Could the way you feed your bub be associated with whether they end up being right or left-handed? It certainly seems like an odd link, but that's the conclusion of a new large study of breastfeeding and handedness, recently published in the journal Laterality: Asymmetries of Body, Brain and Cognition.
The University of Washington research, which analysed data from over 60,000 mother-child pairs, found that there were fewer lefties among breastfed infants compared to those who were bottle fed.
Specifically, results indicated that compared to bottle feeding, breastfeeding for less than one month was associated with 9 per cent decreased prevalence of nonrighthandedness, while nursing for one to six months and six or more was associated with 15 per cent and 22 per cent decreased prevalence respectively.
But the association ended there. "Breastfeeding for longer than 9 months was not associated with further reductions in the prevalence for nonrighthandedness," the study notes.
So why might that be the case?
"We think breastfeeding optimises the process the brain undergoes when solidifying handedness," said lead author Professor Philippe Hujoel. "That's important because it provides an independent line of evidence that breastfeeding may need to last six to nine months."
It's important to note that the study doesn't show that breastfeeding causes right-handedness, something Professor Hujoel explains is partially down to genetics. Instead, the findings shed light on when the region of the brain that controls handedness localises to one side of the brain, a process known as brain lateralisation.
That said, Professor Hujoel notes that the effect of breastfeeding on handedness may also be unrelated to nutrition and more to do with hormonal responses associated with mother-infant bonding during breastfeeding.
The jury is still out.
It's not the first time a study has linked breastfeeding to handedness. Research published in the journal Laterality in 2012 also found that children who were breastfed for a minimum period (between one month and six weeks) were significantly less likely to be left-handed. But the researchers were also none the wiser as to why that might be the case. "Breastfeeding is an environmental factor that predicts handedness in a non-linear way, although the mechanism is unknown," they wrote at the time.
About 10 per cent of people are left-handed, with lefties more common in males (11 per cent) than females (13 per cent). Other studies have shown that being left-handed is more common in twins (8.1 per cent) and triplets (7.1 per cent) than singletons (5.8 per cent), while being ambidextrous is more common in triplets (6.4 per cent) than in twins (3.4 per cent) and singletons (3.5 per cent).
The reality is, however, does it really matter whether your bub is left or right-handed? The short answer is no. And nor is it possible for every mum to breastfeed their baby - for one reason or another - and there is absolutely no judgment from us.
While there's much we still don't know about being left or right-handed, previous studies have found no significant differences in personality traits between lefties and righties.
And when it comes to sports like baseball, cricket and table tennis, lefties certainly have the - ahem - upper hand.