International Journal of Sport Nutrition and Exercise Metabolism, 2015, 25, 128 -135 http://dx.doi.org/10.1123/ijsnem.2013-0250 © 2014 Human Kinetics, Inc.
www.IJSNEM-Journal.com ORIGINAL RESEARCH
Relation Between Vitamin D Status and Body Composition in Collegiate Athletes Jenna E. Heller, Joi J. Thomas, Bruce W. Hollis, and D. Enette Larson-Meyer Excess body fat or obesity is known to increase risk of poor vitamin D status in nonathletes but it is not known if this is the case in athletes. Furthermore, the reason for this association is not understood, but is thought to be due to either sequestration of the fat-soluble vitamin within adipose tissue or the effect of volume dilution related to obese individuals’ larger body size. Forty two US college athletes (24 men 18 women, 20.7 ± 1.6 years, 85.0 ± 28.7 kg, BMI = 25.7 ± 6.1 kg/m2) provided blood samples during the fall and underwent measurement of body composition via dual energy X-ray absorptiometry. Serum samples were evaluated for 25-hydroxyvitamin D (25(OH)D) concentration to assess vitamin D status using Diasorin 25(OH)D radioiodine assay. Serum 25(OH)D concentration was negatively associated with height (r = –0.45), total body mass (r = –0.57), BMI (r = –0.57), body fat percentage (r = –0.45), fat mass (r = –0.60) and fat-free mass (r = –0.51) (p < .05). These associations did not change after controlling for sex. In a linear regression mixed model, fat mass (coefficient -0.47, p = .01), but not fat-free mass (coefficient -0.18, p = .32) significantly predicted vitamin D status and explained approximately 36% of the variation in serum 25(OH)D concentration. These results suggest that athletes with a large body size and/or excess adiposity may be at higher risk for vitamin D insufficiency and deficiency. In addition, the significant association between serum 25(OH)D concentration and fat mass in the mixed model, which remained after controlling for sex, is in support of vitamin D sequestration rather than volume dilution as an explanation for such association. Keywords: athletes, fat mass, fat-free mass, 25(OH) D, fat sequestration, clinical assessment Vitamin D plays a role in many physiological processes and health conditions (Cannell et al., 2008; Holick, 2007). Many of these are particularly relevant to athletes and include bone health, immune modulation and muscle strength, function and power (Larson-Meyer & Willis, 2010). In athletes and nonathletes, low vitamin D status increases risk of stress fracture (Lappe et al., 2008; Ruohola et al., 2006) and respiratory and other acute infections (Halliday et al., 2011; Laaksi et al., 2007; Sabetta et al., 2010), and delays recovery following orthopedic surgery (Barker et al., 2011). Previous studies have found that many athletes have insufficient vitamin D intake (Halliday et al., 2011; Willis et al. 2008) and/or exhibit low serum 25(OH)D concentrations indicative of vitamin D insufficiency (25(OH)D < 32 ng/ml) or deficiency (25(OH)D < 20 ng/ml) (Bescos Garcia & Rodriguez Guisado, 2011; Constantini et al., 2010; Hamilton et al. 2010; Storlie et al., 2011; Willis et al., 2012). While vitamin D status is dependent on both dietary intake and cutaneous synthesis from sun expoHeller and Larson-Meyer are with the Dept. of Family and Consumer Sciences, and Thomas the Athletics Dept., University of Wyoming, Laramie, WY. Hollis is with the Medical University of South Carolina, Charleston, SC. Address author correspondence to D. Enette Larson-Meyer at [email protected].
