Researchers from Norway have reported that folic acid and B12 supplements in patients with ischemic heart disease increase the risk of cancer and all-cause mortality. The details of this study appeared in the November 18, 2009 issue of the Journal of the American Medical Society.[1]

Observational studies have shown that diets rich in fruits and vegetables are associated with a lower risk of some cancers. However, most studies of exogenous administration of vitamins have failed to show a protective effect against the development of cancer. The notable exception to this is large doses of exogenous vitamin D, which appear to have a protective effect against the development of colorectal adenomas, pancreatic cancer, and possibly breast cancer.

Exogenous vitamin supplements have on occasion been found to be harmful. For example, researchers affiliated with the Cochrane Hepato-Billary Group have reported that treatment with beta carotene, vitamin A, and vitamin E may increase mortality. Folic acid and vitamin B12 have not been associated with an increased risk of developing cancer. However, in patients with cancer, folic acid can increase the rate of cell division and could enhance tumor growth. In the United States, but not in Norway, folic acid is added to food, giving Americans a higher baseline folic acid level than Norwegians.

The current study evaluated the effects of folic acid and vitamin B12 supplementation in 6,836 patients with ischemic heart disease involved in two separate randomized trials. Patients were randomly allocated to receive 38 months of treatment with the following:        

• Folic acid plus vitamins B12 and B6
• Folic acid plus vitamin B12
• Vitamin B6
• Placebo

These authors made the following observations after 6.5 years:

• 10% of patients receiving folic acid and vitamin B12 developed cancer compared with 8.4% of patients not receiving folic acid and vitamin B12.
• 4% of patients receiving folic acid and vitamin B12 died from cancer compared with 2.9% of patients not receiving folic acid and vitamin B12.
• 16.1% of patients receiving folic acid and vitamin B12 died from any cause compared with 13.8% of patients not receiving folic acid and vitamin B12.
• Vitamin B6 was not associated with any adverse effects.
• Lung cancer accounted for most of the overall increase in cancer incidence in patients receiving folic acid and vitamin B12. Other increased cancers were colorectal, prostate, and hematologic malignancies.

Comments: An editorial in the same issue of JAMA discussed the implications of this study:[2]

They stressed the importance of long-term versus short-term observations. They also suggested that this study does not nullify the importance of folic acid food fortification in this country, which yields much lower levels of folic acid than was present in the Norwegian study. They also stressed the importance of eating a healthy diet, avoiding weight gain, and not smoking for the prevention of cancer. However, these and other studies point out the hazards related to giving large doses of vitamins in hopes of improving health.

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