Hockey stick relationship between 25 OH vitamin D and BMI NHANES

FASEB (Federation of American Societies of Experimental Biology) Journal Vol 24 April 2010 917.10
Lenore Arab1, Heeyoung Kim2 and Alice Ebel3
1 General Internal Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA
2 School of Public Health at UCLA, Los Angeles, CA
3 Humbolt University, Berlin-Kreuzberg, Germany
Circulating levels of vitamin D are shown to be rapidly decreasing in the US population, with up to 90% of the population and more so in the African American population. A negative association between serum levels of 25 OH vitamin D and body mass index levels has also been consistently documented, suggesting that this fat soluble vitamin may be sequestered in adipose tissue.
To examine more closely the true nature of this relationship between body fat and circulating levels of vitamin D we used smoothing methods on NHANES adult Caucasian and African American populations.
These findings suggest that the nature of the relationship is not linear and reflects more closely an inverted hockey stick.
Individuals whose BMIs are under 20 having lower than expected circulating levels of vitamin D, values rise and then fall again among all individuals with a BMI over 20. This is seen in both genders, African Americans and Caucasians.
Among African Americans, the reduction in circulating levels of 25 OH vitamin D per unit of BMI is approximately half that seen in Caucasians.
The race, gender and age adjusted regression coefficients of BMI on vitamin D levels demonstrated an intercept for African Americans of 17.7, and a coefficient of –0.169.
Among Caucasians the comparable values are 37.7 and –0.339, suggesting that among those with the lowest levels of vitamin D, sequestration of vitamin D into adipose tissue is lower.