128
sure, endogenous synthesis is thought to have the most influence on status (Holick, 2007; Holick et al., 2007). In athletes, synthesis of vitamin D is largely dependent on training location, time and season of training, skin pigmentation, and clothing worn outdoors, as well as numerous individual and environmental factors (LarsonMeyer & Willis, 2010). Athletes who train primarily indoors, or outdoors at high latitudes (>32 degrees north or south) (Hollis, 2005; Larson-Meyer & Willis, 2010), very early or late in the day, when the sun is not at an optimal zenith angle for vitamin D synthesis (Hamilton et al., 2010; Willis et al., 2012), or with limited skin exposed (due to clothing worn or sunscreen use) may be at increased risk of insufficiency and deficiency. Excess body fat or obesity is also found to increase risk of low vitamin D status in nonathletes (Arunabh et al., 2003; Drincic et al., 2012; Liel et al., 1988; Looker, 2005; Vimaleswaran et al., 2013; Wortsman et al., 2000). Although the underlying explanation and direction of causality are unclear (Earthman, Beckman, Masodkar, & Sibley, 2012), the majority of available evidence suggests that obesity causes or contributes to low vitamin D status rather than vice versa (Gallagher et al., 2013; Sneve et al., 2008; Vimaleswaran et al., 2013). While various mechanisms have been proposed to explain this association, including those related to insufficient skin exposure to sunlight due to the social stigma of obesity
Vitamin D and Body Fat 129
and impaired cutaneous synthesis due to excess adiposity (Vimaleswaran et al., 2013), the most widely accepted hypothesis is that the fat-soluble vitamin becomes “sequestered” or tightly bound within subcutaneous fat in the obese (Liel et al., 1988; Wortsman et al., 2000). Studies in the early seventies demonstrated that vitamin D accumulates in adipose tissue after injection of radioactive D3 (Mawer et al., 1972) and is found readily on analysis (Rosenstreich et al., 1971). From their studies in normal weight and obese individuals and isolated skin tissue, Wortsman and colleagues (Wortsman et al., 2000) found that obesity does not affect the capacity of skin to produce vitamin D3,. A recent study by Drincic and colleagues (Drincic et al., 2012), however, has challenged the “fat sequestration” hypothesis and proposed that the association between obesity/body size, and vitamin D concentration is a result of volume dilution due to the overall larger body size of overweight and obese individuals. It is still unknown whether adiposity should be taken into consideration while assessing vitamin D requirements in athletes. Athletes in general have a lower range of body fat than nonathletes and have more lean (or fat-free mass) and less body fat for a given body mass or body volume. The purpose of this study was to evaluate the association between vitamin D status and body size and composition in male and female college athletes participating in a variety of sports and determine whether such an association is sex dependent (i.e., beyond the expected differences in body fat between men and women). A secondary purpose was to delineate in an athletic population the factors most responsible for the purported association, fat sequestration or volume dilution. The results of this study will provide insights as to whether larger or more obese athletes are at risk for vitamin D insufficiency/ deficiency and need higher than usual doses of vitamin D for supplementation.
Methods Subjects Men and women NCAA Division 1 athletes from the University of Wyoming (UW) were invited to participate in our ongoing studies evaluating the vitamin D status of athletes. This cross-sectional analysis was performed in 42 athletes during the 2009–2012 academic years. To be included in the current analysis, athletes had to have both measurement of vitamin D status in the fall and body composition assessed by Dual energy x-ray absorptiometry (DXA) in the same academic year, and be free from injury which precluded regular training with their respective team. The study was approved by both the UW Institutional Review Board and the UW Athletics Department. Athletes provided written informed consent before participation. All athletes had undergone a routine preseason physical with the UW Athletics Department team physician and were considered to be in good health for sports participation. Participating athletes were active in American football, basketball, track and field, cross-
country, swimming, wrestling, basketball, soccer, and cheerleading. Athletes in football, track and field, and cross country practiced outdoors from 3 to 5 p.m., those in soccer practiced outdoors from 4 to 6 p.m. while those in basketball, swimming, wrestling and cheerleading/dance practiced indoors. Athletes were not excluded based on vitamin D supplementation or tanning bed use, however, none regularly took vitamin D supplements in an amount >800 IU and none reported using tanning beds.
