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You probably know your body runs on a daily clock, with energy dipping in the afternoon and sleep arriving at night. Fewer people realize some of your hormones may also follow a yearly one.
In 2022, researchers in Israel published a study in the International Journal of Endocrinology. They pulled medical records for 27,328 men between the ages of 20 and 70 from the country's largest healthcare organization.
The team tracked total testosterone across the calendar. Levels climbed through summer and hit their highest point from August to October, at roughly 15.7, 15.7 and 15.4 nmol/L.
After that, the numbers slid downhill. The lowest point arrived in March, which means the same man could carry noticeably different hormone levels depending on the month he walked into the clinic.
You might assume age, body weight or heart disease explained the pattern. The researchers checked, and the seasonal swing held up independent of age, BMI and cardiovascular risk factors.
Women show up in the research too, though the evidence is thinner. A saliva study of 718 people found both men and normally cycling women had significant seasonal swings, with men peaking in fall and bottoming out in spring.
Not every study agrees on the exact month, and the researchers note that work on women has produced conflicting results. A Norwegian study of 1,548 men even found a smaller February bump, so autumn is where testosterone tends to peak, not a perfect rule.
