Preventing Cancer

On December 23, 1971, President Richard M. Nixon signed the National Cancer Act, effectively declaring war on cancer. Thirty-nine years later, however, cancer remains the number-two cause of death, just behind cardiovascular disease. The statistics recently released by the American Cancer Society provide mute testimony that cancer is holding its own against the onslaught of research targeting it. While cancer death rates have dipped slightly during the past 15 years, the numbers of new cases of cancer are expected to rise. Here’s a sampling of the American Cancer Society’s statistics:

• In 2009 1,479,350 people were diagnosed with cancer.

• Cancer kills 562,340 annually.

• It kills 1,500 people every day.

• The most common cancers in men are prostate, lung and colon, with prostate cancer accounting for 25 percent of cases.

• In women the most common cancers are those affecting the breast, lungs and colon, with breast cancer alone accounting for 27 percent of cases.

• Perhaps most telling of all, one-third of cancer cases will result from obesity, lack of exercise and poor nutrition habits.

A common misconception is that cancer results largely from genetic defects. True, having an immediate relative with some form of cancer does increase risk, but only 5 to 10 percent of cancer arises from genetic defects. Lifestyle and environment account for 90 to 95 percent of most chronic illness, including cancer. That’s good news, though, because it means that cancer is a preventable disease. Indeed, a report published in 1981 found that 30 to 35 percent of cancer deaths in the United States were linked to poor diet. Emerging research shows that exercise also plays an important role in cancer prevention.

Probably the most interesting study connecting exercise to cancer was published earlier this year and sounded good to those of us engaged in regular bodybuilding activity.1 It tracked the lifestyles of 8,677 men, aged 20 to 82, for more than 20 years. Those who trained with weights and had the highest level of muscle strength were 30 to 40 percent less likely to die from cancer. The effect proved true even in subjects who had excess abdominal fat. The researchers strongly recommended that men lift weights at least twice weekly, training both upper- and lower-body muscles.

So it appears that the major way to prevent all types of cancer is through diet and exercise. The one exception to that rule is smoking. The major cause of lung cancer, smoking also increases the risk of at least 14 other types of cancer. In fact, 25 to 30 percent of all deaths from cancer result from smoking. No surprise there: Tobacco contains at least 50 known carcinogens, or cancer-causing substances. So the first rule in preventing cancer is to avoid all forms of tobacco—even cigars, Governor Schwarzenegger.

To understand how exercise and diet help prevent cancer, you need to understand a bit about how cancer forms.

What Is Cancer?

Simply put, cancer involves unruly cells that don’t follow normal replication patterns. Uncontrolled cell growth and tumor spread are its hallmarks. The process begins when a normal cell is converted into a precancerous cell, known as initiation. It can be caused by direct exposure to carcinogens, such as chemicals, radiation and even bacteria and viruses.

Frequent major players in the conversion of normal cells into cancer cells are free radicals, which are by-products of oxygen metabolism and have a strong tendency to attack cellular fatty membranes. When free-radical activity compromises the membranes, the cell door opens and makes way for DNA mutation. When that occurs, cancer begins.

Normally, the body can repair DNA effectively—for example, by deploying a nutrient like folic acid. If that kind of repair didn’t take place, we’d all rapidly succumb to cancer.

Another backup mechanism is your immune system. Certain immune cells, such as T cells, recognize incipient tumors and destroy them before they take hold. Interestingly enough, that same immune reaction can contribute to cancer later in life by promoting inflammation. That explains why older people have much higher rates of cancer: They have had long-term systemic inflammation, which fans the flames of tumors.

Having a cell initiated toward cancer doesn’t mean that you’ll get the disease. Something else must encourage the conversion of an initiated cell into actual cancer, a process known as promotion. The key to preventing cancer is to interfere with that process. That’s where exercise and diet enter the picture. Certain nutrients, collectively known as antioxidants, can neutralize dangerous free radicals before they can do their dirty work on cellular membranes. Such fat-soluble nutrients as vitamin E actually embed themselves in cell membranes, where they block free-radical attacks.

