The mechanism responsible for the decrease in vitamin D status (i.e., plasma or serum 25-hydroxyvitamin D (25(OH)D) concentration) during inflammatory stress is unknown in humans. Interferon (IFN)-γ is an inflammatory cytokine that regulates vitamin D metabolism in isolated immune cells, but data suggesting this regulation exists in vivo is lacking. The purpose of this study, therefore, was to associate circulating IFN-γ perturbations with 25(OH)D and 1,25-dihydroxyvitamin D (1,25(OH)D) alterations during inflammatory stress in young adults recovering from anterior cruciate ligament (ACL) reconstruction. Plasma 25(OH)D, 1,25(OH)D and IFN-γ concentrations were measured in fasting blood draw samples obtained from twelve-male patients pre-surgery and 90-m, 3-d and 7-d post-surgery. 25(OH)D decreased significantly (p<0.05) after surgery, and strikingly, tended to inversely correlate (r=-0.32, p=0.058) with IFN-γ changes from pre- to post- (i.e., 90-m, 3-d, and 7-d) surgery. Additionally, 1,25(OH)D (r=0.37, p<0.05) and the 1,25(OH)D-to-25(OH)D ratio (r=0.52, p<0.05) changes from pre- to post- (i.e., 90-m, 3-d, and 7-d) surgery correlated with those of IFN-γ. These are the first reported in vivo findings suggesting that the 25(OH)D decrease and conversion to 1,25(OH)D increase with increasing IFN-γ in the circulation. We conclude that IFN-γ contributes to the decrease in vitamin D and the conversion of vitamin D to its active hormonal form in the circulation during inflammatory insult in humans.
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