A population-level decline in serum testosterone levels in American men.

Plain-language summary

This study set out to measure whether testosterone in American men had fallen over calendar time, separately from the fall that comes with getting older. It drew 2769 measurements from 1532 randomly selected men aged 45 to 79 in the Boston area, across three waves between 1987 and 2004, and compared men of the same age from different waves. Median total testosterone, meaning the middle value once the men are lined up from lowest to highest, was 501 ng/dL in the first wave, 435 ng/dL at the first follow-up and 391 ng/dL in the last wave. That is a fall of about 22 percent from first wave to last. Comparing men of the same age across waves, testosterone fell about 1.2 percent for every calendar year that passed, roughly three times the 0.4 percent a year that comes with getting older. The fall was not explained by the men getting heavier or sicker.

Key findings

• Median total testosterone fell from 501 ng/dL in the first wave to 435 ng/dL at the first follow-up and 391 ng/dL in the last, a fall of about 22 percent.
• Comparing men of the same age across waves, testosterone fell about 1.2 percent per calendar year, about three times the 0.4 percent a year that comes with age.
• The fall was not explained by changes in relative weight or health.
• The absolute medians and the yearly rates come from the full text of the paper, not from its abstract.