BACKGROUND: Vitamin D plays pleiotropic roles in the body and hence, changes in its metabolism and distribution during starvation could play an important role in the adaptive response to famine. We aimed to identify the responses of some vitamin D metabolites to 8 d of fasting and exercise. METHODS: A repeated-measures design was implemented, in which 14 male volunteers fasted for 8 d and performed an exercise test before and after fasting. Serum samples were collected on day 1 after night fasting and after 8 d of complete food restriction, before and 1 h and 3 h after exercise. RESULTS: After 8 d of fasting, compared with baseline values, serum 24,25(OH)2D3 and 3-epi-25(OH)D3 levels significantly increased; those of 25(OH)D3 and 1,25(OH)2D3 were unaffected; and those of 25(OH)D2 decreased. Exercise on the first day of fasting induced an increase in serum 3-epi-25(OH)D3 levels, while exercise performed after 8 d of fasting induced an increase in 25(OH)D3, 24,25(OH)2D3, 25(OH)D2, and 3-epi-25(OH)D3 levels. CONCLUSION: Increases in 24,25(OH)2D3 and 3-epi-25(OH)D3 levels imply that fasting stimulates vitamin D metabolism. The effects of exercise on serum vitamin D metabolites, which are most pronounced after fasting and in subjects with serum 25(OH)D3 above 25 ng/mL, support the notion that fasting and exercise augment vitamin D metabolism.
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