May 30, 2007

A healthy diet, one rich in the vitamins and trace elements provided by fruits and vegetables, has long been associated with delaying the effects of aging and reducing the risk of cancer and other life-threatening diseases. But what about dietary supplements? What role do vitamin supplements play in boosting longevity or staving off chronic illness? So far, research has been inconclusive; however, two recent studies sound a cautionary note.

Multivitamins and Prostate Cancer
According to the results of a study published in the Journal of the National Cancer Institute (16 May 2007), men who take high doses of multivitamins (more than 7 times a week) may be increasing their risk of dying from prostate cancer. Although senior researcher Dr. Michael F. Leitzmann cautions that "no conclusions can be drawn about cause and effect" from this "observational study," it suggests the need for further research into the exact association between vitamin supplements and the risk of more rapid prostate cancer progression.

Researchers analyzed data from 295,344 men participating in the National Institutes of Health-American Association of Retired Persons Diet and Health Study. These men were cancer free when they enrolled in the study in 1995 or 1996. Looking at data collected during five to six years of follow-up, researchers found no association between multivitamin use and the risk of localized prostate cancer. However, they did discover an increased risk of advanced and fatal prostate cancer among men who reported using high doses of multivitamins. Taking a multivitamin more than 7 times per week was associated with an approximately 30 per cent increased risk of advanced prostate cancer and a near doubling of the risk for fatal prostate cancer.

Daily multivitamin use did not appear to increase the risk of developing prostate cancer, and, even taking higher doses of multivitamins (more than 7 times weekly) was not associated with an increased risk of developing early stage (localized) prostate cancer.

The study also found no evidence to support the idea that taking a multivitamin, at any dosage, helped prevent prostate cancer.

Researchers recommend that you

• Follow a healthy diet to get nutrients,
• Do not exceed recommended doses, if you choose to take a multivitamin, and
• Consult your medical team regarding the role of diet and dietary supplements in your treatment if you have prostate cancer.

(Click to read the article "Multivitamin Use and Risk of Prostate Cancer in the National Institutes of Health - AARP Diet and Health Study.")

Antioxidants and Health
An earlier study, which appeared in the 28 February 2007 issue of the Journal of the American Medical Association, also warned of a potential downside to taking dietary supplements, at least for people who are generally well nourished.

Researchers led by Dr. Christian Gluud of Copenhagen University Hospital in Denmark analyzed 68 studies involving more than 232,000 people and found no firm evidence that taking the antioxidants beta-carotene, vitamin A, vitamin E, vitamin C, or selenium extended life.

In fact, when researchers eliminated "high-bias" studies and considered only the more trustworthy ones (47 studies involving almost 181,000 people), their analysis indicated that taking the supplements beta-carotene, vitamin A, or vitamin E may increase mortality. With vitamin E, the risk of dying rose 4 per cent; with beta-carotene, 7 per cent; and with vitamin A, 16 per cent. "As to vitamin C and selenium, the verdict is still out," writes Gluud in an article entitled "Surviving Antioxidant Supplements."

It is important to remember that researchers did not consider cause of death when analyzing this data and that this study, like the first one described, is based on a statistical review of previously conducted research.

(Click for an abstract of the article "Mortality in Randomized Trials of Antioxidant Supplements for Primary and Secondary Prevention.")