Relationship between physical activity, physical performance, and iron

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Relationship between physical activity, physical performance, and iron status in adult women

Appl. Physiol. Nutr. Metab. Downloaded from www.nrcresearchpress.com by Cornell University on 05/21/13 For personal use only.

Scott E. Crouter, Diane M. DellaValle, and Jere D. Haas

Abstract: Iron deficiency affects approximately 16% of US females 18–45 years old. Iron is a key component of hemecontaining proteins, which are essential for oxygen transport throughout the body. With low iron levels, performance and intense physical activity may be compromised. Thus, the purpose of this study was to examine the relationship between iron status, physical performance, and physical activity in 18- to 45-year-old females. Participants (N = 109) were screened for iron status using a venous blood sample, had their height and mass measured, and self-reported their physical activity level. The screening was used to match iron-depleted nonanemic females (hemoglobin, Hgb > 120 g·L–1; serum ferritin, sFer < 20 µg·L–1) to females with normal iron levels. After participant matching, they had their body composition measured, performed three cycle ergometer tests (maximal, endurance, and efficiency), and wore an ActiGraph GT1M accelerometer for five consecutive days, except when sleeping or during water activities. The final sample consisted of 25 iron-depleted participants and 24 with normal iron levels. Key findings were as follows: (i) after controlling for fat-free mass and vigorous _ 2 at ventilatory threshold compared with those with norphysical activity, iron-depleted females had a significantly lower VO mal iron levels (P < 0.05); and (ii) after controlling for age, iron-depleted females spent significantly more time in sedentary behaviors and significantly less time in light physical activity than those with normal iron levels (P < 0.05). The increased sedentary time in iron-depleted females may contribute to excess mass gain over time; however, further investigation is needed to confirm these results. Key words: maximal aerobic capacity, iron depletion, accelerometry, endurance, efficiency, hemoglobin. Résumé : Environ 16 % des femmes âgées de 18 à 45 ans aux États-Unis sont carencées en fer. Le fer est un élément essentiel des protéines renfermant un hème servant au transport de l’indispensable oxygène dans tout l’organisme. Quand le fer est en faible quantité, la performance et l’activité intense sont compromises. Cette étude se propose d’analyser la relation entre le bilan ferrique, la performance physique et l’activité physique chez des femmes âgées de 18 à 45 ans. Après avoir sélectionné des participantes (N = 109) sur la base de leur bilan en fer mesuré à partir d’un échantillon de sang veineux, on évalue leur stature et leur masse corporelle et on les questionne sur leur degré de pratique de l’activité physique. La sélection des participantes sert à apparier des femmes vidées de leur fer, mais non anémiques (hémoglobine, Hgb > 120 g·L–1; ferritine sérique, sFer < 20 µg·L–1) à des femmes présentant un niveau de fer normal. Suite à l’appariement des femmes, on évalue leur composition corporelle, leur rendement à trois tests sur un ergocycle (maximal, endurance, rendement) et on leur demande de porter un accéléromètre de marque ActiGraph GT1M durant cinq jours sauf pendant le sommeil et les activités aquatiques. L’échantillon final comprend 25 participantes vidées de leur fer et 24 femmes présentant un niveau de fer normal. Les principaux résultats sont (i) après la prise en compte de la masse maigre et de l’activité physique vigoureuse, _ 2 significativement plus faible que les femmes présentant un niles femmes vidées de leur fer ont au seuil ventilatoire un VO veau de fer normal (P < 0,05), et (ii) après la prise en compte de l’âge, les femmes vidées de leur fer consacrent significativement plus de temps à des activités sédentaires et moins de temps à des activités physiques d’intensité légère que les femmes présentant un niveau de fer normal (P < 0,05). Le surplus de temps que les femmes vidées de leur fer consacrent à des activités sédentaires pourrait contribuer à la trop grande prise de poids au fil du temps; néanmoins, d’autres études doivent ratifier ces observations. Mots‐clés : capacité aérobie, déplétion du fer, accélérométrie, endurance, rendement, hémoglobine. [Traduit par la Rédaction]

Received 15 December 2011. Accepted 28 February 2012. Published at www.nrcresearchpress.com/apnm on 24 May 2012. S.E. Crouter.* Cornell University, Division of Nutritional Sciences, Ithaca, NY 14853, USA. D.M. DellaValle. Cornell University, USDA/ARS, Robert W. Holley Center for Agriculture and Health, Ithaca, NY 14853, USA. J.D. Haas. Cornell University, Division of Nutritional Sciences, 220 Savage Hall, Ithaca, NY 14853, USA. Corresponding author: Scott E. Crouter (e-mail: [email protected]). *Present address: University of Massachusetts Boston, Department of Exercise and Health Sciences, 100 Morrissey Boulevard, Boston, MA 02125, USA. Appl. Physiol. Nutr. Metab. 37: 697–705 (2012)

