Figure 44. Geometric mean (95% CI) monthly variation in serum 25-hydroxyvitamin D [25(OH)D] concentrations in men (■; n = 3725) and women (□; n = 3712) in the 1958 British birth cohort at age 45 y. The interaction between sex and month was significant [p = 0.02, linear regression analyses on log 25(OH)D]. n per sex and month ranged from 17 to 340: 98 in December 2003 for women and < 100 for both sexes in December 2002 (n = 40 M, 37 F), January 2004 (n = 95 M, 75 F), February 2004 (n = 58 M, 70 F), and March 2004 (n = 22 M, 17 F). Reproduced with permission from.⁶¹