Vol. 8, No. 3, 2002 Page 5

Breast-feeding: longer duration linked to higher adult IQ

Babies breast-fed for most of their first year of life are significantly more intelligent when they grow up than are babies who receive little or no breast-feeding, according to a recent study in the Journal of the American Medical Association.

Erik Lykke Mortensen and colleagues conducted a prospective study of more than 3,000 men and women born in Copenhagen, Denmark. Participants were given IQ tests in late adolescence or early adulthood. The researchers divided the subjects into five groups based on the length of time they were breast-fed as infants, controlling for a wide range of other social and biological factors.

Of the participants, one group took the Wechsler Adult Intelligence Scale tests in early adulthood, while another group took a different IQ test ( the Børge Priens Prøve, or BPP) when they entered the military. "Duration of breast–feeding was associated with significantly higher scores on the Verbal, Performance, and Full Scale Weschsler Adult Intelligence Scale [WAIS]," the researchers say, with BPP scores showing a similar although smaller effect. The average full scale WAIS IQ score for infants nursed less than one month was 99.4; this increased to 101.7 for those nursed for 2 to 3 months, to 102.3 for those nursed 4 to 6 months, and to 106.0 for those nursed 7 to 9 months. After nine months, breast-feeding ceased to correlate with increased IQ scores.

June Machover Reinisch, a member of the research team, said, "We are really quite certain that what we are seeing here is the effect of the duration of breast-feeding on an individual's intelligence.....The evidence is growing that breast-feeding is among the most important lifelong benefits a mother can give to her child."

IQ scores are strongly linked to academic performance and job success, and reduced IQ is a powerful risk factor for delinquency and criminality.


"The association between duration of breastfeeding and adult intelligence," Erik Lykke Mortensen, Kim Fleischer Michaelsen, Stephanie A. Sanders, and June Machover Reinisch, Journal of the American Medical Association, Vol. 287, No. 18, May 8, 2002, 2365-71. Address: Erik Lykke Mortensen, Institute of Preventive Medicine, Kommunehospitalet, DK-1399 Copenhagen K, Denmark, e.l.mortensen@pubhealth.ku.dk.

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"Breast-feeding linked to IQ gain," Marc Kaufman, Washington Post, May 8, 2002, p. A01.

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