Monthly Variations in Testosterone Levels: Results from 8,367 Middle-Aged Men

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Nelson Vergel

Monthly Variations in Serum Testosterone Levels: Results from 8,367 Middle-Aged Men

Jun Ho Lee 1, Sung Won Lee 2

J Urol. 2020 Dec 22;101097JU0000000000001546. doi: 10.1097/JU.0000000000001546. Online ahead of print.

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 officer urological health screening program at National Police Hospital were included. The participants were applicants. Total testosterone was measured early in the morning. Additionally, data on age, waist circumference, blood pressure, and levels of fasting blood sugar, triglycerides, and high-density lipoprotein were collected as confounders. We also collected the 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 (lowest concentration) in May (4.4 ng/mL or 440 ng/dL) and a peak in January (6.0 ng/mL or 600 ng/dL). The mean testosterone level differed significantly across the 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 trendlines of testosterone and the daylight duration in each month suggested a negative relationship, and the trendlines of testosterone and outdoor temperature suggested a negative relationship.

testosterone per month and sunlight.jpg

testosterone month outdoor temperature.jpg

Conclusions: The serum testosterone levels varied monthly, and this variation seems to be related to outdoor temperature and daylight duration. Our results warrant further investigation.

Keywords: Daylight; Monthly variation; Temperature; Testosterone.

Note: This study infers that men have higher testosterone in darker & colder months. Also note that the highest testosterone level was 600 ng/dL.
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Nelson Vergel

Variation in levels of serum testosterone in monthly samples from healthy men
Eur Urol Open Sci 2020;19(Suppl 2):e130

Lee J.H.

National Police Hospital, Dept. of Urology, Seoul, South Korea

Introduction & Objectives: It is well known that testosterone deficiency syndrome is related to increased insulin resistance, increased visceral fat, and erectile dysfunction. Therefore, the testosterone level is an important issue of men`s health. Daily fluctuations in testosterone have been reported in many articles. However, there has been little evidence concerning monthly fluctuations in testosterone and their results are inconsistent
across studies.

In this study, we investigated the aforementioned issues.

Materials & Methods: We enrolled a total of 9,318 middle-aged men who had received health check-ups from 2011 to 2013. We excluded participants who had taken 5 alpha-reductase inhibitors or anti-psychotics, received androgen replacement therapy, and diagnosed with any kind of cancer. Serum testosterone was measured via radioimmunoassay and serum was collected between 7:00 and 9:00 AM. Analyses were conducted with the R statistical package.

Results: Mean age, BMI, and testosterone were 50.6±5.5 years old, 25.1±2.7kg/m2, and 5.2±1.6ng/mL, respectively. And 37.4% of participants had metabolic syndrome. The trough testosterone level was observed in May (4.46ng/mL) and the peak level was observed in Jan (5.94ng/mL). The relative difference ((peak – trough)/peak) was 24.9% and absolute difference (peak - trough) was 1.48ng/mL. The ratio of testosterone <3.5ng/mL was highest in May (23.4%) and lowest in Jan (3.0%) (P<.001). After adjusting age, BMI, and the number of metabolic syndromes, the trough testosterone level was also observed in May and the peak level in Jan. (adjusted mean (95% CI)ng/mL; May, 4.390(4.239-4.542); Jan., 5.968(5.832-6.104))

Conclusions: We found that monthly variation in levels of testosterone. In the diagnosis of testosterone deficiency, careful consideration of monthly variation in levels of testosterone would be needed. Further investigational studies would be needed to confirm our data.

Nelson Vergel

Another study with very different results. I think it depends on region, sample size, and other factors.

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
Andersson, Anna-Maria ; Carlsen, Elisabeth ; Petersen, Jørgen Holm ; Skakkebæk, Niels Erik
The Journal of Clinical Endocrinology & Metabolism, 2003-02, Vol.88 (2), p.932-937

seasonal variations of testosterone in men.jpg

To obtain information on the scale of the intraindividual variation in testicular hormone, blood samples for inhibin B determination were collected monthly in 27 healthy male volunteers during a 17-month period. In addition, the traditional reproductive hormones FSH, LH, testosterone, estradiol, and SHBG were measured. The intraindividual variation in inhibin B over the study period was, on the average, 10%, corresponding to the assay variation of the inhibin B assay, indicating that most of the observed day to day variation in inhibin B levels in men could be explained by assay variation. A seasonal variation was observed in LH and testosterone levels, but not in the levels of the other hormones. The seasonal variation in testosterone levels could be explained by the variation in LH levels. The seasonal variation in LH levels seemed to be related to the mean air temperature during the month before blood sampling, but not to the length of daylight or the hours of sunshine. In conclusion, our data showed that day to day levels of inhibin B are relatively constant in men and do not seem to be influenced by seasonal factors. In contrast, we found a seasonal variation in LH and testosterone levels in men. The peak levels of both LH and testosterone were observed during June-July, with minimum levels present during winter-early spring. Air temperature, rather than light exposure, seems to be a possible climatic variable explaining the seasonal variation in LH levels.


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Active Member
The second study coincides with my experience and my indirect observations: sexual activity seems to peak during the hot summer and substantially decreases during the cold winter.

The second study mentions that the seasonal pattern was evident on the individual plots of 12 of the 27 men, with the remaining men showing no pattern. That to me is the biggest proof than any fancy "regression models", although it remains unclear why the remaining 15 men did not show seasonal pattern.

The statistical methods in the first (Korean) study are not clear but if they had different random participants each month and plotted the mean values each month, they are averaging over large individual differences (independent measures statistical design), with is incorrect. Each individual/participant should be compared to his own levels i.e. "individual plot". This is the so called 'repeated measures statistical design'.
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