Testicular endocrine function in the ageing male.

The decrease of plasma testosterone (T) in elderly men may be inherent to the ageing process or secondary to environmental factors such as stress, smoking and physical activity. Plasma T, apparent free T and gonadotropin levels were determined in healthy men aged 26-90 yr living under identical conditions (as monks in a monastery). We found a highly significant age-dependent decrease in T and apparent free T levels, and an increase in gonadotropin levels. The nyctohemeral variation in T levels was lower in elderly than in younger males. When studied in a larger group, smokers had higher T levels than non-smokers, whereas in young men plasma T levels were more sensitive to stress than in elderly men. Neither moderate physical activity, diet nor residence consistently altered plasma T levels. We conclude that the age-associated decrease in plasma T levels is inherent to the ageing process and that the major cause is at the testicular level, although there is evidence for subtle alterations at the hypothalamo-pituitary level.