When Real Men Become Fathers

Fatherhood brings many changes, but one of them may be particularly surprising: a drop in testosterone levels. Researchers suspect it's because a man with children no longer needs to compete with other men for a mate.

Although the study findings don't prove that fatherhood directly affects testosterone levels, nor how a man's hormonal systems detect fatherhood, researchers did find that once men become fathers, they experience "a really dramatic" reduction in testosterone levels, says study author Lee T. Gettler, Ph.D., at Northwestern University.

"There's something that's going on in their first months that's helping them transition to their role as fathers," Dr. Gettler says.

Kids vs. no kids

The researchers examined results of blood tests of 624 young men in the Philippines who were followed over 4.5 years. Those who got married or found long-term girlfriends and became fathers were more likely to have higher testosterone levels before fatherhood.

Once they became fathers, however, their testosterone levels dropped by 26 to 34 percent, depending on the time of day it was measured. That's roughly twice as much of a drop in testosterone levels as the single men who didn't become fathers. And, the drop in testosterone levels was even more dramatic in those men who were directly involved in caring for their child.

Focus on children

Dr. Gettler doesn't think the lower testosterone level makes men less tough or less masculine. But, it might make them more attuned to the needs of their kids and less oriented toward competing with other men for the attention of women or engaging in risky behavior.

"Our assumption is that there's something about physically interacting with their kids, whether it's through sight or smell or physical touch, that activates something in the brain of men and has this trickle-down effect," Dr. Gettler says.

Stronger family ties

One theory is that lower testosterone levels might be a side effect of the increase in bonding hormones such as oxytocin and prolactin.

Robert J. Quinlan, Ph.D., at Washington State University, sees these findings as a possible opportunity for strengthening family ties.

"One might manipulate the system by encouraging fathers to get the early experience with children that lowers testosterone levels, and then perhaps family stability and child outcomes would improve," he says.

Always talk with your health care provider to find out more information.