Bottle feeding a baby is connected with being left-handed

Are you a left-handed person — creative and unique, but also at the mercy of a right-handed world?

It’s possible that whether you were breastfed played a role in your handedness.

New research by Dr. Philip Hujoel, a professor of dentistry and epidemiology at the University of Washington, suggests the two are linked, although the reason why hasn’t been determined.

Hujoel’s study found that bottle-feeding a baby is associated with being left-handed, but that doesn't necessarily mean that bottle-feeding caused it.

“It’s possible it's causal," Hujoel said. “It may be related to the breast milk itself or even to food or hormonal interactions that happen during breastfeeding.”

One example: he said there’s a higher prevalence of left-handedness in twins because they’re less likely to be breastfed.

But Hujoel said there are many reasons why some of us are left-handed — many which start before birth or at birth, like genetics and prenatal stresses.

“From about the third month in utero you can see that a fetus is starting to prefer their left or right hand," Hujoel said. "We don't know how the environmental factor of breastfeeding interacts with genetics."

There’s a long held belief that people who are left handed are at a disadvantage. “Left-handedness has been associated with lower verbal ability and a greater risk of autoimmune diseases, like Type 1 diabetes,” Hujoel said.

However, Hujoel noted, there’s no real preference to being right-handed or left-handed, so his study need not be the reason to choose breastfeeding over bottle-feeding.

"It's an epidemiological study and should not be used to tell people that all women should breastfeed because they're more likely to have a right-hander. That would be wrong,” Hujoel said.

Many medical organizations do recommend breastfeeding for at least six months, including the American Academy of Pediatrics. He said there’s proof that breastfeeding leads to better outcomes in general for children.

“There's a lot of literature on breastfeeding and brain development where you see that breastfed babies have larger brains. It’s also associated with a higher IQ and better verbal skills,” Hujoel said.

But the scientist cautioned we shouldn’t recommend breastfeeding over bottle-feeding solely based on epidemiological evidence.

“There have been so many disasters with epidemiologists recommending a particular type of nutrition," Hujoel said, "or saying this or that is healthy. And then the first randomized clinical trial shows they were wrong."

So don't be scared off of being left-handed, despite the biases in language, like how in French "gauche" means "left" or "awkward and clumsy" or in Latin "sinistra" (aka "sinister") has a double meaning of "left" or "evil."

Produced for the web by Katherine Banwell.