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In infancy, genes are the key influence on a child’s ability to deal with stress. But as early as 6 months of age, parenting plays an important role in changing the impact of genes that may put infants at risk for responding poorly to stress.

That’s the message from a new study by researchers at the University of North Carolina-Chapel Hill, Pennsylvania State University, the University of North Carolina-Greensboro, and North Carolina State University. It appears in the September/October 2008 issue of the journal Child Development.

The researchers looked at 142 infants who had been placed in a stressful situation—being separated from their mothers—when they were 3, 6, and 12 months old. They measured infants’ heart rates while they were exposed to the stressor, isolating a cardiac response called vagal tone. Vagal tone acts like a brake on the heart when the body is in a calm state, but during a challenging situation, this brake is withdrawn, allowing heart rate to increase so the body can actively deal with the challenge.

Spanking has been, and still is, a common method of child discipline used by American parents.

But mothers who report that they or their partner spanked their child in the past year are nearly three times more likely to state that they also used harsher forms of punishment than those who say their child was not spanked, according to a new study led by the Injury Prevention Research Center at the University of North Carolina at Chapel Hill.

Such punishments included behaviors considered physically abusive by the researchers, such as beating, burning, kicking, hitting with an object somewhere other than the buttocks, or shaking a child less than 2 years old.

“In addition, increases in the frequency of spanking are associated with increased odds of abuse, and mothers who report spanking on the buttocks with an object – such as a belt or a switch – are nine times more likely to report abuse, compared to mothers who report no spanking with an object,” said Adam J. Zolotor, M.D., the study’s lead author and an assistant professor in the department of family medicine in the UNC School of Medicine.

A growing number of older U.S. children are being diagnosed with attention deficit hyperactivity disorder, while diagnoses among younger children have held steady, government researchers said on Wednesday.

The report by the Centers for Disease Control and Prevention found ADHD diagnoses among children aged 12 to 17 increased by an average of 4 percent a year from 1997 to 2006. The researchers found no significant change in the percentage of children aged 6 to 11 diagnosed with ADHD over the same period.

The researchers used statistics from a national health survey that included data on 23,000 children aged 6 to 17 gathered in 2004, 2005 and 2006.