Supplements Not Recommended for Primary Cancer Prevention

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Experts at the American Institute for Cancer Research (AICR) announced mid-February that whole foods, and not dietary supplements, play a role in lowering cancer risk. Citing a huge and comprehensive AICR report on cancer prevention, the panel of experts cautioned against relying on pills and powders as a means of protection. “When the panel examined the accumulated evidence from almost 50 different supplement trials, cohort studies and case-control studies, the results were simply too inconsistent to justify using supplements to protect against cancer,” said AICR Nutrition Advisor Karen Collins, MS, RD

Under certain conditions, some high-dose supplements seemed protective at specific doses, some did nothing, and some actually increased the risk of cancer. In contrast, the research was much more consistent when the AICR expert panel examined over 440 studies on cancer risk and foods that contained specific vitamins, minerals and phytochemicals. These widely different results led them to conclude: “Dietary supplements are not recommended for cancer prevention.”

Collins noted, however, that in the AICR Expert Report, Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective, the panel explicitly states that supplements can have a place in a healthy diet. Certain groups – such as women of child-bearing age – may even receive health benefits from taking controlled doses of specific dietary supplements. But according to the report, lower risk of cancer should not be considered one of those benefits.

“Let’s be clear: although some people have misread the recommendation as simply, ‘Don’t take supplements ever,’ that’s not what the expert panel concluded,” said Collins. “The panel members were careful to make an important distinction, namely: Don’t rely on supplements to protect you from cancer.”

When the AICR expert panel reviewed the accumulated data from supplement studies, they noted that much of the research showing high-dose dietary supplements influencing cancer risk was conducted among people who were already at high risk for cancer. That means the results from these studies may or may not extend to the rest of the population. The panel concluded that there is no way to reliably predict the risks and benefits that widespread use of such supplements could produce, and the potential for unexpected and unfavorable side effects is real.

Certain supplements have indeed been shown to increase the risk of cancer among specific high-risk groups. The evidence that beta-carotene supplements cause lung cancer in current smokers is convincing, according to the AICR report.

(A judgment of convincing was the most exacting “grade” the AICR expert panel assigned to various links between diet and cancer; the next strongest links earned a grade of probable. Other grades included limited, but suggestive; limited, but no conclusion possible and finally substantial effect on risk unlikely.)

Of all the supplements reviewed by the panel, only two seemed to have a potential role in protection, and even then the research was less than clear. According to the panel, selenium probably protects against prostate cancer, while calcium probably protects against colorectal cancer. Yet they also concluded that high calcium consumption probably increases risk for prostate cancer.
Whole Foods vs. Supplements

The data on prevention are considerably more consistent, however, when it comes to foods that contain many of the same vitamins, minerals and other substances that are often sold in supplement form. The panel judged the evidence on several categories of such foods as protective against a variety of cancers, including:

* Foods containing folate are probably protective against pancreatic cancer
* Foods containing carotenoids are probably protective against cancers of the mouth, pharynx, larynx and lung.
* Foods containing beta-carotene are probably protective against esophageal cancer.
* Foods containing lycopene are probably protective against prostate cancer.
* Foods containing vitamin C are probably protective against esophageal cancer.
* Foods containing selenium are probably protective against prostate cancer.

The panel also concluded that other categories of plant foods – including non-starchy vegetables, allium vegetables (onions, leeks, etc.), garlic and fruits in general are probably protective against seven different kinds of cancer.

Exactly why this is so remains unclear – perhaps other substances in whole foods actually provide the cancer protection; perhaps the substances in question interact in unknown synergistic ways to reduce risk, or perhaps diets high in these foods simply tend to be lower in foods linked to increased risk, such as red and processed meat. But the bottom line remains: diets high in plant foods are associated with greater protection against many different kinds of cancer.

The AICR report collectively examined over 7,000 studies on all aspects of diet, physical activity, weight and cancer risk, Collins said. “When you compare the evidence on whole foods to the evidence on supplements, there’s simply no contest,” said AICR’s Collins. “It’s clear that choosing nutrient-rich whole foods and drinks is preferable to loading up on dietary supplements.”

The panel noted, however, that if low-dose dietary supplements are used to supplement (and not replace) healthy diets, they may offer some health benefits in other regards. Some examples include vitamin B12 (for people over 50 who have difficulty absorbing natural B12), folic acid (for women who may become or who are pregnant) and vitamin D (for people who are not exposed to sufficient sunlight or who do not synthesize adequate amounts from sunlight.) A doctor or nutritionist may make more specific recommendations in accordance with an individual’s nutritional needs.


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