Testosterone

Understand

Overview

Testosterone is the primary androgenic hormone, produced mainly in the testes in men (Leydig cells) and in much smaller amounts in the ovaries and adrenal glands in women. Although associated chiefly with male characteristics, testosterone performs important physiological functions in both sexes — it affects muscle mass, bone density, libido, mood and cognitive function.

Testosterone levels naturally peak in early adulthood and gradually decline with age — in men, by roughly 1% per year after age 30, though the pace of that decline depends heavily on lifestyle (body composition, sleep, physical activity, stress).

Who does optimizing natural testosterone levels matter most for? Above all, men over 30, in whom the rate of decline is especially sensitive to lifestyle — obesity, physical inactivity, chronic stress and insufficient sleep clearly accelerate the process; studies show that simply restricting sleep to 5 hours a night for a week can lower daytime testosterone levels in healthy young men by as much as 10–15%. This is the group for whom improving sleep, regular resistance training and weight management have real, well-documented significance. On the other hand, for young, healthy people with a normal baseline level, popular over-the-counter 'testosterone-boosting' supplements mostly lack solid evidence of effectiveness — the exception being correcting an actually diagnosed vitamin D or zinc deficiency. People with symptoms suggesting a deficiency (reduced libido, chronic fatigue, loss of muscle mass, erectile dysfunction) should start with a blood test rather than self-treatment, since the same symptoms can have entirely different causes.

History of use

Testosterone was the first sex hormone to be isolated in pure form, in 1935, and that same year Adolf Butenandt and Leopold Ružička independently developed a method for its chemical synthesis — a discovery for which both received the Nobel Prize in Chemistry in 1939. Since then, research has progressed from basic endocrinology to modern studies on how lifestyle factors (sleep, training, body composition) affect the natural level of this hormone.