Overview of Testing Athletes had blood drawn in the fall (at a single point during August through mid-October). Fall semester was selected because cutaneous vitamin D synthesis is possible during these months at our latitude (41.3° N), and preliminary studies suggest there may be no association between vitamin D status and body size/composition in winter months (Halliday et al., 2011; Willis et al., 2008) when endogenous synthesis is not possible. Vitamin D status was categorized according to previously defined criteria (Halliday et al., 2011; Willis et al., 2008) such that deficient status is defined as 25(OH)D concentration< 20 ng/ml; insufficient is defined as 25(OH)D concentration .05). As shown in Table 2, five athletes (11.9%) were found to be vitamin D-deficient, six (14.3%) were vitamin D-insufficient, six (14.3%) had sufficient status, and 25 (59.5%) had optimal status. Women appeared to be less likely to have insufficient or deficient status, and more likely to have optimal status. Body mass and BMI did not change from the fall vitamin D assessment draw (68.7 ± 16.6 kg, BMI-22.2 ± 3.5 kg/m2) to the spring body composition testing (68.7 ± 15.4 kg, BMI-22.4 ± 3.4 kg/m2) in the athletes (n = 28) who had these measures separated by more
Table 1 Descriptive Characteristics of Study Participants Height (cm) Weight (kg)
Males (n = 24)
Females (n = 18)
179.7 ± 11.0
187.0 ± 7.0
170.0 ± 7.2**
85.0 ± 28.7
103.0 ± 24.9
61.1 ± 9.1**
25.7 ± 6.1
29.2 ± 5.7
21.1 ± 2.0**
Fat Free Mass (kg)
62.1 ± 1.8
75.2 ± 11.8
44.7 ± 4.8**
Fat Mass (kg)
18.7 ± 10.4
22.4 ± 11.7
13.7 ± 5.6**
Body fat (percent)
21.9 ± 6.6
21.2 ± 7.8
22.9 ± 4.7
Body mass index
(kg/m2)
Total (n = 42)
PTH (ng/L)*
25.4 ± 11.0
22.6 ± 7.9
29.6 ± 13.7**
25(OH)D (ng/ml)
40.5 ± 15.2
36.1 ± 14.9
46.3 ± 13.9
Note. Data are presented as Mean ± SD. * n = 40, 24 male and 16 female participants due to missing data in 2 female participants; PTH, parathyroid hormone. **significantly different between male and female athletes, p < .05
Table 2 Vitamin D Status in Male and Female Athletes Status
Serum 25(OH)D
Total (n = 42)
Male Athletes (n = 24)
Female Athletes (n = 18)
Deficient
www.IJSNEM-Journal.com ORIGINAL RESEARCH
Relation Between Vitamin D Status and Body Composition in Collegiate Athletes Jenna E. Heller, Joi J. Thomas, Bruce W. Hollis, and D. Enette Larson-Meyer Excess body fat or obesity is known to increase risk of poor vitamin D status in nonathletes but it is not known if this is the case in athletes. Furthermore, the reason for this association is not understood, but is thought to be due to either sequestration of the fat-soluble vitamin within adipose tissue or the effect of volume dilution related to obese individuals’ larger body size. Forty two US college athletes (24 men 18 women, 20.7 ± 1.6 years, 85.0 ± 28.7 kg, BMI = 25.7 ± 6.1 kg/m2) provided blood samples during the fall and underwent measurement of body composition via dual energy X-ray absorptiometry. Serum samples were evaluated for 25-hydroxyvitamin D (25(OH)D) concentration to assess vitamin D status using Diasorin 25(OH)D radioiodine assay. Serum 25(OH)D concentration was negatively associated with height (r = –0.45), total body mass (r = –0.57), BMI (r = –0.57), body fat percentage (r = –0.45), fat mass (r = –0.60) and fat-free mass (r = –0.51) (p < .05). These associations did not change after controlling for sex. In a linear regression mixed model, fat mass (coefficient -0.47, p = .01), but not fat-free mass (coefficient -0.18, p = .32) significantly predicted vitamin D status and explained approximately 36% of the variation in serum 25(OH)D concentration. These results suggest that athletes with a large body size and/or excess adiposity may be at higher risk for vitamin D insufficiency and deficiency. In addition, the significant association between serum 25(OH)D concentration and fat mass in the mixed model, which remained after controlling for sex, is in support of vitamin D sequestration rather than volume dilution as an explanation for such association. Keywords: athletes, fat mass, fat-free mass, 25(OH) D, fat sequestration, clinical assessment Vitamin D plays a role in many physiological processes and health conditions (Cannell et al., 2008; Holick, 2007). Many of these are particularly relevant to athletes and include bone health, immune modulation and muscle strength, function and power (Larson-Meyer & Willis, 2010). In athletes and nonathletes, low vitamin D status increases risk of stress fracture (Lappe