Spanking children might make them more aggressive later, researchers found.

* Explain to interested patients that this observational study could not establish a causal relationship between spanking and child aggression, although the findings of a positive association are consistent with numerous previous studies.

Three-year-old children whose mothers reported spanking them more than twice a month were 50% more likely to have high levels of aggression at age 5 than those who were not spanked (OR 1.49, 95% CI 1.24 to 1.78), according to Catherine Taylor, PhD, MSW, MPH, of Tulane University School of Public Health and Tropical Medicine in New Orleans, and colleagues.

The findings are consistent with several previous studies looking at corporal punishment, they reported in the May issue of Pediatrics.

Although none could establish a causal relationship with aggression, Taylor and her colleagues wrote, "this evidence base suggests that primary prevention of violence can start with efforts to prevent the use of corporal punishment against children."

Pediatrician-delivered interventions designed to teach parents nonphysical methods of discipline have yielded mixed results.

"Research to further such efforts is needed," the researchers wrote, "given that parents cite pediatricians as the professionals from whom they are most likely to seek advice regarding child discipline."

In addition, they said, broad population-based efforts should be used to change the mindset of parents, the majority of whom believe spanking a child is acceptable. In a 2005 U.S. poll, 72% of adults said it was okay to spank a child.

That's despite guidance from the American Academy of Pediatrics, which recommends that parents be encouraged and assisted in coming up with nonphysical disciplinary methods.

To further explore the link between corporal punishment and aggression in children, Taylor and her colleagues turned to the Fragile Families and Child Well-Being Study, a population-based analysis of children born in 20 large U.S. cities.

Mothers were asked to provide information on their use of corporal punishment, their child's aggressive behavior at ages 3 and 5 years, and several other related variables.

Overall, 45.6% said they never spanked their child, 27.9% reported spanking their child once or twice in the month preceding the interview, and 26.5% reported spanking their child more than twice in the previous month.

Increasing frequency of spanking was associated with greater levels of several maternal parenting risk factors, including physical and psychological maltreatment of the child by the mother, neglect, maternal exposure to intimate partner violence, and maternal stress, depression, substance use, and consideration of abortion (P<0.05 for all).

Each of the maternal parenting risk factors was also associated with higher levels of aggression in the children (P<0.01 for all).

In a fully adjusted model accounting for the child's baseline levels of aggression, parental risk factors, and all demographic variables, children who were spanked the most at age 3 had an increased risk of high levels of aggression at age 5 (P<0.0001).

The authors acknowledged several limitations of the study, including the lack of information about the use of corporal punishment by anyone other than the mother, the use of self-reported data, which is subject to bias, and the possibility that unmeasured confounders explained the findings.