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Diurnal variation in serum testosterone levels is well known, but some research also has suggested — albeit inconsistently — seasonal variation. In this study from Seoul, Korea, serum total testosterone was measured in 8400 police officers in their 40s and 50s as part of a “urological health screening program.” Each participant was tested only once (in the morning, around 8:00 AM) during the study, but the program spanned 2 years, which allowed the researchers to examine correlations between testosterone levels and months.
The researchers found a substantial seasonal correlation: Mean total testosterone was lowest in spring and summer and significantly higher in fall and winter. The lowest mean level was in May (440 mg/dL), and the highest w…