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Anne C. Looker, Ph.D.

Do body fat and exercise modulate vitamin D status?. Anne C. Looker, Ph.D. . Objectives. What is the relationship between body fat or body mass index (BMI) and serum 25-hydroxyvitamin D (25OHD)? What is the relationship between physical activity and 25OHD?

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Anne C. Looker, Ph.D.

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  1. Do body fat and exercise modulate vitamin D status? Anne C. Looker, Ph.D.

  2. Objectives • What is the relationship between body fat or body mass index (BMI) and serum 25-hydroxyvitamin D (25OHD)? • What is the relationship between physical activity and 25OHD? • Do these relationships vary by race?

  3. Q1 Q2 Q3 Q4 ng/mL 50 p= 0.000 p= 0.000 40 30 20 10 0 % body fat** BMI Serum 25OHD* by body fatness quartile Non-Hispanic white females age 20-49 y *Age-adjusted mean **estimated from bioelectrical impedance SOURCE: NHANES III 1988-94

  4. Possible mechanisms • Decreased sun exposure due to limited mobility or avoidance of outdoor activity • Negative feedback from higher 1,25(OH)2D on hepatic synthesis of 25OHD • Adipose tissue effects

  5. Objectives • What is the relationship between body fat or body mass index (BMI) and serum 25-hydroxyvitamin D ( 25OHD )? • What is the relationship between physical activity and 25OHD? • Do these relationships vary by race?

  6. p= 0.0000 p= 0.0005 0-1 2-9 10-29 30+ Less Same More Serum 25OHD* by physical activity Non-Hispanic white females age 20-49 y ng/mL Selected activities quartiles (times/month) Activity compared to peers *Age-adjusted mean SOURCE: NHANES III 1988-94

  7. Possible mechanisms • Direct effect of physical activity on 25OHD metabolism • Confounding due to relationship between sun exposure and physical activity • Confounding due to relationship between body fat and physical activity

  8. 50 40 30 20 10 0 0-1 2-9 10-29 30+ Less Same More Percent body fat* by physical activity Non-Hispanic white females age 20-49 y Percent p= 0.0000 p= 0.0000 Selected activities quartiles (times/month) Activity compared to peers *Age-adjusted mean, estimated from bioelectrical impedance SOURCE: NHANES III 1988-94

  9. 50 Q1 Q2 Q3 Q4 40 30 20 10 0 Not adjusted Adjusted Serum 25OHD* by selected activities Non-Hispanic white females age 20-49 y Quartile, times/month ng/mL p= 0.0000 p= 0.0000 Percent body fat *Age-adjusted mean SOURCE: NHANES III 1988-94

  10. Objectives • What is the relationship between body fat or body mass index (BMI) and serum 25-hydroxyvitamin D ( 25OHD )? • What is the relationship between physical activity and 25OHD? • Do these relationships vary by race?

  11. Q1 Q2 Q3 Q4 50 40 30 20 10 0 White Black Serum 25OHD* by % body fat** quartile Non-Hispanic females age 20-49 y ng/mL p interaction = 0.000 *Age-adjusted mean **estimated from bioelectrical impedance SOURCE: NHANES III 1988-94

  12. Q1 Q2 Q3 Q4 50 40 30 20 10 0 White Black Serum 25OHD* by selected activities Non-Hispanic females age 20-49 y Quartile, times/month ng/mL p interaction = 0.000 *Age-adjusted mean SOURCE: NHANES III 1988-94

  13. Contributing factors? • Differences in skin synthesis of vitamin D • Differences in distribution of subcutaneous fat

  14. White Black 6 5 4 3 2 1 0 Men Men Women Women Thigh/Subscapular Triceps/Subscapular Age-adjusted skinfold ratios Non-Hispanics age 20+ with healthy weight* Ratio ** ** ** *BMI 18-24.9; **p<0.05 SOURCE: NHANES III

  15. Conclusions • Relationships between 25OHD and body fat or physical activity: • Complex • Appear to vary by race • More research needed to determine basis of complexity

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