Abstract
BackgroundVitamin D insufficiency (serum 25-OH vitamin D > 10 ng/ml and < 30 ng/ml) is prevalent in the obese (body mass index (BMI) > 30 kg/m2), yet relationships between the two are poorly understood. Objectives of this study include identification of the impact of obesity on reducing serum 25-OH vitamin D concentration, particularly in response to altered vitamin D3 supplementation, and to elucidate the longitudinal impact of serum 25-OH vitamin D on body mass index.MethodsTwenty four-week-old lean and obese male C57BL/6 J mice were fed low, standard, or high levels of cholecalciferol supplementation and followed for 24 weeks. Longitudinal measurements include serum 25-OH and 1,25-(OH)2 vitamin D, intact PTH, and calcium concentrations, as well as BMI, bone density and body fat/lean mass.ResultsBaseline serum 25-OH concentrations were not different in lean and obese mice (lean 32.8 ± 4.4 ng/ml versus obese 30.9 ± 1.6 ng/ml p = 0.09). Lean mice receiving low supplementation exhibited rapid declines in serum 25-OH vitamin D concentrations, falling from 33.4 ± 5.4 ng/ml to 14.5 ± 3.4 ng/ml after 2 weeks, while obese mice declined at a lower rate, falling from 30.9 ± 1.5 to 19.0 ± 0.9 ng/ml within the same time period. Surprisingly, high vitamin D3 supplementation did not substantially increase serum vitamin D concentrations above standard supplementation, in either lean or obese mice. No differences in serum 1,25-(OH)2 vitamin D, intact parathyroid hormone (PTH) or serum calcium were observed between lean and obese mice within the same vitamin D supplementation group. Yet obese mice exhibited lower serum calcitriol, higher serum PTH, and lower bone mineral density (BMD) than did lean mice. Additionally, neither body mass index nor body fat % was significantly correlated with vitamin D concentrations. Interestingly, lean mice with high vitamin D supplementation consumed significantly more food than did lean mice with standard or low supplementation (14.6 ± 1.7 kcal/mouse/day versus 11.8 ± 1.4 and 12.3 ± 1.7 respectively, p < 0.0001 for both).ConclusionsLow cholecalciferol supplementation in both lean and obese mice significantly and sustainably reduces serum 25-OH vitamin D concentrations. Interestingly, obesity slowed the rate of decline. Over the period of the study, vitamin D insufficiency was not subsequently correlated with greater BMI/body fat, although lean mice with high supplementation consumed greater calories with no apparent BMI increase.
Highlights
Vitamin D insufficiency is prevalent in the obese (body mass index (BMI) > 30 kg/m2), yet relationships between the two are poorly understood
Several human studies have explored the possibility that these two phenomena may be linked [3,4,5,6], it remains unclear if vitamin D insufficiency promotes weight gain and/or if obesity modulates serum vitamin D concentration
Serum 25-OH vitamin D concentrations fall rapidly with low supplementation to a constant insufficient level, while greater supplementation leads to little increase; obesity tempers decline in response to low vitamin D chow In order to understand the varied interrelationships between vitamin D and body weight/composition, we set out to establish a range of serum 25-OH vitamin D concentrations between insufficiency (>10 ng/ml) and above sufficiency (>30 ng/ml) in lean and obese mice
Summary
Vitamin D insufficiency (serum 25-OH vitamin D > 10 ng/ml and < 30 ng/ml) is prevalent in the obese (body mass index (BMI) > 30 kg/m2), yet relationships between the two are poorly understood. Several human studies have explored the possibility that these two phenomena may be linked [3,4,5,6], it remains unclear if vitamin D insufficiency promotes weight gain and/or if obesity modulates serum vitamin D concentration. Over-expression of VDR in adipocytes induced weight gain in mice [15]. Interpretation of these data suggests that vitamin D, through VDR, increases weight gain, other studies have shown that administration of 1,25-(OH) vitamin D, the active form of vitamin D and direct ligand to VDR, decreases weight and has other beneficial effects [16, 17]
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