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People taking high doses of the B vitamin folic acid are not at an increased risk of cancer, according to an international analysis – easing some concern about the possible side effects of programmes in North America aimed to raise intake of the vitamin.
The US and Canada have required flour to be fortified with folic acid since 1998, after deficiencies of it in pregnant women were tied to brain and spinal cord birth defects in their babies.
But fortification is not required in Western Europe, for example, partly out of concern that the extra folic acid might slightly increase people’s risk of cancer due to its role in cell growth. Cells, including cancer cells, need folate – the natural form of folic acid – to grow and divide.
Folic acid is also naturally found in spinach, asparagus, lettuce and other greens
“Folic acid supplementation does not substantially increase or decrease incident of site-specific cancer during the first five years of treatment,” researchers wrote in The Lancet.
“Fortification of flour and other cereal products involves doses of folic acid that are, on average, an order of magnitude smaller than the doses used in these trials.
For the analysis, the researchers combined data from 13 separate trials that randomly assigned participants to daily folic acid or a vitamin-free placebo and recorded who went on to develop cancer.
The studies included a total of close to 50,000 volunteers who were followed for just over five years, on average.
During that time, 7.7 per cent of people in the folic acid groups, and 7.3 per cent in the placebo groups, were diagnosed with any kind of cancer, a difference that could have been due to chance, researchers said.
Likewise, there was no increased risk of individual cancers – including colon, prostate, lung or breast cancer – attributed to folic acid.
Most trials used daily doses of folic acid between 0.5 and five milligrams. In the one study that used a much larger dose, 40mg daily, there was still no difference in cancer diagnoses.
The total daily amount of folic acid through flour fortification is less than 0.5mg a day for most in the US. Folic acid is also naturally found in spinach, asparagus, lettuce and other greens, with a recommended daily upper limit of 1.0mg.