Is Left-Handedness Linked to Health Problems?

My 3.5-year-old son is a very strong lefty. Literally since he could grasp at things, it’s always been with his left hand, and he plays sports left-handed too. I’ve been reading lately about links between strong left-handedness, dyslexia, and autoimmune issues. What do you make of the quality of the research evidence? Are there other things to consider about the health and well-being of my kiddo (besides left-handed scissors)?
—Southpaw Mama

The academic literature on this question is extremely interesting. The origin is a theory in 1982, by three people (Geschwind, Behan, and Galaburda — usually called GBG in these papers). They hypothesize, based on a small amount of data, that left-handedness is associated with dyslexia in particular. Over time, other papers have linked it with other neurobehavioral conditions (like ADHD) and autoimmune issues (as you note). The proposed mechanism is testosterone-related. And men are more likely to be left-handed.

A left-handed child draws smiling figures with colored pencils. — Getty Images

The data on this is equivocal. We have, on one hand, papers like this one, which focuses on boys and shows no link between handedness and any child outcomes measured. On the other, papers like this one do show a link between handedness and immune issues at a family level. In general, this literature is quite old — this was a more active debate in the 1990s than today.

This topic is hard to study because of variation in how different researchers define handedness; lack of data; and the fact that for a long time left-handedness was basically trained out of people. Bottom line: while there is some evidence suggesting slightly different brain chemistry in left-handed people, mostly we do not know.

Should you worry? Only if that’s productive, and worrying rarely is. You would face any of these challenges in the same way regardless of whether they were foreshadowed by left-handedness.

On the plus side, six of the most recent 14 presidents were left-handed, which is way more than the population share. So maybe your son will be president. It’s the only obvious conclusion.