et al., 2008; Ruohola et al., 2006) and respiratory and other acute infections (Halliday et al., 2011; Laaksi et al., 2007; Sabetta et al., 2010), and delays recovery following orthopedic surgery (Barker et al., 2011). Previous studies have found that many athletes have insufficient vitamin D intake (Halliday et al., 2011; Willis et al. 2008) and/or exhibit low serum 25(OH)D concentrations indicative of vitamin D insufficiency (25(OH)D < 32 ng/ml) or deficiency (25(OH)D < 20 ng/ml) (Bescos Garcia & Rodriguez Guisado, 2011; Constantini et al., 2010; Hamilton et al. 2010; Storlie et al., 2011; Willis et al., 2012). While vitamin D status is dependent on both dietary intake and cutaneous synthesis from sun expoHeller and Larson-Meyer are with the Dept. of Family and Consumer Sciences, and Thomas the Athletics Dept., University of Wyoming, Laramie, WY. Hollis is with the Medical University of South Carolina, Charleston, SC. Address author correspondence to D. Enette Larson-Meyer at [email protected].
128
sure, endogenous synthesis is thought to have the most influence on status (Holick, 2007; Holick et al., 2007). In athletes, synthesis of vitamin D is largely dependent on training location, time and season of training, skin pigmentation, and clothing worn outdoors, as well as numerous individual and environmental factors (LarsonMeyer & Willis, 2010). Athletes who train primarily indoors, or outdoors at high latitudes (>32 degrees north or south) (Hollis, 2005; Larson-Meyer & Willis, 2010), very early or late in the day, when the sun is not at an optimal zenith angle for vitamin D synthesis (Hamilton et al., 2010; Willis et al., 2012), or with limited skin exposed (due to clothing worn or sunscreen use) may be at increased risk of insufficiency and deficiency. Excess body fat or obesity is also found to increase risk of low vitamin D status in nonathletes (Arunabh et al., 2003; Drincic et al., 2012; Liel et al., 1988; Looker, 2005; Vimaleswaran et al., 2013; Wortsman et al., 2000). Although the underlying explanation and direction of causality are unclear (Earthman, Beckman, Masodkar, & Sibley, 2012), the majority of available evidence suggests that obesity causes or contributes to low vitamin D status rather than vice versa (Gallagher et al., 2013; Sneve et al., 2008; Vimaleswaran et al., 2013). While various mechanisms have been proposed to explain this association, including those related to insufficient skin exposure to sunlight due to the social stigma of obesity
Vitamin D and Body Fat 129
and impaired cutaneous synthesis due to excess adiposity (Vimaleswaran et al., 2013), the most widely accepted hypothesis is that the fat-soluble vitamin becomes “sequestered” or tightly bound within subcutaneous fat in the obese (Liel et al., 1988; Wortsman et al., 2000). Studies in the early seventies demonstrated that vitamin D accumulates in adipose tissue after injection of radioactive D3 (Mawer et al., 1972) and is found readily on analysis (Rosenstreich et al., 1971). From their studies in normal weight and obese individuals and isolated skin tissue, Wortsman and colleagues (Wortsman et al., 2000) found that obesity does not affect the capacity of skin to produce vitamin D3,. A recent study by Drincic and colleagues (Drincic et al., 2012), however, has challenged the “fat sequestration” hypothesis and proposed that the association between obesity/body size, and vitamin D concentration is a result of volume dilution due to the overall larger body size of overweight and obese individuals. It is still unknown whether adiposity should be taken into consideration while assessing vitamin D requirements in athletes. Athletes in general have a lower range of body fat than nonathletes and have more lean (or fat-free mass) and less body fat for a given body mass or body volume. The purpose of this study was to evaluate the association between vitamin D status and body size and composition in male and female college athletes participating in a variety of sports and determine whether such an association is sex dependent (i.e., beyond the expected differences in body fat between men and women). A secondary purpose was to delineate in an athletic population the factors most responsible for the purported association, fat sequestration or volume dilution. The results of this study will provide insights as to whether larger or more obese athletes are at risk for vitamin D insufficiency/ deficiency and need higher than usual doses of vitamin D for supplementation.
