CHICAGO -- Just like new moms, new fathers can be depressed, and a study found a surprising number of sad dads spanked their 1-year-olds.

About 40 percent of depressed fathers in a survey said they'd spanked kids that age, versus just 13 percent of fathers who weren't depressed. Most dads also had had recent contact with their child's doctor - a missed opportunity to get help, authors of the study said.

The American Academy of Pediatrics and many child development experts warn against spanking children of any age. Other studies have shown that kids who are spanked are at risk of being physically abused and becoming aggressive themselves.

The researchers said spanking is especially troubling in children who are only 1, because they could get injured and they "are unlikely to understand the connection between their behavior and subsequent punishment."

The study was released online Monday in the journal Pediatrics.

The authors analyzed data on 1,746 fathers from a nationally representative survey in 16 large U.S. cities, conducted in 1999-2000. Lead author Dr. Neal Davis said that was the most recent comprehensive data on the subject, and he believes it is relevant today. Depression among fathers is strongly tied to unemployment rates, which are much higher now than a decade ago, he said.

The men were questioned about depression symptoms, spanking and interactions with their 1-year-olds, but weren't asked why they spanked or whether it resulted in physical harm.

Overall, 7 percent of dads had experienced recent major depression.

Some likely had a history of depression, but in others it was probably tied to their children's birth, similar to postpartum depression in women, Davis said. A pediatrician now with Intermountain Healthcare in Murray, Utah, Davis did the research while at the University of Michigan.

Postpartum depression is more common in women; by some estimates as many as 25 percent develop it shortly after childbirth. Severe cases have been linked with suicide and with deaths in children including several high-profile drownings.

Less is known about depression in new dads and the study raises important awareness about an under-recognized problem, said Dr. Craig Garfield, an assistant pediatrics professor at Northwestern University and co-author of a Pediatrics editorial.

With fathers increasingly spending time on child care, including taking their kids to routine doctor visits, it's important for pediatricians to pay attention to dads' mental health, Garfield said. Close to 80 percent of depressed and non-depressed dads had recent contact with their child's doctor, according to the study.