The Decline is Real

Men today have considerably less testosterone than men of the same age even a single generation ago. I’m not talking figuratively, like your boomer uncle might. I mean it: men today really do have considerably less testosterone than men of the same age even a single generation ago.

As part of the Massachusetts Male Aging Study, data were gathered on 1500 randomly selected men in the Boston area, in three separate periods spanning 17 years (1987-1989, 1995-97 and 2002-2004). Various biomarkers were measured, including levels of total testosterone as well as bioavailable testosterone – testosterone that can actually be used by the body. A 2007 study of the testosterone data showed that both total and bioavailable levels of testosterone decreased by 12% and 13% respectively each year, amounting to a 20.4% and a 22.1% decrease across the total span of the study.

These results are not a one-off; similar population-level declines have been observed across the Western world. To some scientists, such as those behind a 2012 study of Finnish men in the European Journal of Endocrinology, this has come as a real surprise. The researchers in the Finnish case noted that Finnish men scored comparatively well in studies of reproductive health, such as semen quality, instances of cryptorchidism (undescended testicles), and testicular cancer, and so thought they were unlikely to have suffered the significant decline seen in the Massachusetts Male Aging Study. What the researchers found, though, was a generational decline in testosterone levels that was just as significant, if not worse.

Master Hormone

Testosterone is the master male hormone and governs the masculinization process that occurs first in the womb and then during adolescence. Male processes governed by testosterone include the development of the penis and testes; deepening of the voice; the growth of facial and pubic hair; muscular and bone development; and libido and sperm production. Mood is also heavily dependent on testosterone levels. It’s likely that there are other functions governed by testosterone that we don’t yet know about.

The production of testosterone in men is regulated via the brain’s pituitary gland, which sends signals to the testes to produce testosterone. Levels of the hormone are closely regulated by a feedback loop. If testosterone levels are too high, the brain sends signals to the pituitary gland to reduce production.

Though men typically have much more testosterone than women, and women typically have much more estrogen than men, men and women need both testosterone and estrogen for their bodies to function properly. In men, estrogen has important roles to play in erectile function and libido, bone health, brain function, and lipid and skin metabolism; having low estrogen can be a very serious problem for men, just as it can be for women.