Methods Subjects Men and women NCAA Division 1 athletes from the University of Wyoming (UW) were invited to participate in our ongoing studies evaluating the vitamin D status of athletes. This cross-sectional analysis was performed in 42 athletes during the 2009–2012 academic years. To be included in the current analysis, athletes had to have both measurement of vitamin D status in the fall and body composition assessed by Dual energy x-ray absorptiometry (DXA) in the same academic year, and be free from injury which precluded regular training with their respective team. The study was approved by both the UW Institutional Review Board and the UW Athletics Department. Athletes provided written informed consent before participation. All athletes had undergone a routine preseason physical with the UW Athletics Department team physician and were considered to be in good health for sports participation. Participating athletes were active in American football, basketball, track and field, cross-
country, swimming, wrestling, basketball, soccer, and cheerleading. Athletes in football, track and field, and cross country practiced outdoors from 3 to 5 p.m., those in soccer practiced outdoors from 4 to 6 p.m. while those in basketball, swimming, wrestling and cheerleading/dance practiced indoors. Athletes were not excluded based on vitamin D supplementation or tanning bed use, however, none regularly took vitamin D supplements in an amount >800 IU and none reported using tanning beds.
Overview of Testing Athletes had blood drawn in the fall (at a single point during August through mid-October). Fall semester was selected because cutaneous vitamin D synthesis is possible during these months at our latitude (41.3° N), and preliminary studies suggest there may be no association between vitamin D status and body size/composition in winter months (Halliday et al., 2011; Willis et al., 2008) when endogenous synthesis is not possible. Vitamin D status was categorized according to previously defined criteria (Halliday et al., 2011; Willis et al., 2008) such that deficient status is defined as 25(OH)D concentration< 20 ng/ml; insufficient is defined as 25(OH)D concentration .05). As shown in Table 2, five athletes (11.9%) were found to be vitamin D-deficient, six (14.3%) were vitamin D-insufficient, six (14.3%) had sufficient status, and 25 (59.5%) had optimal status. Women appeared to be less likely to have insufficient or deficient status, and more likely to have optimal status. Body mass and BMI did not change from the fall vitamin D assessment draw (68.7 ± 16.6 kg, BMI-22.2 ± 3.5 kg/m2) to the spring body composition testing (68.7 ± 15.4 kg, BMI-22.4 ± 3.4 kg/m2) in the athletes (n = 28) who had these measures separated by more
Table 1 Descriptive Characteristics of Study Participants Height (cm) Weight (kg)
Males (n = 24)
Females (n = 18)
179.7 ± 11.0
187.0 ± 7.0
170.0 ± 7.2**
85.0 ± 28.7
103.0 ± 24.9
61.1 ± 9.1**
25.7 ± 6.1
29.2 ± 5.7
21.1 ± 2.0**
Fat Free Mass (kg)
62.1 ± 1.8
75.2 ± 11.8
44.7 ± 4.8**
Fat Mass (kg)
18.7 ± 10.4
22.4 ± 11.7
13.7 ± 5.6**
Body fat (percent)
21.9 ± 6.6
21.2 ± 7.8
22.9 ± 4.7
Body mass index
(kg/m2)
Total (n = 42)
PTH (ng/L)*
25.4 ± 11.0
22.6 ± 7.9
29.6 ± 13.7**
25(OH)D (ng/ml)
40.5 ± 15.2
36.1 ± 14.9
46.3 ± 13.9
Note. Data are presented as Mean ± SD. * n = 40, 24 male and 16 female participants due to missing data in 2 female participants; PTH, parathyroid hormone. **significantly different between male and female athletes, p < .05
Table 2 Vitamin D Status in Male and Female Athletes Status
Serum 25(OH)D
Total (n = 42)
Male Athletes (n = 24)
Female Athletes (n = 18)
Deficient
