Playing in the sun (without sunscreen) may help autism.
This paper describes the idea that autism could be caused by lack of vitamin D. The author notes that the number of autism cases have gone up along with the advice to use sunscreen. The author believes that the link between vitamin D and autism should be tested in a large randomized controlled trial. He wonders if mothers who avoid the sun are more likely to give birth to children with autism. Vitamin D supplements may not be a good intervention since vitamin D does not absorb easily from the gut.