However, in younger women no protective or harmful effects were observed, according to results published in this week’s Journal of the American Medical Association (JAMA).
Over 5,000 women at a high risk of cardiovascular disease took part in the study, which investigated the effects of a daily supplement of folic acid, vitamin B6 and B12 on cancer risk.
“If the finding [that cancer risk in women over 65 is decreased] is real and substantiated, the results may have public health significance because the incidence rates of cancer are high in elderly persons. The finding is biologically plausible because elderly individuals have increased requirements for these B vitamins,” wrote lead author Shumin Zhang from Brigham and Women’s Hospital and Harvard Medical School.
Folate, vitamin B6, and vitamin B12 are thought to play an important role in cancer prevention. This is because the vitamins play an important role in maintaining the integrity of DNA and regulating gene expression, both critical processes in healthy cell function.
Another positive to take from the results is that they appear to support the safety of B vitamins, and particularly folic acid. Since 1998 the US has required mandatory fortification of all grain products with folic acid - the synthetic, bioavailable form of folate - in order to reduce the incidence of neural tube defects (NTD) - most commonly spina bifida and anencephaly.
However, some concerns had been raised that excess folic acid may increase the risk of cancer amongst certain sections of the population. The new study appears to allay these fears.
Zhang and co-workers looked at the risk of cancer and B-vitamin consumption aming the 5,442 participants (average age 62.8) of the Women’s Antioxidant and Folic Acid Cardiovascular Study. The women either had cardiovascular disease or three or more coronary risk factors.
Over the course of 7.3 years, half of the women received a daily supplement of folic acid (2.5 mg), vitamin B6 (50 mg), and vitamin B12 (1 mg), while the other half of the women received a placebo. The study began in 1998 - the same year as mandatory folic acid fortification was introduced in the US.
During the study, 379 case of invasive cancer were diagnosed - 187 in the B-vitamin group and 192 in the placebo group. No differences in the risk of developing total invasive cancer or breast cancer, when the participants were viewed in their entirety.
However, in women over the age of 65 the supplementation was associated with significant 25 and 38 per cent reductions in the risk of invasive and breast cancer, respectively.
The researchers state that the observation may be due to chance.
To fortify or not to fortify
Since the study was started after the introduction of mandatory folic acid fortification, there is the suggestion that any beneficial effects may have been more difficult to observe, and that cancer risk reduction may occur in populations with a lower folate status. However, Zhang and co-workers note that a Norwegian study also reported null findings for B vitamins and cancer. Norway does not have the fortification policy.
" To our knowledge, the WAFACS trial also had the longest duration of treatment with combined B vitamins of any trial to date, high follow-up rates, and relatively high adherence to treatment. Women have been underrepresented in other B vitamin trials, and the WAFACS trial is the largest trial of women," wrote the researchers.
Source: Journal of the American Medical AssociationNovember 4, 2008, Volume 300, Issue 17, Pages 2012-2021" Effect of Combined Folic Acid, Vitamin B6, and Vitamin B12 on Cancer Risk in Women" Authors: S. M. Zhang, N.R. Cook, C.M. Albert, J.M. Gaziano, J.E. Buring, J.E. Manson.