Harvard Health Letters

Harvard Health Letters

About 12 million Americans are cancer survivors, and the number is almost certainly going to increase because of early detection, better treatment, and an aging population. After the first encounter with the disease and the ordeal of treatment, attention swivels to what can be done to prevent a second one.

As many as a third of cancer survivors start taking vitamin and mineral supplements. But should they? The American Cancer Society recommends staying away from high-dose supplements and sticking to the standard multivitamin just to fill in the nutritional gaps left by less-than-perfect diets. Other cancer organizations are similarly cautious.

Two Harvard researchers, Edward Giovannucci and Andrew T. Chan, reviewed the evidence on vitamin and mineral supplements for cancer survivors in an article published in the Journal of Clinical Oncology in 2010. Perhaps the most surprising thing they had to say is that studies of cancer survivors taking vitamins and minerals after their diagnosis haven't been done, so direct evidence is "essentially nonexistent."

Until that research is done, we must go by the results of studies of long-term supplement use and how it correlates with advanced or fatal cases of cancer. Those findings can't separate out the pre- and post-diagnosis effects of supplements, but as the Harvard researchers noted, data suggesting an increase in mortality or cancer progression for a specific supplement would, at the very least, warrant caution.

VITAMIN D IS A CONTENDER

The most encouraging news out of Giovannucci and Chan's review is that vitamin D is a prospect for lowering cancer recurrence. Vitamin D is generated in skin exposed to the ultraviolet B (UVB) part of the light spectrum, and people in higher latitudes with less exposure to UVB light from the sun have higher rates of fatal colon, breast, and ovarian cancer.

Moreover, the association is stronger for mortality than incidence, suggesting that vitamin D might have effects late in the disease process. Several threads of experimental evidence point to vitamin D having anticancer activity, and some animal experiments suggest particularly strong effects on metastasis -- cancer's spread from one part of the body to another.

Studies of lung, breast, and colon cancer patients help make the case for D: High levels of the vitamin in the blood of the patients in those studies were associated with lower rates of death and cancer coming back.

The research done so far doesn't prove that vitamin D supplements will reduce colon cancer recurrence. And vitamins have disappointed so many times now that enthusiasm must be tempered. Still, as the Harvard researchers note, there's enough evidence to merit further investigation with some well-designed clinical trials.

NOT SO PROMISING

The glass looks to be half empty -- or even worse -- for other vitamins. The antioxidant vitamins -- vitamin C, vitamin E -- don't seem to have broad anticancer effects, and beta carotene, a form of vitamin A, seems to increase the risk of lung cancer in smokers. Giovannucci and Chan hold out some flickering hope for vitamin E perhaps reducing the risk of advanced or fatal prostate cancer in smokers.

Folate may have a split personality, reducing the risk of precancerous colon polyps, but once they have developed, raising the risk of the polyps becoming full-fledged colon cancer. The Harvard researchers say it would be "prudent" for cancer survivors to avoid excessive folate intake.

That advice may be at odds with the American Cancer Society's endorsement of multivitamins, many of which contain 100 percent of the daily requirement for folate. The combination of folate from a multivitamin and from flour and cereal grains, which are fortified with folic acid (the synthetic form of folate), could add up to too much of the vitamin.

ASPIRIN: A DEFINITE MAYBE

In contrast to the wavering enthusiasm for vitamins, with the notable exception of D, things are looking up for aspirin, according to Giovannucci and Chan. They describe the evidence for aspirin reducing the risk of colon cancer recurrence as "compelling" and point to results from a randomized trial that showed a daily 325-mg dose of aspirin reduced the recurrence by 35 percent among about 500 patients who had been treated for early-stage colon cancer.

Another feather in the aspirin cap: Results in 2009 from a study led by Chan that linked a regular aspirin habit after a colon cancer diagnosis to a lowering of risk for dying from the disease.

Other types of cancer seem susceptible to aspirin's influence, too. A different group of Harvard researchers reported results in 2010 suggestive of protection against breast cancer recurrence. Results for lung cancer haven't been quite as encouraging.

So how is it that aspirin, the humble pain reliever, might keep cancer at bay? Aspirin inhibits the COX-2 enzyme. In addition to catalyzing inflammatory processes that are part of pain, COX-2 is involved in others that influence cell growth and therefore the development of cancer. By blocking COX-2, aspirin may have the ability to steer wayward cells away from a cancerous fate and, if the current findings hold up, maybe it can do the same for some cancer survivors.

Giovannucci and Chan envision a day when cancers might be tested for their COX-2 status so doctors and patients would know if taking an aspirin is worth it. -- Harvard Health Letter

 

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Last Child in the Woods: Saving Our Children From Nature-Deficit Disorder

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Nutrition at Your Fingertips

 

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