Deadly Multivitamins - Supplement Hit Job #42
And on it goes. The latest salvo against nutritional supplements is a new study published in the Journal of the National Cancer Institute that suggests men taking “excessive” multivitamins are at increased risk for advanced and fatal prostate cancers.
Specifically, researchers found that men who took multivitamins more than 7 times a week had a 32% and 98% greater risk of developing advanced and fatal prostate cancers, respectively.
Advanced prostate cancer is certainly serious condition, but let us count the ways why the results of this study should not be of significant concern:
- No association was observed between multivitamin use and overall prostate cancer risk.
- No association was observed between multivitamin use and localized prostate cancer risk. With regular screening (prostate specific antigen - PSA & digital rectal exam - DRE) now much more common, the vast majority of prostate cancers are caught at a localized, early stage. Many treatment options are available and prognoses are good in such cases. In fact, most older men, and many younger men, have cancerous cells in their prostates. Yet, since the cancer is often slow growing, those affected individuals identified through screening often go on to die years later from another condition.
(Just to be clear, I’m not trivializing prostate cancer and its potential effects. It is the most common form of cancer affecting men, and more aggressive forms of prostate cancer, although infrequent, can be deadly. Regular screening and accurate diagnosis are important.)
- The numbers of people in the study affected by either advanced or fatal prostate cancer were small, whether they were taking multivitamins or not. For perspective sake, note that of the nearly 300,000 people included in the study, only 1,476 men, or about 1 out of 200, were diagnosed with advanced prostate cancer. And, in a 6-year follow-up, only 179 cases of fatal prostate cancer were identified. That’s less than 1 out of 1,600 men.
- Separating out the risk of a single factor like multivitamin use is nearly impossible in an observational cohort study such as this one. There are so many potential variables that may impact cancer risk in the studied population. Thus, the results of the study are extremely subject to which variables the researchers choose to identify and adjust for.
For example, family history of prostate cancer is a significant risk factor for the disease. In fact, the researchers observed that the positive association between multivitamin use and aggressive prostate cancer was strongest in individuals with such a family history.
- The study used self-reported food frequency questionnaires (FFQs) to ask study participants about supplement usage. FFQs are subject to significant error, as participants may over- or under-report supplement use.
- As an observational study, it is not nearly as rigorous as an intervention study (where one variable is changed and study participants are given the same substance). Given the potential for variance in the actual nutrients and the levels contained in the different multivitamins actually taken, making comparisons and drawing conclusions is difficult at best.
- Who is suggesting to take multivitamins more than 7 times a week? Ideally, a multivitamin would be taken once per day, along with a set of complementary preventive supplements that suggest a potential protective effect against developing prostate cancer. You can read more about getting help putting together such a program here.
- Frankly, I’d be much more worried about a deficiency in some of the key nutrients like vitamin D, selenium, vitamin E, omega-3 fats, etc. A recent study suggested that prostate cancer risk may be as much as 40% lower for individuals with higher than average selenium intake and either a) higher than average vitamin E intake or b) multivitamin use. Also, the evidence for vitamin D’s preventive potential in cancer is large and growing.
Bottom Line
This most recent study from the National Cancer Institute is just one data point, and not a very sound one at that. For all of the reasons above, it’s amazing that such a study was actually published in such a prestigious journal. If you’re taking a multivitamin as part of an overall dietary and supplement program for prostate health, there is no need to stop doing so based on the results of this study.
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June 22nd, 2007 at 2:42 am
[…] Last month, I wrote a post questioning the conclusions of a poorly designed National Cancer Institute study that suggested taking “excessive” multivitamins could increase your risk for prostate cancer. […]