Maybe. There are no studies on it, even animal studies.
So, to many scientists that means don’t try it. However, scientists do not take care of patients, physicians do that. And, the standard of care for physicians has always been the relative weight of potential to help/danger to patients.
Your 5-year- old may well be on the autism spectrum. At least three clinical trials have shown vitamin D helps established autism. Vitamin D is safe; we have known, or should have known, it is safe since 1999 when Professor Reinhold Vieth’s paper “Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety”. This paper is free in its entirety. New employees of the Vitamin D Council must read it twice.
Yes, give your daughter vitamin D. Start with a vitamin D blood test then begin 150 IU/pound/day. Obtain another 25(OH)D in two months. Adjust the dose until her 25(OH)D is around 70-80 ng/ml.
I outlined my recommendations in my book, “Autism Causes, Prevention and Treatment: Vitamin D Deficiency and the Explosive Rise of Autism Spectrum Disorder,” published by Sunrise River Press.