The Association Between Serum Vitamin D3 Levels and Autism Among Jordanian Boys.

Doctors drew blood from Jordanian boys with autism and boys without autism. They checked vitamin D3 levels and asked parents about tummy pain, diarrhea, and constipation. They also looked at EEG and calcium tests to see if low vitamin D hurt the brain or bones.

The study was simple: compare one group to another and see which kids had the lowest vitamin D.

Boys with autism had clearly lower vitamin D than the other boys. Inside the autism group, the kids with the lowest vitamin D were the same ones whose parents reported the most GI trouble. EEG and calcium scores stayed normal, so the vitamin gap was not yet harming brain waves or bones.

Chandler et al. (2013) and Kang et al. (2014) already showed that about half of kids with autism have chronic GI symptoms. Loai et al. now add a biochemical clue: low vitamin D rides along with those complaints.

Johnson et al. (2009) warned that GI prevalence numbers swing wildly—from 4 % to 97 %—because every study asks parents differently. The vitamin D link does not erase that mess; it just gives us one more measurable piece to track.

Vietti et al. (2026) report another vitamin story: nine autistic children with extreme food selectivity developed scurvy and limping, yet recovered fully with vitamin C. Together these papers signal that vitamin deficits can hide behind behavior and feeding issues.

You cannot fix autism with vitamins, but you can spot hidden pain. When a client shows new self-injury or food refusal, ask about GI history and request a simple vitamin D level from the pediatrician. Treating low vitamin D is cheap, safe, and may ease stomach pain that fuels problem behavior.