Purpose: We investigated whether serum testosterone levels vary monthly in middle-aged men. Materials and methods: A total of 8,367 middle-aged men who participated in a police health urological screening program at the National Police Hospital were included. The participants were aspirants. Total testosterone was measured early in the morning. Additionally, data on age, waist circumference, blood pressure, and fasting blood sugar, triglycerides, and high-density lipoprotein levels were collected as confounders. We also collect monthly temperature and daylight duration in Seoul. We compared the mean testosterone level in each month before and after adjusting for confounders. Results: Testosterone showed a monthly pattern with a nadir in May (4.4 ng/ml) and a peak in January (6.0 ng/ml). The mean testosterone level differed significantly across months (p < 0.001). After adjusting for confounders, testosterone still showed a monthly pattern with a nadir in May (4.5 ng/ml) and a peak in January (6.1 ng/ml). The trend lines for testosterone and daylight length in each month suggested a negative relationship, and the trend lines for testosterone and outdoor temperature suggested a negative relationship. Conclusions: Serum testosterone levels varied monthly and this variation appeared to be related to outdoor temperature and daylight duration. Our results warrant further investigation. |
Comments
Diurnal variation in serum testosterone levels is well known, but some research has also suggested, albeit inconsistently, seasonal variations.
In this study from Seoul, Korea, serum total testosterone was measured in 8,400 police officers between the ages of 40 and 50 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 lasted 2 years, allowing 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 average level was recorded in May (440 mg/dL) and the highest in January (600 ng/dL). Testosterone levels were inversely related to average outdoor temperature and daylight duration.
These observations could help explain some of the variations in testosterone levels we see in practice, although the mechanism of a seasonal effect is unknown. One limitation is that these data were cross-sectional; A large longitudinal study in which each participant has serial testosterone measurements throughout the year would be of interest.
