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Prostate Cancer: the Diet Angle

After lung cancer, prostate cancer is the biggest cancer killer. No one knows what causes it, but like breast cancer, prostate cancer is influenced by sex hormones, and risk increases with age. Almost all men develop silentor latent prostate cancer cells if they live long enough. The big question is why a small percentage of them develop the kind of prostate cancer that kills.

The highest rates of prostate cancer occur in northern Europe and North America. The lowest rates are found in Asia. But when, for example, men move from Japan, where rates are low, to Canada or the U.S., their risk eventually goes up. Thus, many researchers think diet is one culprit. Other cultural, as well as genetic factors, are undoubtedly involved, too. African American men have the highest rate of prostate cancer in the world; Native Americans, Mexican Americans, and Chinese Americans have lower rates than other Americans. However, age remains the major risk factor.

Nothing is certain yet, but scientists have been looking at the following possible preventers and promoters of prostate cancer.

Possible protectors

A diet rich in fruits, vegetables, and whole grains. For one thing, a plant-based diet tends to be low in fat (see below). Moreover, plant foods are rich in vitamins, minerals, and various phytochemicals that may be beneficial. Many studies suggest that tomatoes are protective, possibly because they are rich in the carotenoid lycopene; cooked and processed tomatoes have more absorbable lycopene than raw ones. And cruciferous vegetables such as broccoli, kale, and cabbage contain compounds called indoles, which may inhibit the growth of prostate cancer cells. Still, it’s not clear which substances are most important, so it’s best to vary your intake of fruits and vegetables.

Selenium. Two major studies found that a high intake of selenium (200 micrograms daily) substantially lowered the risk of prostate cancer. But overall the evidence has been mixed, and there are many questions (see Wellness Letter, November 2005). Important research on selenium is underway. Too much selenium can be harmful, so get it from food—such as fish, whole grains, and Brazil nuts—and possibly from a multivitamin/mineral pill. If you take a selenium supplement, don’t take more than 200 micrograms a day.

Fatty fish. A 2001 Swedish study found that men who ate little or no fish were more than twice as likely to develop prostate cancer as those who ate moderate to high amounts. In a 2003 Harvard study, men who ate the most fish were least likely to develop advanced prostate cancer (fish oil supplements did not decrease the risk). Prostate cancer is very rare among Inuit men in Greenland, and researchers attribute this in large part to their high fish intake. Besides its healthful fats, fish is also a good source of vitamin D, which may be protective.

Vitamin D. People who get little or no sun exposure tend to have higher rates of prostate cancer, and mortality rates for this cancer tend to be higher in northern regions, where there’s less sun. Many researchers believe that lack of vitamin D may be the explanation, since the skin makes this vitamin when exposed to sunlight. Similarly, dark-skinned people may be at higher risk for prostate cancer because their skin makes less D. Fortified milk is the major dietary source; many people over 60 should take a supplement containing D (see Wellness Letter, October 2005).

Vitamin E. The evidence is weak. Though some early studies suggested a protective effect, more recent research has not. One large study found a benefit only in smokers.

Soy (primarily because of its isoflavones) and green tea are also under investigation. These are staples in most Asian diets, though no one knows if they are partly responsible for the lower rates of prostate cancer in Asia.

Possible bad guys

Dietary fat. This has been linked to increased prostate cancer risk since the 1970s, though not in all studies. If fat does play a role, it’s unclear whether the amount, type, or source is the key. Some studies point to red meat, and specifically to its saturated fat. But the problem could also be the carcinogens formed when meat is grilled. Or it could be that people who eat lots of meat tend to eat less produce.

Zinc. The findings about zinc have been contradictory. But in 2003 a study at the National Cancer Institute found that men who took more than 100 milligrams of zinc a day from supplements were twice as likely to develop advanced prostate cancer as those who took no zinc. Zinc increases blood levels of testosterone, which may promote prostate cancer. This is one reason to avoid high doses of zinc.

Calcium or dairy products. Some studies, including the Physicians’ Health Study, have linked high intakes of calcium and/or dairy to increased risk. But a few have found no connection, and some studies have even found a reduced risk. One complication: dairy products contain many nutrients besides calcium, some of which may decrease the risk of prostate cancer (such as vitamin D) or increase it (such as saturated fat). Don’t stop consuming dairy products for fear of cancer. For one thing, there’s fairly good evidence that dairy products may reduce the risk of colon cancer and hypertension, among other benefits.

Flaxseeds. Some doctors warn men to avoid flaxseeds because of worries about prostate cancer, but there actually has been very little research on this. One study found that flaxseeds seemed to increase tumor growth. But another showed that men with prostate cancer who ate flaxseeds daily were able to slow the growth of their cancer. There have been more studies on alpha-linolenic acid (ALA), a heart-healthy fat found in flaxseeds, but they, too, have yielded conflicting results. Flaxseeds also contain compounds called lignans, which may have an anti-cancer effect. Flaxseeds can be part of a healthy diet, but don’t go overboard. For the potential heart benefits, you need only a little ALA—the amount in less than 1 tablespoon of ground flaxseed, 1 tablespoon of canola oil, or half an ounce of walnuts a day.

Besides diet

Smoking and alcohol do not seem to affect the risk of prostate cancer. Vasectomy, despite some scary media reports a while back, does not increase the risk, nor does an enlarged prostate (benign prostatic hyperplasia). There’s some evidence that obesity increases the chances of developing aggressive prostate cancer or having it recur. Exercise may well reduce the risk, though researchers have had a hard time proving this. (An upcoming article will discuss exercise and various types of cancer.)

You may have heard that your sex life—that is, having too few, or too many, orgasms—affects the risk of prostate cancer. Studies on this have yielded contradictory findings. Don’t worry that your sex life is harming your prostate.

Reference Source 98
January 2, 2006

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