Pregnant women with low levels of the vitamin Folate in their blood are more likely to have a baby with a low birth weight, British scientists said on Friday.

Folate is a B vitamin found in green leafy vegetables, cereals and liver. It is essential for foetal growth and gene expression, helping produce and maintain new cells.

Women are already advised to take folic acid supplements, a synthetic compound of folate, before conceiving and during the early months of pregnancy, to reduce the risk of defects such as spina bifida, a defect of the spinal column.

Researchers from the University of Newcastle upon Tyne examined folate levels in red blood cells for nearly 1,000 pregnant women and looked at lifestyle data.

They found higher folate levels in women were associated with increased birth weight for their babies - a marker for good health in infancy and later in life.

“Low folate status in early pregnancy has been linked with low infant birth weight. Mothers with low levels of folate have lighter babies,” said Dr. Caroline Relton, who headed the research team.

Babies with low birth weight - 5.5 pounds (2.5 kg) or less - are more likely to have a low IQ and to suffer from health and developmental problems.

Relton and her team, who reported their findings in the British Journal of Nutrition, also noted that women who smoked tended to have lower levels of folate in their blood, which could explain why they give birth to smaller babies.

The researchers believe their findings strengthen the argument for fortifying foods such as bread and cereals with folic acid.

The United States started fortifying flour with folic acid several years ago after its role was established in reducing neural tube birth disorders. Other countries included Canada, Australia, Mexico and Chile have followed their example.

These birth defects occur during the early development of the fetus, when the spine does not close properly. Spina bifida is the most common of these. Since the United States began the fortification program the number of babies born with spina bifida or another serious defect called anencephaly has fallen.

Scientists have also found that daily supplements of folic acid or food fortified with it can help to prevent heart disease, stroke, blood clots and cognitive decline.

However, folic acid breaks down a substance called homocysteine in the blood, and too much homocysteine is related to a higher risk of heart attack and stroke.