(CBS/AP) Call it heartening news for dear old dad. New research shows that fathers are less likely than childless men to die of heart-related problems.
The study is the largest ever on male fertility and mortality, involving nearly 138,000 men. Though it didn't prove that fatherhood and cardiac mortality are linked, there is reason to believe they might be, several heart disease experts said.
Marriage, having lots of friends and even owning a dog can curb the risk for heart trouble and death, previous studies suggested. Similarly, kids might help take care of good old dad, or give him a reason to take better care of himself.
Also, it takes reasonably good genes to father a child. An inability to do so might mean a genetic weakness that spells heart trouble down the road.
"There is emerging evidence that male infertility is a window into a man's later health," said Dr. Michael Eisenberg, a Stanford University urologist who led the study. "Maybe it's telling us that something else is involved in their inability to have kids."
The study - by the AARP, the government, and several universities - was published online Monday by the journal Human Reproduction.
Last week, a study by other researchers of 600 Filipino men showed that testosterone levels fall after a man becomes a dad. Men who started out with high levels of the male hormone were more likely to become fathers, suggesting that low levels might reflect an underlying health issue that prevents reproduction, Eisenberg said.
In general, high levels of testosterone are better, but too much or too little can cause a decline in "good" HDL cholesterol a key heart disease risk factor, said Dr. Robert Eckel, past-president of the American Heart Association and professor of medicine at the University of Colorado, Denver.
"This is a hot topic," Eckel said. "I like this study because I have five children," he joked, but he said many factors such as job stress affect heart risks and the decision to have kids.
Researchers admit they couldn't measure factors like stress, but they said they did their best to account for the ones they could. They started with more than 500,000 AARP members age 50 and over who filled out periodic surveys starting in the 1990s for a research project sponsored by the National Cancer Institute.
The researchers excluded men who had never been married so they could focus on those most likely to have the intent and opportunity to father a child. Men with cancer or heart disease also were excluded to compare just men who were healthy when the study began.
Of the remaining 137,903 guys, 92 percent were fathers and half had three or more children. After an average of 10 years of follow-up, about 10 percent had died. Researchers calculated death rates according to the number of children, and adjusted for differences in smoking, weight, age, household income and other factors.
There were no difference in death rates between childless men and fathers. But dads were 17 percent less likely to have died of cardiovascular causes than childless men were.
Now for the caveats.
Researchers don't know how many men were childless by choice and not because of a fertility problem, nor do they know what fertility problems the men's partners might have had.
They didn't have information about the men's cholesterol or blood pressure levels.
Less than 5 percent of the men were blacks or other minorities, so the results may not apply to them.
Those questions aside, however, prominent heart experts were reassured by the study's large size and the steps taken to adjust for cardiac risk factors.
"I think there's something there," and social science supports the idea that children can lower heart risks, said Dr. Eric Topol, a cardiologist at Scripps Health in La Jolla, Calif. "Whether it's with a pet, a spouse or social interaction ... all those things are associated with better outcomes."
Dr. Daniel Rader, director of preventive cardiology at the University of Pennsylvania, said: "It's biologically plausible that there's a connection," but the reduced risk attributed to having children "is pretty modest."