
10
-
10
5
=
c
40
e
30_
U.
-
-I
-
I
_
0
0 95
180 265 350 430 515 Serum vitamin B12 (pmol/L)
2
8
14
20
26
Serum homocysteine
32
38
(gmolIL)
Figure 2. The distribution of serum vitamin B12 concentrations in adolescent girls in Maiduguri, Nigeria. The solid line above the distribution indicates the reference range for females in that age group.
Figure 3. The distribution of serum homocysteine concentrations in adolescent girls in Maiduguri, Nigeria. The solid line above the distribution indicates the reference range for females in that age group.
within the reference range for females in their age range.24 The majority of serum homocysteine concentrations (94.7%) were above 10.3 ,umol/liter (Figure 3), the level which is assumed to be indicative of moderate hyperhomocysteinemia.83 Over the concentration ranges of serum folate and vitamin B12 observed for the subjects in this study, no significant correlations with serum homocysteine concentrations were obtained.
drink), sobo (red sorrel drink), groundnuts, fried yams, and dried fish. On a 100-g basis, the folate content of the foods was estimnated to range from 16 ,ug for yams to 75 jig for groundnuts (USDA Nutrient Data Laboratory).
Folate and B12 Content of Typical Meals Consumed by Subjects on a Daily Basis The subjects routinely consumed porridge for breakfast, which consisted of a mixture of rice and millet. Soup, prepared from either sorghum or baobab leaves (kuka in Hausa) and accompanied by rice and beans, was the usual lunch meal. Dinner was similar to lunch. The snacks that were available for purchase from the Home Economics Department during school hours included moimoi (bean product), massa (rice and cassava), kunu (a millet JOURNAL OF THE NATIONAL MEDICAL ASSOCIATION
DISCUSSION One of the two main findings of the present study is that, based on serum folate concentrations, the folate status of adolescent girls in northern Nigeria appears to be satisfactory. Only 2% of the subjects in our study had serum folate concentrations indicative of early negative folate balance (