The Exercise Factor

In a study published last year in the British Journal of Cancer, researchers studied 40,708 men, aged 45 to 79, for seven years. During that time 3,714 men developed cancer, and 1,153 died from it. Those who walked or cycled for at least 30 minutes a day, however, had a 33 percent greater survival rate than the men who didn’t exercise. Those who exercised for 60 to 90 minutes daily had a 16 percent lower incidence of cancer. The effect of exercise is particularly strong in the case of prostate cancer. A 2005 study of 47,000 men followed for 15 years found that men over 65 who engaged in three hours of vigorous activity a week were 70 percent less likely to die from prostate cancer or be diagnosed with an advanced form of the disease. The same benefits weren’t found in younger men, in whom prostate cancer is relatively rare anyway.

In another study published by researchers from UCLA, the combination of a lowfat, high-fiber diet and exercise resulted in a 30 percent slower growth of prostate tumors. Black men have rates of prostate cancer about twice as high as white men, but a recent study offered good news: Black men who reported exercising regularly at least four hours a week between ages 19 and 29 were 35 percent less likely to develop prostate cancer. More than seven hours a week of exercise between ages 35 and 39 decreased the risk of prostate cancer by 41 percent.

What is it about exercise that helps prevent cancer? Some doctors think that by lowering testosterone, exercise may help prevent prostate cancer. That, however, assumes that testosterone causes prostate cancer, which is patently false. More likely, exercise helps prevent cancer by enhancing immune response, particularly that of T cells, which destroy tumors before they spread.

Exercise also aids the activity of the body’s built-in antioxidants, such as superoxide dismutase and glutathione. That heightened antioxidant defense helps protect vulnerable cell membranes against free-radical attack. That makes sense, since exercise involves a greater oxygen intake, which would result in greater free-radical production. The body responds by upgrading its internal antioxidant defense network.

Exercise also lowers bodyfat. That’s important for at least two reasons. One is that having excess bodyfat can increase the activity of hormones that can act as carcinogens, such as estrogen. In men, testosterone can be converted to estrogen by way of the enzyme aromatase, which is abundant in fat tissue. Excess estrogen has been implicated in causing prostate cancer in men, as well as breast cancer in women. Having excess bodyfat also increases the release of inflammatory chemicals from fat cells that produce low-grade systemic inflammation, the underlying cause of most forms of cancer.

How Bodyfat Is Related to Cancer

Far from being just a passive storehouse of excess calories, fat tissue is an active organ that secretes more than 100 different substances that are collectively known as adipokines. Because most of them are inflammatory, they can facilitate the cancer process.

In addition, most people with excess bodyfat are hyperinsulemic, meaning that they secrete too much insulin. The usual cause of that is insulin resistance, which in turn is related to increased fat stores in the liver and abdominal areas. Insulin can stimulate cell proliferation, the process by which cancer grows, in a number of ways. It can promote the release of insulinlike growth factor 1. While IGF-1 is considered an anabolic hormone, it also fosters the survival and spread of cancer cells.

The body controls IGF-1 by binding it to proteins produced in the liver. Insulin, however, frees IGF-1 from those proteins, enabling it to interact freely with cells, including cancer cells. Both insulin and IGF-1 increase the presence of leptin, an adipokine that is released by fat cells. Leptin is a key player in appetite and energy balance. On the downside, however, it induces the substance that permits angiogenesis, or the formation of new blood vessels. Tumor cells need angiogenesis to grow and spread. Leptin is linked to higher insulin counts in the obese, as well as to higher rates of colon and prostate cancers. Leptin is also a culprit in overall inflammation, helping release such inflammatory mediators as interleukin-6.

In short, having excess bodyfat fosters the systemic inflammation that helps cancer spread. Exercise lowers bodyfat and may help counter the effects of inflammatory fat cell chemicals.

The Role of Nutrition Against Cancer

The first nutritional tactic for helping prevent cancer is simply not to overeat. Taking in too many calories is known to fuel cancer growth. One mechanism is the release of excess free, or unbound, IGF-1. While essential for the preservation of both nerve and heart cells, IGF-1, in the context of overeating, prevents the self-destruction of tumor cells. Overeating also leads to obesity and, in due course, increased systemic inflammation, the cornerstone of cancer.

Further evidence of the effect of calorie reduction is seen in animal studies, in which animals with restricted daily calorie intake (not nutrient intake) show far fewer tumors than animals that overeat. The effect is thought to be due to less release of systemic IGF-1.

