Where Has All the Testosterone Gone?

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The Trump administration seems to harbor a hulking obsession with testosterone.

Health Secretary Robert F.

Kennedy Jr. once claimed that the president’s testosterone levels are unusually high for a man of his age, and Kennedy is known to take a supplementary dose of the male sex hormone himself.

In April, the FDA moved to expand access to testosterone-replacement therapy for greater numbers of men.

And last month, Defense Secretary Pete Hegseth announced that “warfighters” older than 30 will have their testosterone levels checked annually so that they can stay on the “leading edge of lethality.” The need for expansive testing or for testosterone replacement is questionable, according to several medical experts I spoke with.

But underneath the administration’s preoccupation lies a real trend: Although most men’s levels are still within the normal range , average testosterone has been declining among men for the past several decades.

A recent review of studies involving more than a million men all over the world found that average testosterone levels in blood have dropped by about 20 percent over the past half century.

A new, unpublished study put the decrease during that basic time period at closer to 50 p ercen t.

Some scientists are skeptical of these numbers because testosterone has been measured in different ways over time.

But Michael Eisenberg, a urologist at Stanford Medicine who specializes in male fertility, told me that the findings of a decline are “pretty solid.” The testosterone slump, he said, has “manifested across many different study designs.” Medical researchers aren’t certain what’s causing the drop.

The global population is aging, and men’s testosterone levels go down naturally as they get older—but this can’t account for the change, because most studies control for age.

One theory is that the environment is playing a role: John Meeker, an environmental-health professor at the University of Michigan, pointed to endocrine-disrupting “forever chemicals,” such as the phthalates in our plastic kitchen utensils and the PFAS in our nonstick pans.