Breastfeeding predicts handedness

There are many studies of the effects of breastfeeding on the health of babies (and their mothers). There are also numerous theories about the causes of left-handedness. Many of the latter have not found strong empirical support although it seems clear that handedness is heritable. A connection between these phenomena has not hitherto been noticed.
In a paper, with the above title & forthcoming in Laterality, I show using data for Ireland (GUI) and the UK (NCDS) that children who have been breastfed for more than a minimum of 4-6 weeks are significantly less likely to be left-handed. Abstract below:

This study examines whether being breastfed predicts handedness. Two large representative samples from Britain (n=13,421) and Ireland (n=8,426) are used. Multivariate probit models are estimated, reporting the marginal effects of covariates on the probability of a child being right-handed. For both datasets, children who have been breastfed for a minimum period (between one month and six weeks) are significantly less likely to be left-handed. The results are robust to a variety of controls. Hence breastfeeding is an environmental factor that predicts handedness in a non-linear way although the mechanism is unknown.

Graph of the year? Mother's education and breastfeeding

Its that time when people reflect on the year gone by, lists of pivotal events, dead celebs etc. There are also lots of suggestions for "graph of the year" going round. It's pretty arbitrary of course since it depends on what people find interesting. Graphs are great but they have the potential to mislead since, by their nature, they are simple but evocative.
Anyway, here is one I find very striking. It graphs the rate of breastfeeding initiation (i.e. whether the child is breastfed at all) by their mother's education level using the Growing Up in Ireland data. It is one of the most pronounced socio-economic gradients I have come across. A child whose mother is a graduate has about a 77% chance of being breastfed. At the other end of the scale it is a staggering 17%. If, instead of looking at "ever" you look at a duration of "6 weeks+" the story is much the same.
Note that the average (i.e. the % ever breastfed, using sampling weights) is about 45% which is way lower than pretty much anywhere else I have looked at. The US and UK data are in the low 70's. Many countries are higher. Why there is such a low average and such a steep socio-economic gradient in Ireland I don't know. But given the benefits to mother and child it should be a matter for concern - and action.