There are some claims that taking B12 supplements which contain folic acid causes cancer.
Is this true? Are there vitamin B12 supplements without folic acid?
Here's a passage from the book Eat to Live by Dr. Joel Fuhrman
Avoid taking supplements that contain these ingredients: vitamin A, high-dose (200 IU or greater) isolated vitamin E, folic acid, beta-carotene, and copper. Ingesting vitamin A or beta-carotene from supplements instead of food may interfere with the absorption of other crucially important carotenoids, such as lutein and lycopene, thus potentially increasing your cancer risk. (1)
Folic acid is the synthetic form of folate added to food or used as an ingredient in vitamin supplements. Folate is found naturally in fruits, vegetables, grains, and other foods. Too much folate obtained naturally from food is not a concern. It comes naturally packaged in balance with other micronutrients, and the body regulates its absorption. (2)
Everyone, including pregnant women, should be getting adequate amounts of folate from natural plant sources. Recently, there have been some troubling studies connecting folic acid supplementation and cancer. More and more evidence suggests that folic acid supplementation may significantly increase the risk of cancer. (3)
(1) Mayne ST. Beta-carotene, carotenoids, and disease prevention in humans. FASEB J. 1996;10(7): 690–701; Goodman GE. Prevention of lung cancer. Curr Opin Oncol. 1998;10(2):122–26; Kolata G. Studies find beta carotene, taken by millions, can’t forestall cancer or heart disease. New York Times. 1996 Jan 19. Omenn GS, Goodman GE, Thornquist MD, et al. Effects of a combination of beta carotene and vitamin A on lung cancer and cardiovascular disease. N Eng J Med. 1996;334(18);1150–55; Hennekens CH, Buring JE, Manson JE, et al. Lack of effect of long-term supplementation with beta carotene on the incidence of malignant neoplasms and cardiovascular disease. N Eng J Med. 1996;334(18):1145–49; Albanes D, Heinonen OP, Taylor PR, et al. Alpha-tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of baseline characteristics and study compliance. J Natl Cancer Inst. 1996; 88(21):1560–70; Rapola JM, Virtamo J, Ripatti S, et al. Randomized trial of alpha-tocopherol and beta-carotene supplements on incidence of major coronary events in men with previous myocardial infarction. Lancet. 1997;349(9067): 1715–20; Bjelakovic G, Nikolova D, Gluud LL, et al. Antioxidant supplements for prevention of mortality in healthy participants and patients with various diseases. Cochrane Database Syst Rev. 2008 Adr 16;(2):CD007176.
(2) Harvard School of Public Health. The Nutrition Source. Keep the Multi, Skip the Heavily Fortified Foods. http://www.hsph.harvard.edu/nutritionsource/what-should-you-eat/folic-acid/.
(3) Yi K. Does a high folate intake increase the risk of breast cancer? Nutr Rev. 2006; 64(10 Pt 1): 468–75; Cole B, Baron J, Sandler R, et al. Folic acid for the prevention of colorectal adenomas. JAMA. 2007; 297(21):2351–59; Stolzenberg-Solomon R, Chang S, Leitzman M. Folate intake, alcohol use and postmenopausal breast cancer risk in the Prostate, Lung, Colorectal and Ovarian Cancer Screening Trial. Am J Clin Nutr. 2006;83:895–904; Smith AD, Kim Y, Refsuh H. Is folic acid good for everyone? Am J Clin Nutr. 2008;87(3):517; Kim Y. Role of folate in colon cancer development and progression. J Nutr. 2003;133(11) (suppl 1):S3731–39; Guelpen BV, Hultdin J, Johansson I, et al. Low folate levels may protect against colorectal cancer. Gut. 2006;55:1461–66.
Here's another passage by Steven Novella on Vitamins and Mortality. But it seems to contradict with what Joel Fuhrman says.
In the latest issue of The Archives of Internal Medicine is a population based observational study looking at health outcomes and vitamin use as part of the larger Iowa Women’s Health Study. The authors looked at 38,772 older women and asked them to self-report their vitamin use. This is a long term study and their vitamin use was reports in 1986, 1997, and 2004, and mortality was followed through 2008. They found a small but statistically significant increase in mortality for those taking multivitamins, B6, folic acid, iron, copper, magnesium and zinc. There was also a small decrease in mortality for those taking calcium.
The strength of this study is that it is large with a long term follow up. There are many weaknesses, however. Vitamin use was self-reported. Further, this is a correlational study only. Therefore possible confounding factors could not be controlled for. For example, it is possible that women who have an underlying health issue that increases their mortality were more likely to take vitamins or to report taking vitamins.In fact, other studies suggest there is such a “sick-user effect” with vitamins.
It is therefore not possible from this study to draw any conclusions about cause and effect – that vitamin use increases mortality. But it does provide a cautionary reminder that it is not reasonable to assume that vitamin supplementation is without any risk. We still need to follow the evidence for the use of specific vitamins at specific doses for specific conditions and outcomes.