Vitamin D₃ in fat tissue

The literature describing vitamin D content of fat tissue is extremely limited. We conducted a pilot study that measured the concentrations of vitamin D₃ in the fat tissue and serum of obese adults. These measurements were performed using a new liquid chromatography mass spectrometry (LC/MS) method. The objectives of this study were: to measure and report the vitamin D₃ concentration in serum and subcutaneous fat samples from obese individuals and to examine the association of vitamin D₃ in fat with vitamin D₃ in serum. This cross-sectional study was conducted in 17 obese men and women who were scheduled to undergo gastric bypass surgery. The mean vitamin D₃ concentration in subjects’ subcutaneous fat tissue samples was 102.8 ± 42.0 nmol/kg. The mean vitamin D₃ concentration in serum was 7.78 ± 3.99 nmol/l. Vitamin D₃ concentrations of fat tissue and serum were positively correlated (r = 0.68, P = 0.003). Consistent with previous findings in obese subjects, subjects in this study had suboptimal vitamin D status as demonstrated by a mean 25-hydroxyvitamin D concentration of 43.3 ± 15.4 nmol/l. In conclusion, fat tissue vitamin D₃ can be measured by LC/MS and is detectable in obese subjects with suboptimal vitamin D status. Compatible with the long-standing concept that fat tissue is a storage site for vitamin D, fat tissue and serum vitamin D₃ concentrations were positively correlated.