doi:10.1139/H2012-044

Published by NRC Research Press

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Introduction Iron deficiency is the most prevalent micronutrient deficiency throughout the world. It is estimated that the prevalence of iron deficiency, based on serum ferritin (sFer) < 12 µg·L–1, in US males and females, 18–45 years of age, is approximately 3%–4% and 12%–16%, respectively (Cogswell et al. 2009; Looker et al. 1997; Centers for Disease Control and Prevention (CDC) 2002). In the most severe cases, irondeficiency anemia, which is defined by a low hemoglobin level (Hgb), it is estimated that the prevalence in US females 12–49 years of age is approximately 5% (Cogswell et al. 2009). Iron deficiency affects the body because of its key role in heme-containing proteins. Hgb in the blood plays an essential part in transferring oxygen from the lungs to the body tissues. Myoglobin transports and stores oxygen and releases it to meet increased metabolic needs during muscle contraction. Cytochromes are critical to respiration and energy metabolism within the mitochondrial electron transport chain. Numerous studies have shown that iron-deficiency anemia has negative impacts on physical performance and work capacity (Haas 2006; Haas and Brownlie 2001). For example, iron-deficiency anemia is associated with reductions in oxygen carrying capacity, which impairs maximal and submaximal aerobic capacity (Brownlie et al. 2002). However, not as well understood is the impact of iron deficiency without anemia and the level of iron deficiency needed to impact physical performance and work capacity. For example, in a review of relevant literature, Haas and Brownlie (2001) concluded that iron deficiency without anemia is associated with reductions in tissue oxidative capacity, which impairs endurance and energetic efficiency. Traditionally, a sFer value of 6 mg·L–1 were defined as abnormal and were excluded from additional participation in the study. Thirty participants were found to be irondepleted nonanemic, and 69 participants were found to have normal iron levels. Ten participants with hemoglobin of 0.05).

Discussion The primary aim of this study was to examine the relationship between daily physical activity, physical performance, and iron status in a diverse group of females with varying physical activity levels. The main findings from the current study were that the iron-depleted participants had a significantly lower VT and spent significantly more time in sedentary behaviors and significantly less time in LPA than those participants with normal iron levels. Relationship between iron status and physical performance Consistent with most previous work, we did not see a difference between the iron status groups for maximal aerobic capacity (Haas 2006; Hinton et al. 2000; Zhu and Haas 1997, 1998). It has generally been shown that only those Published by NRC Research Press

Crouter et al.

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Table 1. Physical characteristics, hematological measures, physical performance factors, and accelerometer-measured physical activity of the female participants (mean ± standard deviation). Range is shown in parenthesis for the physical characteristics and hematological measures. Measure Age (years) Height (cm) Mass (kg) BMI (kg·m–2) Body fat (%) Fat mass (kg) Fat-free mass (kg) Hgb (g·L–1) sFer (µg·L–1) sTfR (µg·mL–1) Fe (µg·dL–1) TIBC (µg·dL–1) TS (%) Body iron (mg·kg–1) Maximal exercise test V_ O2peak (L·min–1) V_ O2peak (mL·kg–1·min–1) Maximal watts Maximal heart rate (bpm) Ventilatory threshold (VT) V_ O2 at VT (L·min–1) V_ O2 at VT (% of V_ O2peak) Watts at VT Heart rate at VT (bpm) Endurance testing Workload (watts) Average V_ O2 (L·min–1) Average RER Average heart rate (bpm) Endurance ride time (min) Efficiency testing Gross efficiency (%) Net efficiency (%) Delta efficiency (%) Physical activity Sedentary behaviors (min·day–1) LPA (min·day–1) MPA (min·day–1) VPA (min·day–1) MVPA (min·day–1)

Iron depleted (N = 25; SF < 20 µg·L–1) 30±9.8 (18–45) 166.9±4.6 (159–176) 63.1±11.5 (51.7–98.0) 22.5±3.8 (18.5–34.1) 27.6±8.5 (17.7–45.3) 18.1±9.2 (9.4–44.6) 45.0±4.7 (35.3–53.9) 130±9.1 (121–149) 11.4±5.6 (2.0–19.2) 6.6±2.4 (3.7–16.2) 62.2±40.8 (4.7–182.0) 375.3±64.4 (278.0–516.0) 17.6±12.8 (1.0–52.2) 0.04±3.22 (–9.0–4.0)

Normal iron level (N = 24; SF ≥ 20 µg·L–1) 30±8.6 (19–43) 165.0±5.6 (159–176) 60.3±7.2 (50.8–77.6) 22.1±2.1 (17.4–34.0) 26.1±6.4 (15.5–37.4) 15.9±4.7 (7.6–24.9) 44.4±5.4 (35.0–60.1) 132.8±6.9 (124–150) 42.2±16.9 (21.3–83.3) 4.9±1.2 (3.0–8.0) 101.9±36.2 (48.0–193.0) 325.2±48.7 (246.0–418.9) 31.9±11.9 (12.4–63.7) 6.16±1.67 (3.0–9.0)

2.12±0.46 34.6±8.8 190±36.9 175±10.5

2.15±0.60 35.6±9.0 196±46.0 177±9.8

0.874 0.691 0.610 0.412

1.34±0.33 63.8±9.8 110±31.2 134±16.9

1.44±0.40 67.3±5.5 118±34.7 137±14.6

0.370 0.136 0.452 0.471

139±31.6 1.8±0.38 1.01±0.05 157±13.8 14.5±9.5

141±44.0 1.8±0.48 0.99±0.05 161±11.9 15.5±9.7

0.832 0.915 0.204 0.255 0.714

20.4±1.4 26.1±1.7 32.9±2.2

20.4±2.2 25.9±2.2 33.0±4.7

0.905 0.798 0.917

524.5±133.1 290.1±98.0 127.6±45.9 16.9±17.1 144.5±49.3

457.8±74.8 340.8±53.0 124.4±39.5 13.2±12.1 137.5±45.6

0.038 0.031 0.795 0.383 0.612

P value 0.994 0.198 0.353 0.639 0.510 0.310 0.664 0.207