My updated theory on autism

If you read a couple of my older posts, you'll see that I think there is a link between autism and folic acid supplementation. I started paying attention to this issue because I have a family member who rather demonizes vaccinations. I, on the other hand, believe that the alleged vaccine-autism connection has been quite thoroughly debunked. In fact, a recent study of brains of normal and autistic people found that there were too many neurons (67% more) in the cerebral cortex of the brains of those with autism, neurons which are generated only prenatally and which typically are pruned prenatally and in early infancy through programmed cell death (see this study). Instead of still suspecting vaccines in autism, we should instead pay attention to the prenatal environment.

I'm open to being proved wrong on there being a connection between folic acid supplementation and autism, particularly in light of the 2011 finding by UC Davis that women who took prenatal vitamins were less likely to have autistic children. The researchers postulated that it was because of a protective effect of folic acid. I think they're guessing on that point. Folic acid affects methylation and seems implicated in epigenetic changes, which are connected to autism (see this recent study). Some other vitamin or combination of vitamins appears to me to be more likely as the cause of the protective effect of the prenatal vitamins. Vitamin D seems a very likely candidate, especially since "developmental vitamin D deficiency increase[s] cellular proliferation in the brain and reduce[s] the amount of apoptotic cell death that is normally associated with neuronal differentiation", per this paper.

I imagine this as a possible scenario--folic acid, given with the laudable goal of preventing neural tube defects, also contributes to autism by increasing the number of neurons in the cerebral cortex, then vitamin D deficiency prevents the brain from adequately pruning the neurons to the proper number, resulting in an excess of these neurons, which prevents the brain from functioning in a neurotypical way. Please, any ideas on this? In the meantime, I'm 27 weeks pregnant, and it's nearly winter; I'm going out to buy vitamin D supplements this week.