The finding came from new research which looked at data on nearly 50,000 people and was published in The Lancet.
Short-term use of folic acid supplements is unlikely to considerably increase or decrease overall cancer risk and has little impact on the risk of developing any specific cancers, such as prostate, colon, lung, and breast.
According to the researchers, this report should reassure people that short-term folic acid intake, either through fortification or from supplements, is actually safe. A prior study in the journal CANCER indicated that folic acid supplements may stop cancer from progressing and promote regression of disease.
Robert Clarke, one of the lead authors and from the University of Of Oxford, UK, said:
"The nationwide fortification of foods involves much lower doses of folic acid than studied in these trials, which is reassuring not only for the USA who have been enriching flour with folic acid to prevent neural tube birth defects (such as spina bifida) since 1998, but also for over 50 other countries where fortification is mandatory (eg, Australia, South Africa, Chile, Argentina, and Brazil)."
Clarke and a team of experts from the B-Vitamin Treatment Trialists' Collaboration analyzed all large randomized trials of folic acid supplementation (with or without B vitamins) up to the end of 2010.
Results from the meta-analysis showed that the subjects who took folic acid every day for at least 5 years did not have a considerably higher chance of developing cancer compared to those who took placebo.
The folic acid groups had 7.7% (1904) new cases of cancer while the placebo groups had 7.3% (1809) new cases.
No notable increase in overall cancer incidence was seen even in the subjects with the highest average intake of folic acid (40 mg per day), the experts explained.
The folic acid and placebo groups showed no considerable difference in the number of subjects who developed lung, breast, colorectal, prostate, or any other type of cancer.
The scientists also found no evidence that taking folic acid for longer periods of time elevated a person's chance of developing cancer.
"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. It remains to be seen whether any beneficial or harmful effects on cancer incidence will eventually emerge with even longer treatment or follow up."
In a linked statement, Cornelia M Ulrich, Director of the National Center for Tumor Diseases and German Cancer Research Center, and Joshua W Miller, from Rutgers University in the USA, noted that it is important to remember the dual relationship of folate and cancer. Although it may protect against cancer development, it can also result in the growth of existing cancer cells.
This is especially significant, they said, 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 (1 mg/day) for total consumption of folic acid."
Written by Sarah Glynn