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A research team based at several academic institutions in Korea has found that women with a high intake of folate were 66% and 70% less likely to suffer from cancer of the colon and rectum, respectively. Close scrutiny of the data collected from 596 men and women with colorectal cancer and a similar number of matched controls who were free of the disease, showed that a similar benefit was not seen in men.
Folate is a B-vitamin found in green leafy vegetables and legumes such as chick peas and lentils. Folate deficiency has been linked to neural tube defects in infants, so that in several countries including the USA and Canada mandatory fortification programmes are in place. In May 2007 the UK’s Food Standards Agency Board agreed unanimously that 'mandatory fortification' with folic acid should be introduced, alongside controls on voluntary fortification and advice on the use of supplements. But subsequently the publication of two studies which suggested that folic acid might increase the risk of colorectal cancer (CRC), brought plans for fortification to a standstill.
The study by Kim et al., published in the European Journal of Clinical Nutrition (online 24/06/09, doi: 10.1038/ejcn.2009.37) showed that participants with CRC were likely to have a family history of the disease amongst close relatives, to consume more alcohol, be smokers and be less likely to participate in vigorous exercise. In the overall data for men and women combined, when comparing the highest quartile of dietary folate intake with the lowest, those with the highest intakes were found to be 53%, 58% and 52% less likely to develop colorectal, colon or rectal cancers. However, when the data were analysed by gender, they showed that only in the women was there an inverse relationship between dietary folate intake and a reduction in colon and rectal cancers.
Discussing the current work in NutraIngredients.com (06/07/09) Stephen Daniells mentions that whilst the vast majority of studies show folate has a protective effect against colorectal cancers, a few studies have linked folic acid intakes to an increased risk of the disease. A possible explanation of the contradictory results may lie in the difference between the synthetic and natural forms of the vitamin. Folic acid is not a naturally occurring form although it is used by food and pharmaceutical companies for fortification and in supplements. In an article in the April 2009 issue of Nutrition Reviews, Dr Joel Mason from the USDA Human Nutrition Research Center on Ageing at Tufts University explored this subject in greater depth. He indicated that although folic acid was converted to 5-methyltetrahydrofolate, the natural form of the vitamin, it is possible that high oral doses of folic acid may overwhelm this conversion pathway, leaving measureable doses of folic acid in the blood. Therefore, in the presence of pre-cancerous or cancerous tumours, the excess folic acid may actually facilitate the promotion of cancer.
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