Do vitamin supplements increase cancer risk?

Posted on Mon, 20 Apr 15

The media have widely reported that vitamin supplements are linked to an increased cancer risk, but this is a case of alarmist and irresponsible reporting.

Across several media channels today, including the ABC, BBC, Sky News, and several newspapers headlines proclaim that a new study has linked vitamins supplements to cancer.

The study is not actually a new study per se; it is an analysis of old research that was presented at annual meeting of the American Association for Cancer Research. Importantly, the study details have not been released yet, and the media is basing their reports on a short press release (1).

The “study” claims to have reviewed previously published research and found that vitamin supplements are linked to increased cancer risk. Specific details of their findings are not given, but they cite the link between high dose beta-carotene and increased lung cancer in smokers as an example (this research is over 20 years old). And generally suggest that people should avoid vitamin supplements and get all the nutrients they need from food. 

It is not clear what dietary supplements or population groups were included in the review, or what studies they reviewed. 

Commentary:

Suboptimal intakes of vitamins and minerals are common in the general population because of unhealthy eating, nutrient losses though food processing and storage and increased nutritional requirements due factors such as alcohol use, chronic diseases and increasing age (2). For this reason, leading experts recommend nutritional supplements such as a daily multivitamin as part of a healthy diet and lifestyle (3).

The link between vitamin and mineral supplement use and cancer has been investigated previously, with a recent systematic review and meta-analysis of 21 randomized controlled trials, comprising some 91,000 individuals, finding that multivitamin supplements did not increase risk for cancer (4).

And a number of recent large-scale studies have found protective effects. In a study of some 43,000 women conducted by Harvard School of Public Health multivitamin use was associated with reduced risk of colorectal adenoma (5), another important report found multivitamin use was associated with a 30% lower risk of breast cancer related deaths in postmenopausal women with invasive breast cancer (6), and a large prevention study (the Physicians Health Study II) found that daily multivitamin supplementation significantly reduced the risk of total cancer incidence in men (7).

And while it has long been known that high-dose beta-carotene may increase cancer risk in smokers, other individual vitamins such as vitamin D have been associated with important preventative effects in the general population (8). Vitamin D is a dietary supplement that is widely used because deficiency is very common, and the consequences of deficiency can be severe.

Headlines proclaiming that “vitamin supplements are linked to cancer,” based on this press release are an alarming example of irresponsible reporting. Without access to the actual study the media cannot ensure the credibility of their news. And portraying all vitamin supplements as dangerous could have serious adverse effects as vitamins are used to prevent and treat a variety of important health issues. 

This reporting also fails to take into account existing knowledge in this area; namely that vitamin supplements are a well-established and safe way to ensure optimal nutrition and ignores published research suggesting vitamin supplements do not generally increase cancer risk and, to the contrary, may have important preventative effects.

References:

1. Public Release: 20-Apr-2015 Dietary supplements shown to increase cancer risk. University of Colorado Denver.
2. Fairfield KM, Fletcher RH (2002) Vitamins for chronic disease prevention in adults: scientific review. JAMA 287: 3116–3126
3. Ward E. Addressing nutritional gaps with multivitamin and mineral supplements. Nutr J. 2014 Jul 15;13:72.
4. Macpherson H, Pipingas A, Pase MP. Multivitamin-multimineral supplementation and mortality: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2013;97:437–44.
5. Massa J, Cho E, Orav EJ, Willett WC, Wu K, Giovannucci EL. Long-term use of multivitamins and risk of colorectal adenoma in women. Br J Cancer. 2014 Jan 7;110(1):249-55. doi: 10.1038/bjc.2013.664.
6. Wassertheil-Smoller S, McGinn AP, Budrys N, Chlebowski R, Ho GY, Johnson KC, Lane DS, Li W, Neuhouser ML, Saquib J, Shikany JM, Song Y, Thomson C. Multivitamin and mineral use and breast cancer mortality in older women with invasive breast cancer in the women's health initiative. Breast Cancer Res Treat. 2013 Oct;141(3):495-505.
7. Gaziano JM, Sesso HD, Christen WG, Bubes V, Smith JP, MacFadyen J, Schvartz M, Manson JE, Glynn RJ, Buring JE. Multivitamins in the prevention of cancer in men: the Physicians' Health Study II randomized controlled trial. JAMA. 2012 Nov 14;308(18):1871-80.
8. Moukayed M, Grant WB. Molecular link between vitamin D and cancer prevention. Nutrients. 2013 Sep 30;5(10):3993-4021.