TAKING high doses of folic acid during pregnancy may increase the risk of breast cancer, according to a study published today.

The research, involving 3,000 pregnant women, found that in those taking a 5mg supplement of folate, the risk of deaths from breast cancer was twice as great compared with those taking a dummy pill.

But the researchers said it may be a chance finding. Other studies have suggested folic acid could reduce the risk of breast cancer.

Campaigners said women should continue to take the supplements as recommended by the Department for Health and the small numbers involved in the new study were not statistically significant.

This advice was endorsed by Dr Bill Kirkup, director of public health for the North-East. He said: "It would be a great shame if people gave up taking something that is so beneficial."

Women trying for a baby are advised to take a daily 0.4mg supplement of folic acid before conception, and for the first 12 weeks of pregnancy, in order to reduce the risk of neural tube defects such as spina bifida.

However, the latest study, published in the British Medical Journal, looked only at women given 0.2mg or 5mg doses, with the majority of women starting to take the supplements after 12 weeks and until the end of their pregnancy.

The researchers, from the universities of Bristol and Aberdeen, followed the women from the 1960s until September 2002.

During this time, 210 women died, with 40 deaths due to cardiovascular disease, 112 due to cancer and 31 to breast cancer.

The researchers said: "In women randomised to high doses of supplemental folate, the risk of deaths attributable to breast cancer was twice as great."

But researcher Dr Andy Ness said: "Our paper presents preliminary findings which are intended to point the way towards further research and it is published on that basis. It is entirely possible that this is a chance finding, so further scientific studies are required to examine the association, if there is one, before we reach any conclusions."

He said it was important not to confuse women about the need to take folic acid supplements early in pregnancy.

"Women planning to become pregnant should take supplements as recommended as there is a considerable difference between the trial and the current guidelines to prospective mothers," Dr Ness added.

Su Dixon, a National Childbirth Trust representative from Northallerton, North Yorkshire, said: "Having a baby with spina bifida is a real risk now, whereas this research only suggests there may be an increased risk of breast cancer in the future."