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updated 9/26/2011 5:00:21 PM ET 2011-09-26T21:00:21

Dads are less likely to die of heart disease than men who’ve never had kids, a study out Monday found, raising new questions about a possible biological link between male infertility and overall health.

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Other recent studies have found a connection between testicular and prostate cancer and infertility.

In the new study, the largest ever to look at fertility and mortality, researchers analyzed a decade’s worth of data about 135,000 male AARP members.

At the beginning of the decade, none of the men had ever been diagnosed with heart disease or stroke, and all of them were either married or had been married. More than nine out of 10 of the men, whose average age was around 63 at the beginning, had fathered children.

Lead author Dr. Michael Eisenberg, an assistant professor at Stanford University, may be a urologist, but he’s concerned about his patients’ other body parts, too.

His specialty, Eisenberg says, is “sort of the first line for male infertility.” And considering that approximately a third of the male human genome is involved in reproduction, it’s not surprising that Eisenberg and other researchers suspect infertility might be a tip off to an increased risk of other health problems in men.

Eisenberg and his coauthors used the number of children men had as a stand-in for whether they were infertile. While some of these men may have remained childless by choice, the researcher says that's not usually the case. They cite a nationwide survey of childless married U.S. men of reproductive age that found three out of four wanted kids.

During the decade covered by Eisenberg’s study, about 10 percent of the men died, and about one in five of the deaths were blamed on heart disease.

In a paper posted online in Human Reproduction, the authors report that, after accounting for sociodemographic factors such as education and heart disease risk factors such as diabetes and body-mass index, childless men were 17 percent more likely to have died of heart disease during the decade than the men who were fathers.

“A lot of times when we see men for infertility, they’re very young,” Eisenberg says. “A lot of these men are totally healthy. It’s sort of eye-opening to hear there could be something else going on.”

That something else could be impaired testicular function, thought to be a risk factor for heart disease, the researchers write. Testosterone deficiency in infertile men shouldn’t be confused with the widely publicized recent finding that fertile men’s testosterone levels normally drop when they become dads, Eisenberg and his coauthors say.

The researchers didn’t have information about their subjects’ testosterone levels or whether they lived with their children.

“There may be more than just a biologic reason” for the childless men’s higher risk of dying of heart disease, Eisenberg says. After all, other studies have shown men who live alone tend to die sooner than men who don’t, he says, and maybe having kids spurs men to take better care of themselves.

Eisenberg is now analyzing cardiovascular disease in a database of men who’ve undergone semen analysis, usually one of the first tests performed to check for infertility.

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