A supplement containing the active form of vitamin D was shown to prevent autistic-like behaviors in mice that are predisposed to them. The active vitamin D was given to pregnant mice during the first trimester and this prevented deficits in social interaction, basic learning, and stereotyped behaviors. While this study did not find a mechanism, I published a study in 2014 suggesting that low maternal vitamin D may increase the risk of autism because vitamin D controls the production of serotonin. Serotonin acts as a brain morphogen during early brain development and it shapes the structure and wiring of the developing brain. Low brain serotonin during development has also been linked to autism. It is unclear what maternal vitamin D levels are optimal but I like to shoot for levels between 40-60 ng/ml based on all-cause mortality studies. Levels above 30 ng/ml are considered sufficient. I like to measure vitamin D levels even after supplementation to make sure that I am getting the right amount (not too low or high). I take between 2,000 IU to 4,000 IU of vitamin D3 per day, depending on the season.