Folic acid supplements do not raise people's risk of developing cancer, according to an important new study in the Lancet medical journal.
A large new analysis of existing research has confirmed the safety of taking folic acid supplements.
Folic acid is particularly important for women of child-bearing age, as it helps to prevent neural tube defects such as spina bifida.
Unfortunately, it is rarely consumed in adequate amounts from dietary sources, so health experts advise women to take 400 micrograms of the nutrient every day while trying to conceive and during the first 12 weeks of pregnancy.
A large number of trials have been carried out to assess the supplement's safety and a meta-analysis of studies involving almost 50,000 individuals has now shown that it is not associated with an increased risk of cancer.
Scientists at Oxford University found that people who take a daily folic acid supplement for five years or less are not significantly more likely to develop cancer - including bowel, prostate, lung and breast cancer - than those who do not use the supplement.
The findings are published in the Lancet medical journal and provide "reassurance about the safety of folic acid intake, either from supplements or through fortification, when taken for up to five years", according to Dr Robert Clarke, one of the study's lead authors.
Although the study did not look at the effects of longer-term supplementation, the researchers noted that there was no evidence that folic acid users' risk of developing cancer increased over time.
Dr Clarke concluded that fears about a link between folic acid supplementation and increased cancer risk "were not confirmed by this meta-analysis".
The findings are good news for those using folic acid supplements, but it is possible to obtain enough folic acid in the form of folate from dietary sources.
People who wish to boost their intake of this vital nutrient should focus on certain foods, such as broccoli, Brussels sprouts, spinach, asparagus, peas, liver, chickpeas and brown rice.
In addition, the way these foods are prepared can make a big difference to the amount of folic acid you actually get, with experts advising people to steam the above vegetables to prevent their folate content from being depleted as they are cooked.