Study raises concerns over multivitamins and prostate cancer

By Stephen Daniells

- Last updated on GMT

Related tags: Prostate cancer, Epidemiology, Cancer

A new study from the US National Cancer Institute has reported that taking excessive amounts of multivitamins may increase the risk of advanced and fatal prostate cancers by 30 per cent.

The study, published in the Journal of the National Cancer Institute​, assessed the diets of 295344 men without prostate cancer, and found that during five years of follow-up men who consumed multivitamins more than seven times a week had increased risks of advanced and fatal prostate cancers, but no effect was observed for early or localized prostate cancer. "These results suggest that regular multivitamin use is not associated with the risk of early or localised prostate cancer,"​ wrote lead author Karla Lawson. "The possibility that men taking high levels of multivitamins along with other supplements have increased risk of advanced and fatal prostate cancers is of concern and merits further evaluation."​ Over half a million new cases of prostate cancer are diagnosed every year worldwide, and the cancer is the direct cause of over 200,000 deaths. More worryingly, the disease's incidence rate is increasing with a rise of 1.7 per cent over 15 years. An independent expert has warned however that the research adds to conflicting evidence on the use of the supplements, while a US-based dietary supplements trade association representative raised questions about the methodology of the results. The researchers investigated the association between multivitamin use and prostate cancer risk on male participants as part of the National Institutes of Health (NIH)-AARP Diet and Health Study. During five years of follow-up, 10,241 participants were diagnosed with incident prostate cancer (8,765 localised cancers and 1,476 advanced). "In this large prospective study, we found that multivitamin use was unrelated to overall risk of total and organ-confined prostate cancer,"​ wrote Lawson. However, in a subgroup of men reporting excessive multivitamin consumption, 32 per cent had a higher risk of advanced and fatal prostate cancers compared to men who did not consume the supplements. "Because multivitamin supplements consist of a combination of several vitamins and men using high levels of multivitamins were also more likely to take a variety of individual supplements, we were unable to identify or quantify individual components responsible for the associations we observed,"​ wrote the researchers. They add that the positive associations with excessive multivitamin use were strongest in men with a family history of the disease, or amongst men who took additional micronutrient supplements, including beta-carotene, selenium, or zinc. The research is at odds with a nested study published recently in The American Journal of Clinical Nutrition​ that reported that an increased selenium intake in combination with a daily multivitamin may reduce the risk of prostate cancer by about 40 per cent. Commenting independently on the research, Liz Baker, science information officer at British charity Cancer Research UK, said: "It's still not entirely clear what factors can affect a man's risk of developing prostate cancer. And there is conflicting evidence on the pros and cons of vitamin supplements. These products don't seem to give us the same benefits as vitamins that naturally occur in our food.​ Baker said that the charity continues to encourage consumers to eat a diet rich in fibre, vegetables and fruit, and low in red and processed meat. The results were challenged by Daniel Fabricant, vice president of scientific and regulatory affairs at US-based trade association the Natural Products Association (NPA). "This is a cohort study, which is not as reliable as the 'gold standard,' a randomized controlled trial,"​ said Fabricant. "As with many cohort studies, there are a large number of variables involved. These missing observations are filled in by the authors' evaluation of the numbers and then the resulting bias, of which there is a great deal in this study. This is why the best studies ask one research question at a time with one clear-cut outcome being measured."[Also], considering what a strong factor family risk is for all cancers, prostate cancer may also increase in men who have a family history of breast cancer. Other potential risk factors of this nature were not accounted for in the study,"​ he said. Source: Journal of the National Cancer Institute​ Volume 99, Issue 10, Pages 754-764; doi:10.1093/jnci/djk177"Multivitamin Use and Risk of Prostate Cancer in the National Institutes of Health-AARP Diet and Health Study"​Authors: K.A. Lawson, M.E. Wright, A. Subar, T. Mouw, A. Hollenbeck, A. Schatzkin, M.F. Leitzmann

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