McLean, VA (written by Sharon Jayson/USA Today) -- Keith Liadis, 29, is an outdoorsy, adventurous guy who spent part of Memorial Day weekend cliff jumping with friends. "I'm kind of a risk-taker," he says.
But this mechanical engineer from Bedford, N.H., is also a married father of 1-year-old Ella, and he says being a dad has tempered his outlook.
He did a few jumps on the trip, he says, but "the very first thing that popped into my mind was 'I can't do that' " on "some of the higher-risk ones, where you have to clear some trees."
Liadis isn't alone in his altered frame of mind. While many studies in the past decade have shown that a father's involvement can improve a child's well-being, newer research finds that becoming a father affects the men, too. New fathers exhibit hormonal changes and, in turn, alter their behavior, which suggests that having children influences men in far-reaching ways.
"We're finding that (fatherhood) does have mental health, well-being and actual physical health benefits," says David DeGarmo, a research scientist at the non-profit Oregon Social Learning Center in Eugene.
DeGarmo is lead author of an 18-month study of 230 divorced fathers of kids ages 4-11 that was published in 2010 in the American Journal of Men's Health. It found that when a father was more involved with his kids, "he had better health, drank less and had lower substance use."
Other recent findings have shown that "fatherhood prompts men to be less self-centered, more giving and more outward-focused.
It can prompt them to be more responsible and become more mature, especially to temper some of their risks," says Richard Settersten Jr., professor of human development and family sciences at Oregon State University in Corvallis. He says involved fathering promotes "more positive attachments and relationships."
Psychologist David Shwalb of Southern Utah University in Cedar City says it's "somewhat surprising" that so little research has focused on how men change when they become fathers.
"I think that's because psychology and child development as fields have been so caught up in proving the importance of parents for children that they skipped the issue of influences on parents," he says.
Testosterone levels fall
Anthropologist Peter Gray of the University of Nevada-Las Vegas includes a chapter called "Babies on His Brain" in the new book he co-authored, Fatherhood: Evolution and Human Paternal Behavior.
"There's more interest in what dads are doing and, in turn, looking at documentable effects on men's psychology and behavior," he says. "This effort is also benefited by new technologies - the ability to measure testosterone in saliva opens up new research avenues. You can recruit more men to participate in studies on the physiology of fatherhood if you have measures that are less invasive than, say, blood draws."
A study published last fall in Proceedings of the National Academy of Sciences found a drop in levels of testosterone, a hormone associated with masculinity, when men became first-time fathers. It followed 624 men ages 21-26 in the Philippines for almost five years - from their pre-child days to post-fatherhood - and is considered the first large-scale longitudinal proof of a cause-and-effect relationship between fatherhood and testosterone changes.
Co-author Lee Gettler of Northwestern University in Evanston, Ill., also looked at the hormone prolactin in 289 participants; his study last month in the American Journal of Physical Anthropology found fathers have higher levels than others. "There appears to be a dramatic effect of fatherhood on these two hormones early on after men have children," he says.
A smaller study at the University of Zurich in Switzerland, published earlier this year in the journal Hormones and Behavior, found that after men had children, they had lower testosterone levels and low scores for sensation-seeking.
Michael Simmons, 30, of Plainsboro, N.J., says he's "definitely more risk-averse" since the births of daughter Halle, 3, and son Jayden, 18 months.
"It all stems from a voice in the back of my head," Simmons says. "I'll be driving somewhere and feeling like I have more responsibility. ... I wasn't a very risky person at all, but now I have that voice in my head."
Liadis says his friends from work are planning a skydiving trip later this summer, something he's wanted to try.
But "I'm really hesitant now," he says. "It's tough, because I don't want to completely stop doing these types of activities, but having a daughter who fully depends on me makes me think twice about taking those risks."