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Dear Dr. Cannell: Will vitamin D improve my son’s autistic symptoms?

Posted on: March 28, 2018   by  John Cannell, MD


Dear Dr. Cannell:

My 25-month-old son has developed symptoms of autism.  He has stopped talking, is flapping his hand about 2-3 hours/day and no longer seems to recognize faces. My husband and I are desperate.

Although we are waiting to see a neurologist, we do not want to delay treating him with anything that might help, like vitamin D. My husband and I are very interested in the link between vitamin D deficiency and autism.

My son has had very little sun exposure and I weaned him on fruit juice. We requested a vitamin D blood test.  Shockingly, his 25(OH)D level was only 7 ng/ml.

After reading your book, we want to give him high doses of vitamin D.  He weighs 14kg so that would mean I would need to give him about 4,000 IU/day?  I would like to give him 5,000 IU/day as his vitamin D level is so low.  Is this safe, and how long would I need to give him vitamin D to achieve a level of around 80ng/ml?

What can we expect if he responds to vitamin D?

Thank you for all you do.



Dear Mira:

Yes, you can safely give him 5,000 IU/day, and that is exactly what I recommend. It will take several months to get his 25(OH)D levels up to 80 ng/ml and he will probably require more than 5,000 IU/day to obtain that level. I explain this in detail in my book about autism and vitamin D.  Also, believe it or not, I’ve written 139 blogs that include the word “autism.”

The two randomized controlled trials published to date using vitamin D to treat autism used the equivalent of 300 IU/KG/day, which is 4,200 IU/day for your son. However, after 4 months of that dose, most of the children in both studies only obtained vitamin D levels in the high 30s and lower 40s.

Here is a link to those two studies:

Saad, K. et al. Randomized controlled trial of vitamin D supplementation in children with autism spectrum disorder, Journal of Child Psychology and Psychiatry, and Allied Disciplines, 2018.

Feng, J. et al. Clinical improvement following vitamin D3 supplementation in Autism Spectrum Disorder, Nutritional Neuroscience, 2017.

Both studies found that younger children, like your child, respond better than older children. Also, in my 10-year experience in treating such children, I find that children with the lowest baseline vitamin D level (level before treatment) respond better than children with higher levels. A baseline level of 7 ng/ml – like your son has – improves the likelihood that he will respond.

Both the clinical trials cited above, and my clinical experience, suggest about 75% of autistic children treated with vitamin D will respond. About 1/4 of the children who respond will improve dramatically (autism seems to disappear) and 1/2 will respond significantly, but ¼ of the children will not respond at all. some symptoms will improve, and other symptoms may disappear, but the child still has diagnosable autism.

Remember, vitamin D has numerous co-factors; the four most likely to be needed are magnesium, zinc, vitamin K, boron and zinc. Also, believe it or not, I have written 324 blogs that contain the word, “co-factors.”

Good luck. Please keep in touch and tell me if and how your child improves after vitamin D.


John Cannell, MD

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