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.
PRENATAL VITAMINS: WHICH ONES TO TAKE
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:
- This 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 so doctors recommend women to take folic acid before becoming pregnant
- Iodine is critical for a woman's thyroid function
- A deficiency can cause a baby's stunted growth, severe mental disability and deafness
- It can also lead to miscarriage and stillbirth
- Pregnancy increases the risk of becoming anemic
- Iron helps blood carry oxygen to both the mother and baby
- It is critical to support red blood cells, the placenta and the growth of the baby
- Calcium can help prevent a pregnant woman from losing her bone density
- During pregnancy the baby uses calcium for its own bone growth, causing a deficiency in the mother
'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,' said Levine.
Previous studies have linked vitamin deficiency during pregnancy with deficits in neural development in children, leading doctors to recommend folic acid to pregnant women.
Folic acid is a water-soluble B vitamin that can treat anemia and is often used as a prenatal supplement.
The two most common neural tube defects are spina bifida, where the spinal column does not close completely, and anencephaly, and condition where a baby's brain and skull do not fully develop.
Both of those conditions develop within the first few weeks of pregnancy.
Austism refers to a range of developmental disorders that begin in childhood, affecting one in 68 children in the US.
It is three times more common in boys than girls with symptoms including difficulty with social interactions, impaired language and communication skills and unusual behavior.
Those on the autism spectrum may be over-sensitive to sounds, touch, smells and taste and symptoms can range from mild to severe.
Levine said: 'Reduced risk of autism spectrum disorder in offspring is a consideration for public health policy that may be realized by extended use of folic acid and multivitamin supplements during pregnancy.'
However, he added that the findings need to be interpreted with caution because other factors could explain the link.
'Our study could not determine whether this result is due to the vitamin or to unmeasured confounding by other conditions - such as pre-term birth or lifestyle factors,' said Levine
The CDC recommends that all women of childbearing age consume 400 micrograms daily to prevent common and serious birth defects that develop within the first four weeks of pregnancy.