Lack of seasonal variation in serum sex hormone levels in middle-aged to older men in the Boston area

Context: Previous studies of seasonal variation of testosterone and other hormones in men have produced mixed results regarding the number and timing of peaks and nadirs and whether hormones vary seasonally at all. Wide variation in study designs, sample sizes, analytical methods, and characteristics of the study populations may account for the heterogeneity of results. Objective: The objective of the study was to determine whether serum total, free, and bioavailable testosterone, dihydrotestosterone, SHBG, LH, dehydroepiandrosterone, dehydroepiandrosterone sulfate, estrone, estradiol, and cortisol vary seasonally in men. Design: Two blood samples were drawn 1-3 d apart at study entry and again 3 and 6 months later ( maximum six samples per subject). Hormone levels 1-3 d apart were averaged to reduce short-term intrasubject variation. Setting: The study population consisted of a community-dwelling population ( Boston, MA). Study Participants: One hundred thirty-four men 30-79 yr old were randomly selected from the respondents to the Boston Area Community Health Survey. One hundred twenty-one men who completed all six visits were included in the analysis. Main Outcome Measures: In a repeated-measures analysis, 3-month change in hormone levels, measured twice per subject, and in a sinusoidal nonlinear regression with random subject effects, average hormone level in samples 1-3 d apart were measured. Results: Aside from cortisol, no evidence of seasonal variation in hormone levels was found. The amplitude of seasonal variation was much smaller than total intraindividual variation for all hormones considered. Conclusions: Seasonal variation is likely an unimportant source of variation clinically and in epidemiological studies of hormone levels.