Excessive Use of Multivitamins May Have Increased Risk of Advanced and Fatal Prostate Cancers

21/05/07 A new US study suggests that men who make excessive use of multivitamins and other supplements may have increased risk of advanced and fatal prostate cancers. The researchers say further research is needed to verify their findings.

The study is published in the Journal of the National Cancer Institute (JNCI).

Multivitamins and dietary supplements are taken every day by millions of American men. Previous studies have suggested there may be a link between multivitamin use and advanced prostate cancer, but the results have been unclear.

A prospective study led by Dr Karla Lawson from the US National Cancer Institute investigated the link between multivitamin use and the risk of prostate cancer in over 295,000 men.

They found that men who took multivitamins more than seven times a week had an increased the risk of advanced and fatal prostate cancer. But there was no link with early or localized prostate cancer, they said.

The participants were enrolled in the National Institutes of Health (NIH) AARP Diet and Health Study and were cancer free at the start of the study in 1995 and 1996. In 5 years of follow up, 10,241 men were diagnosed with incident prostate cancer; this included 8,765 localized and 1,476 advanced cancers.

They also did a separate mortality analysis of the participants over a 6 year follow up period and found 179 cases of fatal prostate cancer.

The participants' use of multivitamins and food supplements was assessed by questionnaire at the start of the study, and data from this survey with the medical results were used to calculate relative risk, taking into account other known prostate cancer risk factors.

The results showed that:

  * There was no significant link between multivitamin use and localized prostate cancer risk.
   * However, men who consumed multivitamins more than seven times a week (classed as excessive multivitamin users) had a significantly higher risk of advanced and fatal prostate cancers (32 and 98 per cent respectively) compared with men who did not take multivitamins at all.
   * Another way to look at the results is incidence rate in person years: for excessive multivitamin users the incidence rate for advanced and fatal prostate cancers was 143.8 and 18.9 per 100,000 person-years, compared with 113.4 and 11.4 in never users.
   * The link with excessive multivitamin use was strongest in "men with a family history of prostate cancers or men who took individual micronutrient supplements, including selenium, beta-carotene, or zinc", the researchers reported.

In conclusion, the researchers suggested that:

"Regular multivitamin use is not associated with the risk of early or localized prostate cancer. 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."

A more rigorous case-controlled study is needed to make sure the differences between heavy multivitamin users and non users are properly taken into account to get a clearer picture of the link between multivitamin use and prostate cancer.

"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 that we observed," the researchers wrote.

In an editorial in the same issue of the journal, Dr Goran Bjelakovic of the University of Nis in Serbia, and Dr Christian Gluud of Copenhagen University Hospital in Denmark, discuss the pros and cons of antioxidant supplements with respect to health and the impact of these new findings by Dr Lawson and her colleagues, which they say:

"Add to the growing evidence that questions the beneficial value of antioxidant vitamin pills in generally well-nourished populations and underscore the possibility that antioxidant supplements could have unintended consequences for our health."

Health and cancer experts advise men seeking to reduce their risk of prostate cancer to eat a balanced diet with plenty of fruit and vegetables, and low in red and processed meats.

Prostate cancer usually occurs in older men. It affects the tissues of the prostate, which is located below the bladder and in front of the rectum in a man's reproductive system.

According to the US National Cancer Institute (NCI), prostate cancer is the most common cancer, excluding skin cancer, and the second leading cause of cancer-related death in American men.

The NCI estimates that in 2007 there will be over 200,000 new cases of prostate cancer in the US, and over 27,000 men will die from it. It occurs more commonly in African American men, and the mortality rate among African American men is double that of American men in other racial or ethnic groups.