"We know that maltreatment is traumatic, but I think the point here is that even harmful parenting behaviors that may not be classified as maltreatment per se have this association with (mental) disorders," said Lisa Berlin, who studies parenting and child maltreatment at the University of Maryland School of Social Work in Baltimore.
The finding "adds to our existing worries about the use of physical punishment, and speaks to the value of non-physical discipline," Berlin, who wasn't involved in the new study, told Reuters Health. "There just seems to be one study after another... that says we can and should find different ways to discipline our kids."
Up to half of all children may be spanked as punishment, according to researchers led by Tracie Afifi at the University of Manitoba in Winnipeg - but they wanted to look at harsher punishments, such as shoving and hitting.
The study team used data collected by United States Census interviewers in 2004 and 2005 in surveys of close to 35,000 adults across the country.
The interviewers asked participants about how often they were physically punished as children, other problems their families had - such as parents who had drug problems or went to jail - and about their own symptoms of mental disorders, current or past.
Afifi and her colleagues didn't include anyone who reported being physically, sexually or emotionally abused by family members to zone in on the effect of punishment that didn't go so far as to constitute maltreatment.
They found about six percent of interview subjects had been punished beyond spanking "sometimes," "fairly often" or "very often."
And those people with a history of harsh physical punishment were more likely to have a range of mood and personality disorders or to abuse drugs and alcohol.
For example, 20 percent of people who remembered being physically punished had been depressed, and 43 percent had abused alcohol at some point. That compared to 16 percent of people who weren't hit or slapped who had been depressed, and 30 percent who drank too much.
Those links held up after the researchers took into account family problems - including which participants' parents had been treated for mental illness themselves - and interviewees' race, income and level of education.
"People believe that as long as you don't cross that line into child maltreatment, and the physical punishment is controlled and doesn't cross the line into abuse, it won't have any negative long-term consequences for the child," Afifi told Reuters Health.
"The way we see it is along a continuum of having no violence to severe violence."
She and her colleagues write in the journal Pediatrics that physical punishment may lead to chronic stress in kids, which could then increase their chance of developing depression or anxiety, for example, later on.
Michele Knox, a psychiatrist who studies family and youth violence at the University of Toledo College of Medicine, agreed that's a likely explanation.
"Physical punishment is a chronic and sometimes repeated stressor for young people, and we know that chronic and repeated stressors have a negative impact on the brain," Knox, who wasn't part of the research team, told Reuters Health.
But the findings can't prove the punishments, themselves, caused kids to develop mood and personality disorders.
Knox pointed out the interviewees might not have known if their parents had been treated for mental illness - and many people with a mental condition never get treated anyway - so those cases wouldn't be accounted for in the data. Mental illnesses like depression and anxiety are known to be at least partially genetic.
Still, Knox said, "Spanking and other forms of corporal punishment have a huge variety of negative outcomes, and almost no positive outcomes." Those negative outcomes include aggressive behavior and delinquency in kids, she added.
She said parents can make an agreement even before their child is born to never use physical punishment, and instead rely on methods like "time out" and using positive reinforcement to reward good behavior.