Fruits and vegetables have proven to provide the most beneficial effects against cancer. They contain more than 25,000 different substances collectively known as phytochemicals, many of which exert potent anticancer activity. Some contain nutrients such as folic acid, which stabilizes and helps repair damaged cellular DNA.

Studies show that people who eat few or no daily servings of fruits and vegetables have about twice the risk of acquiring cancer. Some fruits and vegetables have better anticancer properties than others. For example, alliums, such as garlic and onions, are very protective against stomach and colorectal cancers. Cruciferous vegetables, such as broccoli, brussels sprouts, cauliflower and cabbage, are true anticancer powerhouses. They contain compounds that boost antioxidant activity and spur the activity of liver enzymes that make war on carcinogens in your diet. One study found that eating three servings a week of cruciferous vegetables resulted in a 41 percent decrease in the risk of prostate cancer.

Cruciferous veggies also convert the active form of estrogen, an established carcinogen, into biologically inert forms that don’t cause cancer. They protect against all estrogen-sensitive cancers, including breast, uterus and prostate cancers.

Lycopene is a carotenoid found in tomatoes and other foods. It’s more absorbable cooked rather than raw. The prostate gland concentrates lycopene more than any other organ in the body. In the prostate, lycopene is thought to prevent the oxidation that leads to cell mutations and cancer. It also appears to block IGF-1 from helping to form tumors in the prostate. Studies have shown that lycopene provides a 35 to 53 percent protective effect against prostate cancer.

Green tea protects against cancer in a number of ways, most involving potent antioxidant activity. I covered precisely how green tea operates in a recent IRON MAN feature [February and March ’08].

Fish oil may protect against cancer by modulating the inflammatory cascade associated with the metabolism of arachidonic acid, an omega-6 fatty acid. A growing body of research indicates that an imbalanced ratio of omega-6, or vegetable oils, to omega-3 fats results in excess inflammation in the body. Omega-9 fats, such as that found in olive oil, have neutral effects on inflammation.

Bodybuilders generally revile soy because they think it lowers testosterone. Well, that’s simply not true. What is true is that soy contains isoflavones that provide antioxidant activity and also act as phytoestrogens. Soy isoflavones do interact with one type of estrogen receptor, estrogen-b, which blunts the effects of the type of estrogen receptor that is linked with cancer, known as estrogen-a. Soy intake is associated with lower rates of breast, endometrial and prostate cancers.

While a complete discussion of specific nutrients that provide cancer protection is beyond the scope of this article, special mention should be made of vitamin D, which appears to boost immune response. That helps the body ward off incipient tumor development. Most people are borderline deficient in vitamin D, so taking a supplement of at least 2,000 units daily would help boost immune response and offer protective effects against cancer. Selenium also deserves mention; one study showed that it offered about 40 percent decreased risk of prostate and other cancers. Here again, the mechanism is primarily antioxidant activity.

Many studies suggest that eating too much red meat may lead to cancer. On the other hand, when you look at the suggested mechanisms for this effect, the “danger” of eating red meat is less apparent. The studies suggest that overcooked or well-done meat contains carcinogens. You can easily avoid that by not overcooking meat. The other mechanism is that meat contains heme iron, which is reactive and can result in a higher free-radical release. Again, the solution is simple: Ensure an adequate intake—nine to 11 servings daily—of fruits and vegetables, which will provide the antioxidant activity to neutralize heme iron. Green tea also blocks that effect, as does grapeseed extract. There is no need to avoid eating red meat. What should be avoided is processed meats, such as sausages and hot dogs, which are linked to stomach cancer.

The effect of fiber intake is controversial in relation to prevention of colorectal cancer. Some studies show no effect, and others show a potent protective effect. The mechanism, however, is plausible, so it makes sense to take in at least 40 to 60 grams of fiber a day to protect against various gastrointestinal cancers.

Following the guidelines discussed in this article will likely help prevent you from becoming a casualty in the war against cancer.

1 Ruiz, J.R., et al. (2009). Muscular strength and adiposity as predictors of adulthood cancer mortality in men. Cancer Epidemiol Biomarkers Prev. 18:1468-76. IM