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Folic acid not linked to cancer risk

Louise Prime

Friday, 25 January 2013

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Folic acid supplements or fortification are unlikely to raise cancer risk, confirms the latest research. Authors of the new analysis, published today in The Lancet, say their results provide reassurance about the safety of nationwide fortification, which is practised in many countries – at much lower doses than levels in the trials they analysed.

Researchers in Oxford and elsewhere conducted a meta-analysis of all pre-2011 large studies of supplementation with folic acid, either alone or combined with other B vitamins.

Their analysis showed that new cases of cancer were not significantly more likely to occur in people taking folic acid daily for up to 5 years than they were in people taking placebo (7.7% vs. 7.3%). Even in one study in which people took the highest folic acid dose, 40mg daily, there was not a significantly raised risk of developing cancer.

The researchers did not find a significantly increased risk of any individual cancer site in those taking folic acid; nor did longer duration of folic acid treatment increase cancer risk.

They said their analysis provided reassurance that folic acid supplementation neither increases nor decreases incidence of site-specific cancer during the first 5 years of treatment. They wrote: “Both the hopes for rapid cancer prevention and the fears about rapidly increased cancer risk from folic acid supplementation were not confirmed by this meta-analysis of the trials of folic acid supplementation.”

But they acknowledged that their analysis does “not address the question of whether any beneficial or harmful effects on cancer incidence will eventually emerge among the participants many years after the trials all ended”.

The authors point out that nationwide dietary fortification of flour and other cereal products – for example, the US has been enriching flour with folic acid since 1998 to reduce the incidence of neural tube defects – involves doses of folic acid that are 0.1-0.4mg, an order of magnitude lower than the median doses studied in these trials (2.0mg).

They concluded: “In aggregate, the trials provide no significant evidence of short-term effects of folic acid supplementation on overall cancer incidence, or on the incidence of any particular type of cancer.”

The authors of a Comment on this study pointed out that the modest excess cancer risk shown by the meta-analysis was very close to reaching ‘significance’. But they agreed with the study’s authors that because the daily doses used in studies in this meta-analysis were so much higher than the current level of fortification in the US, this was reassuring for people exposed solely to fortification.

However, they said that it might become relevant for “those who consume excess folic acid from fortification and supplements combined. Notably, 1-4% of the US population, depending on age, sex, and ethnic origin, exceed the tolerable upper limit (1mg/day) for total consumption of folic acid.”

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