Women who take multivitamins and folic acid during or before pregnancy cut the risk of their children developing autism by nearly three quarters, according to new research.
A study of more than 45,000 children whose mothers had taken supplements were 73 percent less likely to be on the autism spectrum.
Mothers who consumed the supplements up to two years before pregnancy also reduced the risk of the developmental disorder in their children by 61 percent.
The research highlights the importance of a healthy diet especially before pregnancy as serious fetal defects develop in the first three weeks of gestation - often before women know they are pregnant.
Women who take folic acid and multivitamins are 73 percent less likely to have a child on the autism spectrum, according to researchers from Haifa University in Israel
The study from Haifa University in Israel followed 43,500 Israeli children born between 2003 and 2007 until 2015.
The findings published in JAMA Psychiatry is the first to look for a link between multi-vitamin exposure and autism for an extended period before pregnancy.
Study author Professor Stephen Levine said: 'Maternal exposure to folic acid and multivitamin supplements before and during pregnancy is associated with a reduced risk of autism spectrum disorder in the offspring compared with the offspring of mothers without such exposure.'
Levine said the phenomenon could be due to a process known as epigenetic modifications.
These are alterations in gene expression that can't be explained by changes in the genetic sequence, meaning they are caused by environmental factors such as diet.
The results are consistent with those from previous studies that show taking folic acid from four weeks before and eight weeks into pregnancy protects against autism.
Taking vitamins during and before pregnancy is useful to cover any nutritional gaps in a mother's diet.
Aside from multivitamins that provide a wide range of nutrients, certain supplements offer specific benefits:
Folic AcidThis is a water-soluble B vitamin that helps protect a fetus from developing serious birth defects Many of these defects occur within the first 28 days of pregnancy