Eunuch study may explain why women live longer than men

Women live at least 5 years longer than men, on average in the industrialized world, previous studies have shown.

Now, a study of eunuchs from 16th to 19th century Korea suggest that testosterone may be what’s shortening men’s lives. ScienceNOW reports.

The idea that testosterone affects lifespan isn't new. After all, neutered dogs often live longer than their intact counterparts. But studies on the connection between castration and longevity in humans are harder to come by, and the results -- from a study on institutionalized patients in Kansas and Italian castrati musicians -- have been inconclusive.

So Kyung-Jin Min of Inha University and colleagues turned to Korea’s historical records.

Until the late 19th century, Korean rulers employed eunuchs to serve the royal court. These eunuchs were allowed to marry and adopt castrated boys as their sons. The Yang-Se-Gye-Bo, a genealogical record of the eunuch families, has survived, and it documents the birth and death dates and other personal details of 385 eunuchs who lived between the mid-16th century and the mid-19th century.

From this, the team verified the lifespans for 81 eunuchs. To rule out the effects of cushy conditions on longevity, they compared the eunuchs' lifespans to those of uncastrated men of similar social status living at the same time:

• The average lifespan was 70 years.
• Eunuchs outlived their uncastrated contemporaries by 14 to 19 years.
• The 81 eunuch group also boasted 3 centenarians. Current incidence of centenarians is just 1 in 3500 in Japan and 1 in 4400 in the U.S.

This is the strongest evidence yet that testosterone -- the key difference between the eunuchs and their peers in this study and a proxy for the difference between women and men -- plays a role.

So can castration really prolong a man’s life? New Scientist asks.

The conclusion supports the theory that testosterone-fueled reproduction comes at a price: increasing the risk of heart disease and cancer, and reducing the strength of the immune system.

"It's possible that testosterone reduction therapy extends male lifespan," Min says. “But Korean eunuchs were usually castrated before adolescence, so we don't know the effects of castration on lifespan in older men.”

When testosterone is lacking, the demand for amino acids to support muscle-building is decreased. Perhaps the body then shifts the use of these basic building blocks towards cellular defense and stress resistance.

The study was published in Current Biology this week.

[Via ScienceNOW, New Scientist]

Image: Geunjeongjeon from the Chosun Dynasty / Wikimedia

This post was originally published on Smartplanet.com