Circulating total 25(OH)D and calculated free 25(OH)D in professional academy footballers at a northerly latitude in the UK.

There is limited data on the vitamin D status of UK-based professional academy footballers. Therefore, the objective of this study was to report total 25(OH)D, free 25(OH)D and free 1, 25(OH)D at the end of the winter (March) and summer periods (October) in a cohort (n = 27) of professional academy footballers in northern England. Blood samples were collected to measure total 25(OH)D, parathyroid hormone, vitamin D binding protein, albumin and calcium. Free 25(OH)D and 1, 25(OH)D were calculated. Dietary vitamin D intake and retrospective summer sunlight exposure were also collected. At the end of winter, 2/27 (7.4%) players were vitamin D deficient (25(OH)D < 30 nmol/l) and 11/27 (40.7%) were insufficient (25(OH)D > 30 nmol/l < 50 nmol/l). By the end of summer, none were deficient but 3/14 (21.4%) were still insufficient. Median total 25(OH)D (82.2 nmol/l [IQR: 50.3-90.2] vs. 54.2 nmol/l [IQR: 36.8-71.9]; P = .02), free 25(OH)D (25.8 pmol/l [IQR: 15.1-33.1] vs. 13.2 pmol/l [IQR: 9.0-14.9]; P = .005) and free 1, 25(OH)D (389 fmol/l [IQR: 209-594] vs. 212 fmol/l [IQR: 108-278]; P = .034) were significantly higher at the end of summer than the end of winter. At the end of winter, free 25(OH)D was lower (P = .003) in those vitamin D insufficient (8.8 pmol/l [IQR: 5.5-11.8]) vs. sufficient (13.7 pmol/l [IQR: 12.0-17.0]). There was a high prevalence of vitamin D insufficiency at the end of the winter. Free 25(OH)D was also lower at the winter timepoint and in players that were insufficient vs. sufficient.