Topical Area: Vitamins and Minerals
Objectives : Vitamin D deficiency is often observed in obese person. One of the mechanisms suggested is the decreased bioavailability of vitamin D due to its deposition in adipose tissue. We investigated the effects of obesity on vitamin D distribution by measuring 25(OH)D levels in circulation and comparing vitamin D content in liver and adipose tissue from obese and control mice fed different levels of vitamin D.
Methods : Six-wk-old C57BL/6 mice were fed control or high fat (10 or 45% kcal fat, CON or HFD) diets containing different levels of vitamin D3 (1,000, or 25,000 IU/kg of diet, CVd or HVd) for 13 wks. Serum 25-hydroxyvitamin D (25(OH)D) level was determined by radioimmunoassay. Vitamin D3 and 25(OH)D3 levels in the liver and epididymal adipose tissue (AT) were quantified by LC-MS/MS. mRNA levels of liver Cyp2r1 and Cyp27a1 were determined by real-time PCR.
Results : Overall, serum 25(OH)D levels were significantly higher in the HVd groups compared with CVd groups. There was no difference in serum 25(OH)D levels between CON-CVd and HFD-CVd groups. However, in the vitamin D supplemented groups, HFD-HVd group had significantly lower serum 25(OH)D levels (20% lower) than CON-HVd group. Vitamin D3 levels in the liver and AT were 55 and 100 times higher in the HVd groups (liver and AT: 719 and 318 ng/g tissue) compared with the CVd groups. 25(OH)D3 levels in the liver and AT were also 3.3 and 2.4 times higher in the HVd groups (liver and AT: 33.9 and 18.9 ng/g tissue) than those of the CVd groups. Total amount of vitamin D3 in the liver and AT were significantly higher in the HFD-HVd group (121 and 44% higher) compared with CON-HVd group. However, when mice were fed the control levels of vitamin D, dietary fat levels did not affect the vitamin D3 amount in the liver and AT. Liver Cyp2r1 and Cyp27a1 mRNA levels did not differ among groups.
Conclusions : When vitamin D intake was at a supplementation level, a significant amount of dietary vitamin D seemed to be stored in the liver and AT; thus excess body adiposity could contribute to lower serum 25(OH)D level. However, at a control level of vitamin D intake, obesity did not affect tissue vitamin D amount and serum 25(OH)D levels.
Funding Sources : Supported by the grant from the National Research Foundation (NRF) of Korea (NRF-2018R1D1A1B070491) and Research Grant from Research Affairs at Seoul National University.