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Folic acid supplimentation during pregnancy may increase risk of breast cancerBreast cancer news 3/11/2005 Doctors usually advice folate supplementation during pregnancy to prevent neural tube defects occurring to the fetus. The long term effects of high dose supplementation, such as in pregnancy is largely unknown. Theoretically this high dose supplementation can lead to antimetabolic effects. We do not much information on long term effects of high dose folate intake during pregnancy. New data presented in the British Medical Journal suggests that intake of high doses of folate throughout pregnancy may be more likely to die from breast cancer in later life than women taking no folate. The researchers studied data from June 1966 to June 1967 and identified 3187 women as potentially eligible for a trial of folate supplementation. At patients initial visit, the mother's age, gestation, parity, weight, and blood pressure were recorded, and blood was taken to measure serum folate concentrations. This was a double blinded trial. No women withdrew from the trial. The records were linked with those held by the National Health Service Central Registry in Edinburgh and the cause of death ascertained. In all, 3037 women were recruited to the study, and 2928 were randomised. In the placebo group, 1.9% said that they had not taken their tablets regularly compared with 1.7% in the study group taking 0.2 mg folate and 3.2% in the study group taking 5 mg. Initial folate concentrations were similar in the three groups. Death data was analyzed by the end of September 2002. At that time 210 women had died; 40 deaths were attributable to cardiovascular disease, 112 to cancer, and 31 to breast cancer In women randomised to high doses of supplemental folate, all cause mortality was about a fifth greater, and the risk of deaths attributable to breast cancer was twice as great. This increased risk in deaths attributable to breast cancer is unlikely to be due to competing causes as the number of deaths was small and all cause mortality appeared to be greater. This increase in mortality and in death from breast cancer with high doses of folate could be a chance finding. The number of deaths was small, the confidence intervals were wide, and the author had no prespecified hypothesis that taking folate supplements in pregnancy would increase the risk of cancer. This randomised trial and was of high quality, bias and confounding are unlikely explanations for these findings. A recent study indicated that rats fed diets deficient in folate had increased mammary tumorigenesis compared with rats fed diets with sufficient folate, whereas rats fed a high dose folate diet had similar levels of tumorigenesis to deficient rats. These data are preliminary and these findings require confirmation. What this paper suggests Women taking high doses of folate throughout pregnancy may be more likely to die from breast cancer in later life than women taking no folate What research is needed now This may be a chance finding, so further studies should examine the association between folate supplementation in pregnancy and risk of breast cancer Based on BMJ 2004;329:1375-1376 (11 December), doi:10.1136/bmj.329.7479.1375 |