Lifestyle Risk Factors for Prostate Cancer
A great deal of effort has been devoted to searching for lifestyle or environmental factors that might serve as promoters for prostate cancer. The incidence of microscopic prostate cancer (cancers too small to be seen except under a microscope) is similar among men in the United States and in all other countries that have been examined. However, the death rates from prostate cancer differ from one country to another and even within different regions of the United States.
These differences suggest that factors such as diet, exercise, body weight, or exposure to certain substances or forces influence prostate cancer's progression from microscopic tumors to clinically significant ones.
Some factors are believed to encourage the growth of prostate cancer, whereas others may have a protective effect. It is important to remember, however, that the effects of diet and lifestyle are difficult to study and that research results are often conflicting. Some researchers believe that an individual's overall dietary patternfollowing a primarily plant-based diet, for instancemay be more important than individual foods and nutrients.
Dietary Fat and Prostate Cancer Risk
Many studies that have looked at the relationship between dietary fat and prostate cancer have found a higher risk of the disease among men with a higher fat intake (especially saturated fat from animal products). Fat makes up 30 to 40 percent of the calories in the American diet, compared with 15 percent in Japan. This difference in fat consumption may help explain the much lower death rate from prostate cancer in Japan as well as the great variability in prostate cancer mortality rates around the world.
It is also possible that people who consume large amounts of high-fat foods are less likely to eat healthful foods, like fruits and vegetables, which may protect against cancer. Omega-3 fatty acids, which have anti-inflammatory and anti-cancer effects, are an important exception. These "good fats" are abundant in fatty fish like salmon, sardines, tuna, and halibut and in fish oil. Several studies suggest that men who eat fish two or more times per week have a reduced risk of developing prostate cancer. Flaxseed, walnuts, and canola oil contain a weaker but still beneficial form of these healthy fats.
Vegetables, Fruits and Soy and Prostate Cancer Risk
A high intake of vegetables may lower the risk of prostate cancer. In a study in the Journal of the National Cancer Institute, men who ate 28 or more servings of vegetables a week were 35 percent less likely to develop prostate cancer than those who ate 14 or fewer servings per week.
Men who ate cruciferous vegetables, such as cabbage and broccoli, appeared to be at even lower risk: Those who ate three or more servings of cruciferous vegetables a week (in addition to other vegetables) had a 41 percent lower risk of prostate cancer than those who ate less than one serving a week. Cruciferous vegetables are rich in substances that help detoxify cancer-causing substances (carcinogens).
Regular consumption of soy foods (such as tofu, soy protein, and soymilk) has been linked to a reduced risk of developing prostate cancer. Lycopene-rich cooked tomato products (for example, tomato paste, spaghetti sauce, and ketchup) also may be protective. (Lycopene is an antioxidant, a substance that detoxifies damaging molecules called free radicals.) For example, in the Physicians' Health Study, men who consumed the most tomato products had a lower risk of prostate cancer than those who consumed the least.
In addition, pomegranates and pomegranate juice (which have strong anti-inflammatory and antioxidant effects) are under investigation for their potential to slow the progression of prostate cancer.
Vitamins and Minerals and Prostate Cancer Risk
Both vitamin E and the mineral selenium have long been under study for their potential to prevent or slow the progression of prostate cancer. In one early study, men who took vitamin E supplements had a 34 percent reduction in the incidence of prostate cancer.
Another study found that men who took selenium supplements had a two-thirds reduction in the risk of developing prostate cancer. But in late 2008, long-awaited results from a large, nationwide clinical trial called SELECT (Selenium and Vitamin E for the Prevention of Prostate Cancer) found that men who took vitamin E, selenium, or both developed prostate cancer as often as men who did not take them.
In recent years, a high intake of calcium has come under scrutiny as a possible risk factor for prostate cancer. In one study, the risk of developing advanced prostate cancer was 2.5 times higher among men who consumed 2,000 mg or more of calcium per day than among men with a daily consumption of 500 to 749 mg. For now, a sensible approach is to limit calcium consumption to no more than 1,200 mg per day through food sources.
Energy Balance and Prostate Cancer Risk
The relationship between calories taken in versus calories burnedenergy balancealso may affect prostate cancer risk. Animal research has shown that implanted cancers grow more slowly when the animals' calorie intake is restricted. Preliminary evidence suggests that men with the greatest calorie intake are more likely to develop prostate cancer than are those whose consumption is more modest.
In one study, men who consumed the most calories (approximately 2,600 per day) were nearly four times as likely to have prostate cancer as men who consumed the least (1,100 per day). Nonetheless, more research is needed before recommendations regarding calorie intake can be made.
Regular vigorous physical activity helps improve energy balance by burning calories, and increasing research suggests that exercise offers a protective effect against prostate cancer. Results from the Health Professionals Follow-up Study indicate that men age 65 or older who are vigorous exercisers are 70 percent less likely to develop life-threatening prostate cancer.
Excess Weight and Prostate Cancer Risk
Obesitydefined as having a body mass index (BMI) of 30 or moreis known to increase the risk of some types of cancer as well as cancer deaths. It is unclear whether obesity influences the development of prostate cancer specifically; however, several studies have found that obese men have higher-grade prostate cancers at diagnosis and a higher risk of cancer recurrence after radical prostatectomy and radiation treatment than men who are not obese. Researchers hypothesize that obesity may contribute to cancer progression by altering blood levels of sex hormones or insulin.
Sunlight Exposure and Vitamin D and Prostate Cancer Risk
Sunlight may protect against prostate cancer by promoting the body's production of vitamin D. Vitamin D is produced in the skin during exposure to the ultraviolet (UV) radiation in sunlight.