BERKELEY, CA (UroToday.com) - The studies reviewed in this manuscript illustrate the heterogeneity within the literature in regards to seasonal variations of testosterone. Whereas substantial evidence exists to support diurnal variations in testosterone, current studies on seasonal variation are limited by sample size, environments with wide-ranging temperature and day-night patterns, inconsistent protocols for the timing of laboratory assessments, and lack of accounting for potential lifestyle modifiers -- including age. Early studies on seasonal influences showed peaks in testosterone in the summer and early autumn with nadirs in the winter and early spring. A myriad of ethnically, socially, and geographically diverse studies have shown some seasonal variability in testosterone, however, these reports were often seasonally discordant. Furthermore a number of other cross-sectional and longitudinal studies have not found similar seasonal patterns. Despite improvements in study design and larger sample sizes, authors have failed to show statistically significant seasonal differences in total and free testosterone. In addition, studies with geographically similar populations have not shown parallel changes in variation, calling into question the clinical significance of their findings.[3, 4]
This review similarly highlights the impacts of melatonin, vitamin D, sleep-wake cycles, light exposure, physical activity, BMI, and waist circumference and their potential influence on seasonal alterations in androgens. Seasonal changes in the duration of the light-dark cycle are known to cause variations in activity of human endocrine systems. Light exposure and its impact on reproductive hormone variability has been assessed in a series of men living north and south of the Arctic Circle. This included measurements of 6-sulfatoxymelatonin, a by-product of melatonin, which has known associations with sleep-wake cycles and circadian rhythm. While this study identified significant correlations in the changes in testosterone, luteinizing hormone, and the excretion of 6-sulfatoxymelatonin, these associations differed in the 2 populations of men above and below the Arctic Circle, likely indicating this relationship was circumstantial.
The interrelationship between reproductive hormones, vitamin D, and seasonality has similarly been examined. In the European Male Ageing Study, vitamin D levels were positively associated with total and free testosterone, however, after adjusting for potential health and lifestyle confounders, no statistically significant associations were seen. Similarly, seasonal variation was only seen for vitamin D and notably, not testosterone. Despite the lack of cyclical associations between vitamin D and testosterone, the relationship between vitamin D deficiency and hypogonadism has important implications as both have been associated with additional comorbidities.
The potential exists that seasonal changes in androgens may be due to other factors that vary during the year, including physical activity and exercise. Seasonal changes in serum hormone levels could be attributed to alterations in habitus and subsequent changes in aromatization, however, studies examining BMI, waist-to-hip ratio and waist circumference have found inconsistent associations with testosterone. This has only lended further uncertainty in regards to the evidence for seasonal patterns of testosterone.
If significant seasonal variation of testosterone exists, then screening and laboratory assessment of potentially hypogonadal men and resultant treatment decisions would require modification from current practice. At this time, however, reproducible data for circannual variation is sparse and its inconsistencies preclude adoption of seasonal variation into current clinical guidelines. In contrast to the substantial evidence for diurnal variation, seasonal patterns of testosterone cannot yet be deemed clinically significant based on the current literature and require further study for clarification.
- Smals AG, Kloppenborg PW, Benraad TJ. Circannual cycle in plasma testosterone levels in man. J Clin Endocrinol Metab. 1976;42: 979-82.
- Moskovic DJ, Eisenberg ML, Lipshultz LI. Seasonal Fluctionations in Testosterone:Estrogen Ratio in Men from the Southwest United States. J Androl. 2012.
- Svartberg J, Jorde R, Sundsfjord J, Bonaa KH, Barrett-Connor E. Seasonal variation of testosterone and waist to hip ratio in men: the Tromso study. J Clin Endocrinol Metab. 2003;88: 3099-104.
- Andersson AM, Carlsen E, Petersen JH, Skakkebaek NE. Variation in levels of serum inhibin B, testosterone, estradiol, luteinizing hormone, follicle-stimulating hormone, and sex hormone-binding globulin in monthly samples from healthy men during a 17-month period: possible effects of seasons. J Clin Endocrinol Metab. 2003;88: 932-7.
- Ruhayel Y, Malm G, Haugen TB, et al. Seasonal variation in serum concentrations of reproductive hormones and urinary excretion of 6-sulfatoxymelatonin in men living north and south of the Arctic Circle: a longitudinal study. Clin Endocrinol (Oxf). 2007;67: 85-92.
- Lee DM, Tajar A, Pye SR, et al. Association of hypogonadism with vitamin D status: the European Male Ageing Study. European Journal of Endocrinology / European Federation of Endocrine Societies. 2012;166: 77-85.
Ryan P. Smith, MD and Larry I. Lipshultz, MD as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
Scott Department of Urology, Baylor College of Medicine, Houston, TX USA