WASHINGTON—Scientists said Monday they have new evidence about why women live longer than men, from a study of historical data showing castrated Koreans far outlived their non-eunuch contemporaries.

The study, published in the scientific journal “Current Biology,” used detailed genealogical records of the Imperial nobility during Korea’s Joseon dynasty, which spanned more than 500 years from the late 1300s to the early 1900s.

According to the data, most men, including kings and royal family members, died in their late-40s or early-50s.

But noble-class eunuchs — men who were castrated either by accident or because of social benefits — lived, on average, to the ripe, old age of 70.

Study author Kyung-Jin Min of South Korea’s Inha University, told AFP the reason is probably that manly hormone, testosterone:

“Testosterone is known to increase the incidence of coronary heart disease and reduce immune function in males,” he said.

Castration “removes the source of male sex hormones,” the study notes, adding the practice has already been proven to help many male animals live longer.

Castration also cuts off the possibility of reproduction, which Kyung-Jin noted could also be a factor.

According to “one of the leading theories of aging, aging occurs at the expense of reproduction,” he said, because the body has limited energy that can be used either to keep up reproductive function, or else to keep up everything else.

But although the eunuchs could not father children biologically, they married, adopted and raised children, and generally lived lives very similar to their non-castrated peers.

“In order to eliminate socioeconomic factors that could have affected lifespan, the lifespan of the eunuchs was compared to the lifespan of men from other Yan-ban (noble class) families with a similar socioeconomic status,” Kyung-Jin said.

And “to exclude genetic factors that could have affected the lifespan, we compared the lifespan of eunuchs with multiple Yan-ban families.”

Modern men looking to extend their lifespan could consider “testosterone reduction therapy,” but Kyung-Jin said it’s probably premature.

For one thing, it is not clear if it would have an effect if the therapy were started at an older age — the eunuchs were all castrated as children.

And for another, the therapy could have side effects that some men may feel make that longer life less worth living.

“We may need to consider the side effects of it,” Kyung-Jin said, “mainly, reduction of sex drive in males.”