Supplements and Cancer

One of the differences between CAM and modern medicine is the quality of the research that has been used to evaluate claims. One example of this is the use of supplements to prevent disease. In their publications, naturopaths almost always point to supplements as  a key element in maintaining good health. It seems to me that many of them jump from  studies that show vitamin and mineral deficiencies cause disease (e.g. hyper- and hypothyroidism and selenium) and jump to the conclusion that supplements will prevent disorders. This is often expanded to include diseases that are not related in any way to the results of a deficiency.

A large scale study begun in 2001 has raised serious questions about the usefulness of two of two common supplements, Vitamin E and Selenium. The Selenium and Vitamin E Cancer Prevention Trial (SELECT) was begun to verify earlier studies that suggested that a decrease in cancer resulted from long term use of these products. However, that is not what was found.

A question and answer form of the results can be found here.

  • In the 2008 report, did the supplements reduce the risk of any disease? 
    No. There was no difference in the incidence of lung or colorectal cancers, all cancers combined, all deaths combined, or the overall incidence of cardiovascular events between the study groups.
  • What is new about the updated (2011) SELECT results? 
    The data published in 2011 include 18 months of additional follow-up information on the participants through July 5, 2011. During this time, SELECT men were no longer taking study supplements. These additional data provide an average of seven years of information on the participants: 5.5 years taking study supplements plus 1.5 years of observation or follow-up.
  • What are the updated (2011) results of SELECT? 
    The additional data show that the men who took vitamin E alone had a 17 percent relative increase in numbers of prostate cancers compared to men on placebo. This difference in prostate cancer incidence between the vitamin E only group and the placebos only group is now statistically significant, and not likely to be due to chance.
  • Men taking selenium alone, or vitamin E and selenium, were also more likely to develop prostate cancer than men taking placebo, but those increases were smaller and are not statistically significant and may be due to chance. Updated results of SELECT were published in JAMA on October 12, 2011 (3).
  • Do we know why an increased risk for prostate cancer was found in 2011 vs. 2008? 
    As with many medications, the actions of vitamin E may last long after the last pill is taken. The differences in prostate cancer incidence between the vitamin E group and the placebo group began to emerge at about the third year of study supplementation (see graph below of cumulative cases)
  • The observation that the risk of prostate cancer has continued to increase suggests that vitamin E may have long-term effects on prostate cancer risk. SELECT researchers will continue to follow the study participants to see whether the increased risk continues with longer time off of the supplements.
  • With this additional information, was there any difference in other cancers or diseases from SELECT supplements? 
    There continue to be no differences in the incidence of lung or colorectal cancers, all cancers combined, all deaths combined, or the overall incidence of cardiovascular events between the study groups. Although initial results showed that more men taking selenium were diagnosed with diabetes, longer follow-up showed no increased risk of this disease.

Besides determining a correlation between Vitamin E supplementats and prostate cancer, the study did not show any benefit in preventing other cancers or cardiovascular disease.

  • Should men not take vitamin E supplements? Should they only take them if they are also taking selenium? There are no clinical trials that show a benefit from taking vitamin E to reduce the risk of prostate cancer or any other cancer or heart disease (2, 3, 5-9). While the men in SELECT who took both vitamin E and selenium did not have a statistically significant increase in their risk for prostate cancer, they also did not have a reduced risk of prostate cancer or any other cancer or heart disease.

Of course, as in any study, it is important to determine who financed the study, as biases may be introduced.

  1. How much did SELECT cost? Who else funded the study, and why? NCI is the primary funding agency for SELECT and has provided $129,687,000 to SWOG from 1999 through 2011, with an additional $4.5 million contributed by the National Center for Complementary and Alternative Medicine (NCCAM), also an agency of the National Institutes of Health (NIH). NCI has also separately funded a substudy to see if the supplements affect the growth of colon polyps. Participants who report having had a colorectal screening procedure while participating in SELECT were asked to sign a consent and release agreement for their medical records. Once all screening procedure reports are collected and reviewed, the researchers will study and report the findings. In addition, ancillary studies were funded by three other NIH institutes:
  1. The National Institute on Aging (NIA) provided almost $7 million for the Prevention of Alzheimer’s Disease with Vitamin E and Selenium (PREADVISE) trial. This trial is evaluating whether these supplements can help prevent memory loss and dementia, such as that found in Alzheimer’s disease. This study closed to accrual in 2009 but PREADVISE participants continuing in centralized follow-up are still being followed.
  2. The National Eye Institute (NEI) provided almost $2 million for the SELECT Eye Endpoints Study (SEE). Age-related macular degeneration (AMD) and cataracts are two leading causes of visual impairment in older Americans. AMD is a disease that affects the central vision, and is the leading cause of visual problems and blindness, with about 25 percent of people over 65 showing some AMD. Cataracts cloud the eye’s lens that causes loss of vision. More than 50 percent of adults in the U.S. age 75 and older suffer from visually significant cataracts.
  3. The National Heart, Lung and Blood Institute (NHLBI) has provided more than $3 million for the Respiratory Ancillary Study (RAS). The overall objective of RAS is to understand whether supplements being studied in SELECT have an impact upon the loss of lung function experienced with aging, which is higher in persons who smoke cigarettes. This study closed to accrual in 2007. Sites that were invited to participate had a higher percentage of current and former smokers than the overall SELECT study. (19-20).

One of the participants was the  National Center for Complementary and Alternative Medicine (NCCAM), whose purpose is to fund studies that support the use of CAM. In this case as in every other study funded by NCCAM, those positive results were not forthcoming.

Will be see a decrease in support of supplements among the CAM community? Don’t hold your breath.


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One Response to Supplements and Cancer

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