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Vitamin D is suggested to have a role in the coupling of bone resorption and formation. Compared with women, men are believed to have more stable bone remodeling, and thus, are considered less susceptible to the seasonal variation of calcitropic hormones. We examined whether seasonal variation exists in calcitropic hormones, bone remodeling markers, and BMD in healthy men. Furthermore, we determined which vitamin D intake is required to prevent this variation. Subjects (N = 48) were healthy white men 21–49 yr of age from the Helsinki area with a mean habitual dietary intake of vitamin D of 6.6 ± 5.1 (SD) μg/d. This was a 6‐mo double‐blinded vitamin D intervention study, in which subjects were allocated to three groups of 20 μg (800 IU), 10 μg (400 IU), or placebo. Fasting blood samplings were collected six times for analyses of serum (S‐)25(OH)D, iPTH, bone‐specific alkaline phosphatase (BALP …