Vitamins may not prevent cancer

Friday November 7th, 2008

New findings cast fresh doubt on claims that folic acid, vitamin B6, and vitamin B12 may play a role in cancer prevention.

Dr Shumin Zhang of Brigham and Women's Hospital, Boston, USA, and colleagues looked at the effects of daily supplementation with these vitamins on 5,442 women aged 42 or above with a pre-existing risk of cardiovascular disease.

Participants received either the supplement or placebo for an average of 7.3 years. During this time, 379 of the women developed invasive cancer. Women taking the supplement had a similar cancer risk to those on placebo, report the team in the Journal of the American Medical Association.

They write: "Background fortification of the food supply with folic acid (a synthetic form of folate), a policy that began in the United States in 1998 to reduce risk of neural tube defects, has improved folate status in the general population.

"Approximately one-third of US adults currently take multivitamin supplements containing folic acid, vitamin B6, and vitamin B12."

However, "combined folic acid, vitamin B6, and vitamin B12 treatment had no significant effect on overall risk of total invasive cancer or breast cancer among women during the folic acid fortification era".

The researchers add that there may be some benefit of taking combined B vitamins for women aged 65 years or older, but not for younger women.

"This finding is biologically plausible because elderly individuals have increased requirements for these B vitamins," they write. "If the finding is real and substantiated, the results may have public health significance because the incidence rates of cancer are high in elderly persons."

Zhang, S. M. et al. Effect of Combined Folic Acid, Vitamin B6, and Vitamin B12 on Cancer Risk in Women: A Randomized Trial. The Journal of the American Medical Association, Vol. 300, November 5, 2008, pp. 2012-21.

Tags: Cancer | North America | Nutrition & Healthy Eating

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