The average adult produces and removes 250,000 to 500,000 cancer cells every day. In most cases, the body routinely wipes out these cells before they have a chance to multiply. So why do some people still get cancer?

Aside from genetics—which is the cause of 10% of all malignancies—cancer and other inflammatory diseases largely depend on a particular “internal environment” to flourish. People who live a healthy lifestyle have an internal environment that helps prevent inflammatory diseases, such as heart disease, diabetes and rheumatoid arthritis, from progressing. Because inflammation is the underlying cause of many serious diseases, people who avoid and remove inflammatory substances are far less likely to get sick in the first place and more likely to recover when they do. How to clean up your internal environment…

DISEASE-FIGHTING MUSHROOMS

It’s only in the last decade that scientists have begun to understand the health benefits of Japanese mushrooms, particularly shiitake, enoki, maitake and reishi mushrooms. They have antiviral and antibacterial properties…increase immunity…and reduce the risk for heart disease and cancer.

In a Japanese study, women who ate about three and a half ounces of shiitake mushrooms daily reduced their cholesterol levels by up to 12%. The same mushrooms contain the anticancer compound lentinan, which is so potent that it’s been approved in Japan as a chemotherapeutic agent.

My advice: Eat shiitake mushrooms (and a variety of the other types described earlier) as often as possible.

ANTIOXIDANT POWER

The average person’s DNA experiences 10,000 daily oxidative “hits,” which can eventually lead to cancer and other chronic conditions. To reduce this threat, we must increase our levels of antioxidants (vitamins and other nutrients that remove potentially damaging oxidizing agents from our bodies). Best antioxidants…

Vitamin C. Vitamin C is a potent dietary antioxidant. For example, a study at the University of California, Berkeley, found that the oxidation of LDL “bad” cholesterol stopped when people had adequate vitamin C in the blood. This is critical because oxidized LDL is far more likely to accumulate on artery walls and lead to heart disease. Recommended dose: 500 mg, two to three times daily.

Beta-carotene and other carotenoids, such as lycopene and the “superantioxidant” astaxanthin, are on a par with vitamins C and E for reducing oxidation and inflammation. Bonus: Foods that are high in carotenoids are also high in other antioxidants.

You don’t need carotenoid supplements as long as you include grains, vegetables and/or beans in 19 of 21 meals a week. Good choices: Whole grains, prunes, blueberries, red beans, broccoli and pecans.

AVOID “NORMAL WEIGHT OBESITY”

Even if you’re just a few pounds overweight, your risk of getting cancer can be higher than it should be.

Reason: Fat is a metabolically active substance that increases oxidation and inflammation. It also elevates hormones that increase the risk for cancers of the breast and the prostate. Important: Many people who think they’re lean are heavier than they should be—a condition called “normal weight obesity.” My advice: You don’t need “six-pack” abs but should be able to see your abdominal muscles.

EXERCISE TO PREVENT CANCER

Everyone knows that exercise is good for the heart. What you might not realize is that regular exercise is among the best ways to prevent cancer.

When researchers at the renowned Cooper Clinic compared exercise with cancer rates, they found that men who didn’t exercise had four times more cancer than those who were fit. Sedentary women were found to have 16 times the cancer risk of fit women.

Reason: People who exercise have less inflammation throughout the body and a healthier balance of hormones. Their immune systems are more robust and are more likely to destroy cancer cells as well as viruses and bacteria.

Less is more: Interestingly, the Cooper study found that women who merely walked for 30 minutes a day, five days a week, significantly lowered their risk for breast cancer.

LAUGH IT UP

A Mayo Clinic study found that optimistic people lived almost 20% longer, on average, than pessimists. People who are upbeat and manage stress appropriately have lower blood pressure, are less likely to be overweight and suffer from fewer autoimmune diseases than those who are tense and angry.

Positive emotions are good medicine—they create a healthy, balanced internal environment without excess levels of damaging stress hormones, such as cortisol, which lead to inflammation.

But how do you relax in a stressful world or make yourself happy when you’re feeling down? Try this: Smile even when you don’t feel like it. Facial expressions don’t only reflect our feelings, they create them. When you smile, the movement of facial muscles causes blood to circumvent the cavernous sinus cavity, the area where blood is warmed before reaching the brain. Cooler blood in the brain triggers chemical changes that create pleasant feelings.

BREATHE CLEAN AIR

Polluted air—from industrial toxins, cigarette smoke, etc.—is a significant cause of disease. The oxidants in pollution, also known as free radicals, damage DNA and trigger inflammation throughout the body, including in and around the blood vessels. Important: Don’t smoke, and avoid secondhand smoke, too. Cigarette smoke contains more than one million oxidants in a single puff of smoke.

Helpful: Use an air purifier to clean indoor air, particularly if anyone in your household smokes. I recommend the Sun Pure Air Purifier SP-20 ($549), 800-469-7583, www.Natural-Living.com…and Aireox D-Model 45 ($360), 800-670-7480, www.Alerg.com.