# Presentation: 521160

## Anne C. Looker, Ph.D. 

**Do body fat and exercise modulate vitamin D status?**

## 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?

## Serum 25OHD* by body fatness quartile	

**Non-Hispanic white females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean

- **estimated from bioelectrical impedance

## 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

## 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?

## Serum 25OHD* by physical activity

**Serum 25OHD* by physical activity**

**Non-Hispanic white females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean

**Selected activities quartiles**
** ****(times/month)**

**Activity compared**
**to peers**

## 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

## Percent body fat* by physical activity

**Percent body fat* by physical activity**

**Non-Hispanic white females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean, estimated from bioelectrical impedance

**Selected activities quartiles**
** ****(times/month)**

**Activity compared**
**to peers**

- p= 0.0000

- p= 0.0000

## Serum 25OHD* by selected activities 

**Serum 25OHD* by selected activities **

**Non-Hispanic white females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean

**Quartile, times/month****  **

**Percent body fat**

- p= 0.0000

- p= 0.0000

## 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?**

## Serum 25OHD* by  % body fat** quartile	

**Serum 25OHD* by  % body fat** quartile****	**

**Non-Hispanic females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean

- **estimated from bioelectrical impedance

- p interaction = 0.000

## Serum 25OHD* by selected activities	

**Serum 25OHD* by selected activities****	**

**Non-Hispanic females age 20-49 y**

- SOURCE: NHANES III 1988-94

- *Age-adjusted mean

- p interaction = 0.000

**Quartile, times/month****  **

## Contributing factors?

- Differences in skin synthesis of vitamin D
- Differences in distribution of subcutaneous fat

## Age-adjusted skinfold ratios

**Age-adjusted skinfold ratios**

**Non-Hispanics age 20+ with healthy weight***

- SOURCE: NHANES III

***BMI 18-24.9; **p<0.05**

- **

- **

- **

## Conclusions

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