Autism and vitamin D: is there a link?

Diagnoses of autism have increased all over the world. Rates have risen in particular since the 1990s, but it is very difficult to say if this is truly due to more children having autism, or whether we’ve got better at recognising it early and testing for it. We’ve also broadened the term to include an umbrella of conditions known collectively as autistic spectrum disorder (ASD), where previously Asperger's syndrome and others would have been considered a separate condition.

It should also be made clear that while all people with autism have certain difficulties in common, it will also affect them in different ways and to different levels of severity. While the label can be helpful in accessing help, and understanding one’s feelings and difficulties, it by no means defines someone, or their journey through life.

Vitamin D deficiency is prevalent, particularly in parts of the world where exposure to sunlight is limited. Researchers have looked at whether low vitamin D levels in mothers during pregnancy can increase the risk of a child developing autism. One study measured vitamin D in mothers’ blood during pregnancy, and another study measured vitamin D levels in the babies' blood five days after birth.

Both found an increased risk of developing autism where low vitamin D levels were present. To be clear, this does not mean that low vitamin D causes autism, only that its presence is linked with an increased likelihood of autism than in children born with normal vitamin D levels.

There is ongoing research into this question and sadly there is still no clear answer. A study has been conducted by giving mothers who have a child with autism vitamin D supplements during pregnancy. It showed some positive results in reducing the incidence of autism in newborn siblings, however this was a very small study without a control group or blinding, two key features used in more defining research. At this time it is unclear how much can be taken from this.

There are people who advise giving vitamin D to promote development and changes in autistic behaviour. However a small randomised controlled trial in Ireland in 2017 found no significant improvement, after giving vitamin D supplements over a 20-week period.

This area requires continued research, but it's true that vitamin D rates are lower in children with autism when compared to children without autism. Vitamin D is low cost and low risk, and it’s recommended for all children in the winter months, and some ethnicities all year round. So it should be given strong consideration to optimise general health in children with autism. Additionally, vitamin D is safe to take in pregnancy and actually recommended, for other known health benefits, so it's an added bonus if it is protective against autism.

• Written by Dr Tom Maggs, General Manager at Healthwords and Paediatrician