UW study: Long-term breastfeeding sheds light on whether an infant becomes right- or left-handed

Jackson Holtz UW News

Bottle feeding infants is associated with left-handedness, according to a new study from the University of Washington. The study found that the prevalence of left-handedness is lower among breastfed infants as compared to bottle-fed infants. This finding was identified in about 60,000 mother-infant pairs and accounted for known risk factors for handedness.

The results provide further insight into the development of complex brain functions which ultimately determine which side of the batter box the infant likely will choose.

“We think breastfeeding optimizes the process the brain undergoes when solidifying handedness,” said Philippe Hujoel, the study’s author, a professor at the UW’s School of Dentistry and an adjunct professor of epidemiology at the School of Public Health. “That’s important because it provides an independent line of evidence that breastfeeding may need to last six to nine months.”

The study does not imply, however, that breastfeeding leads to right-handedness, Hujoel said. Handedness, whether it be right- or left-handed, is set early in fetal life and is at least partially determined by genetics. The research does sheds light on when the region of the brain that controls handedness localizes to one side of the brain, a process known as brain lateralization. Possibly, the research shows, breastfeeding optimizes this lateralization towards becoming right- or left-handed.

The findings were published online last month in the journal Laterality: Asymmetries of Body, Brain and Cognition.

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