A poor diet in early life is a strong risk factor for aggression and hyperactivity in childhood and adolescence, a new study reports.
Jianghong Liu and colleagues compared 353 children who were malnourished at age 3 to a control group of about 1,200 children who did not show signs of malnutrition at this age. All of the children were participants in a long-term study conducted on the island of Mauritius, off the coast of Africa.
Children were categorized as malnourished if they exhibited any of these signs:
Liu and colleagues analyzed behavioral data taken when the children reached the ages of 8, 11, and 17, and report that "the children with malnutrition signs at age 3 years were more aggressive or hyperactive at age 8 years, had more externalizing problems at age 11, and had greater conduct disorder and excessive motor activity at age 17." These findings remained true when the researchers controlled for psychosocial factors including parental education and employment status, mother's age and marital status, quality of housing, access to toys and books, number of siblings, and presence or absence of parental mental illness.
A "dose-response" relationship was seen in the tests performed at ages 8 and 17, with a higher number of malnutrition signs correlating with a greater degree of externalizing behavior. The researchers also found that at 8 and 11, low IQ mediated the link between malnutrition and behavior problems. This indicates, Liu et al. say, that "malnutrition predisposes children to a lower IQ, which in turn predisposes them to externalizing behavior problems." They note, however, that malnutrition was associated with externalizing behavior problems at age 17 even when they controlled for IQ.
Liu and colleagues note that the malnutrition-behavior link remained strong at different ages, was detected by three different behavioral tests, and was true for both genders and for different ethnic groups included in the study. They note, however, that further research is needed to investigate whether the effects on behavior stemmed from transient or chronic malnutrition, and whether prenatal malnutrition played a role.
"We hypothesize that early malnutrition negatively affects brain growth and development," they conclude, "and that brain impairments predispose to antisocial and violent behavior by affecting cognitive functions." They cite scientific literature showing that zinc, protein, and iron deficiencies can impair brain development and predispose to aggression, as well as recent research showing that dietary improvements can lead to reductions in antisocial behavior in adult criminal offenders (see related article, Crime Times, 2002, Vol. 8, No. 3, Page 1).
"Because nutrition is a malleable factor," they say, "it may be more practical and easier to prevent externalizing behavior through better early nutrition targeting at-risk populations than more complex and expensive psychosocial manipulations." Such measures, they say, may also need to target prenatal diet in order to be effective.
"Malnutrition at age 3 years and externalizing behavior problems at ages 8, 11, and 17 years," Jianghong Liu, Adrian Raine, Peter H. Venables, and Sarnoff A. Mednick, American Journal of Psychiatry, Vol. 161, November 2004, 2005-13. Address: Adrian Raine, Department of Psychology, University of Southern California, Los Angeles, CA 90089-1061, firstname.lastname@example.org.