TAKING folic acid or multivitamins during or before pregnancy slashes the risk of children developing autism by almost three- quarters, research has revealed.

A study of more than 45,000 youngsters found those whose mothers had used the supplements were 73 per cent less likely to develop it.

The finding follows research last year that also suggested they have a protective effect – and could have “important public health implications”.

Interestingly, maternal exposure to either folic acid, multivitamins or both up to two years before pregnancy also reduced the risk by 61 per cent.

Professor Stephen Levine, of Haifa University, Israel, said the phenomenon could be down to a process known as “epigenetic modifications”.

These are alterations in gene expression that can’t be explained by changes in the genetic sequence, so are caused by environmental factors such as diet.

Mr Levine said: “Maternal folic acid and/or multivitamin supplement exposure before and during pregnancy reduced the risk of autism spectrum disorder in offspring.”

The results are consistent with those from a Norwegian study showing maternal folic acid use from four weeks before and eight weeks into pregnancy protects against autism.

Mr Levine added: “This interval is considered relevant to the development of the central nervous system, includes neural tube closure, and is implicated in the development of basic brain structures.”