Bottle feeding in infants associated with left-handedness, finds study

Researchers at the University of Washington have found that Bottle feeding in infants is associated with left-handedness. The study found that the prevalence of left-handedness is lower among breastfed infants as compared to bottle-fed infants. The findings were published in the journal Laterality: Asymmetries of Body, Brain and Cognition.

The finding was identified in about 60,000 mother-infant pairs and accounted for known risk factors for handedness. It provides 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 shed 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 of this study offer an independent line of evidence that breastfeeding may enhance brain lateralization. This finding provides additional evidence to counter the arguments of those who dismiss breastfeeding despite its evolutionary normality, and despite the precautionary principle. Possibly, the effect of breastfeeding on handedness is unrelated to nutrition, and instead mediated by the hormonal responses associated with mother-infant bonding during breastfeeding. An alternate interpretation, of course, is that another powerfully hidden confounder, associated with breastfeeding, was missed. The safest conclusion may, therefore, be that handedness is related to nurturing.

More reliable evidence on how breastfeeding affects lateralization requires the conduct of large randomized trials.