NEW YORK (Reuters Life!) - Men who face plenty of competition to find a mate have slightly shorter lives than those who don't.
New research shows that gender imbalance, when men outnumber women, affects male longevity by an average of about three months.
Although the link between gender ratio and longevity has been shown in animals, the study published in the journal Demography is thought to be the first to show the impact in humans.
"If you're having a hard time finding a mate, it winds up affecting your body and how long you live," said Professor Nicholas Christakis, of Harvard Medical School.
Three months may not seem like much, he added, but it is comparable to the effects of taking a daily aspirin, or engaging in moderate exercise.
"A 65-year-old man is typically expected to live another 15.4 years. Removing three months from this block of time is significant," he explained.
Christakis and scientists from Northwestern University, the University of Wisconsin-Madison and the Chinese University of Hong Kong found that the more imbalanced the ratio of men to women, the more pronounced the effect was.
The researchers studied data from the Wisconsin Longitudinal Study, which tracked the long-term health of 4,183 men who graduated from Wisconsin high schools in 1957, and information about more than 7 million men enrolled in Medicare, the government medical program for the elderly.
After calculating the gender ratios for each high school class they noticed that 50 years later men from classes with more boys than girls did not live as long as those from more balanced classes.
Although they do not know what could explain the discrepancy, the researchers suspect it is due to social and biological factors, including the stress of finding a partner in a competitive environment.
"You might get married, but you might have to delay marriage. You might wind up getting married much later and since we know from other evidence that marriage is good for your health, you may have had less opportunity to get that benefit because you were forced to marry later," Christakis added.
Reporting by Daniel Lippman; Editing by Patricia Reaney