4 Risk Factors for Prostate Cancer
Autopsy studies have shown microscopic evidence of prostate cancer in 15 to 30 percent of men over the age of 50 and in 60 to 70 percent of men who reached age 80. These numbers have led some experts to theorize that every man will develop some degree of prostate cancer if he lives long enough.
Although the number of men diagnosed with prostate cancer increased with the widespread use of the prostate-specific antigen (PSA) blood test for screening, prostate cancer death rates began to decline after 1993 and have continued to fall. Many experts believe that earlier detection of prostate cancer through routine use of the PSA test was responsible for at least half to three quarters of the decline in death rates. Nevertheless, prostate cancer screening has been a matter of great debate.
A boy born today has a 16 percent chance of being diagnosed with prostate cancer at some time in his life and an approximately 2 to 3 percent chance of dying of the disease. The good news is that the vast majority of men diagnosed with prostate cancer will live as long as men in the same age group who never develop the disease.
What puts you at risk
The underlying cause of prostate cancer is unknown. As with other cancers, however, multiple events over a period of many years are probably necessary to produce a cancerous change in a prostate cell. The development of cancer is broadly viewed as a two-step process. In the first step, cancer is initiated through genetic alterations in the cell. This is followed by cancer promotion, a process that allows the cancerous cells to continue to grow and progress. The study of factors that initiate and promote prostate cancer is an active area of investigation.
Age, race and family history are important risk factors. Diet and lifestyle factors also may influence whether a man will develop the disease. Generally, studies have not shown a clear link between the development of prostate cancer and regular alcohol intake, smoking, vasectomy or the presence of benign prostatic enlargement, or BPE.
Increasing evidence suggests that fat intake, physical inactivity or being overweight may influence the development or progression of prostate cancer, especially the more aggressive form of the disease. Whether testosterone replacement therapy affects the development or progression of prostate cancer is not clear. If prostate cancer is present, however, it could cause the disease to progress more rapidly in some men.
Here’s what puts you at risk:
1. Age. As a man ages, his risk of developing prostate cancer increases dramatically. This age-related increase is greater for prostate cancer than for any other type of cancer. The average age at diagnosis is between 65 and 70 years; the average age at death between 80 and 85 years.
2. Race. The incidence (new cases per year) of prostate cancer in the United States varies by race. Black men are at highest risk; whereas the rates for white men and Hispanic men are 40 to 50 percent lower. Asian/Pacific Islander and American Indian men have the lowest rates.
3. Family history. Studies of identical and fraternal twins have found that prostate cancer has a stronger hereditary component than many other cancers, including breast and colon cancer. Having one first-degree relative (a brother or father) with prostate cancer doubles the risk of developing the disease; having a second-degree relative (an uncle or grandfather) with the disease confers only a small increase in risk.
A number of genetic alterations that affect how the body handles inflammation and infections, fat metabolism, repair of genetic damage and other processes have been linked to prostate cancer development and progression. For example, researchers have discovered that gene fusions—a process in which genes separate from their normal location and fuse to another gene—are an early event in prostate cancer development.
Researchers at Johns Hopkins University found that men who inherit a rare mutation on a gene known as HOXB13 are up to 20 times more likely than noncarriers to develop prostate cancer. However, the mutation is responsible for only 2 to 5 percent of prostate cancer cases. In most cases, rather than inheriting a defect in a single gene that results in prostate cancer, it is more likely that minor variations in a number of genes (any one of which alone may have no adverse effects) when combined may act like the “perfect storm” to increase a man’s risk. The lifestyle choices a man makes during life most likely act in concert with these genetic variants to cause the development and progression of prostate cancer. Although genes can influence a man’s risk of developing prostate cancer, other factors also are at work. The likelihood that identical twins (who share all genetic information) will both develop prostate cancer is 27 percent. This suggests that lifestyle choices can modify the effects of the genetic cards that a person is dealt at birth.
4. Lifestyle factors. Much 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. But 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.
Effects of diet and lifestyle
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 pattern—following a primarily plant-based diet, for instance—may be more important than individual foods and nutrients. Here are some factors to consider:
• Dietary fat. 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 typical 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, such as fruits and vegetables, which may protect against cancer.
Omega-3 fatty acids, which have anti-inflammatory and anticancer effects, are an important exception. These “good fats” are abundant in fatty fish like salmon, sardines, tuna and halibut and in fish oil. Some studies suggest that men who eat more fish 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 and fruits. 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 four or more servings of vegetables a day were 35 percent less likely to develop prostate cancer than those who ate two or fewer servings per day. 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 soy milk) 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, although this is controversial. (Lycopene is an antioxidant, a substance that detoxifies damaging molecules called free radicals.) In the Physicians’ Health Study, men who consumed the greatest amount of tomato products had a lower risk of prostate cancer than those who consumed the least.
• Vitamins and minerals. Both vitamin E and the mineral selenium have been evaluated for their potential to prevent or slow the progression of prostate cancer. Early studies that were not controlled suggested that men who took vitamin E supplements and selenium supplements had a reduction in the risk of developing prostate cancer. These studies prompted a large randomized trial called SELECT (Selenium and Vitamin E Cancer Prevention Trial). Findings from SELECT demonstrated an increased risk of prostate cancer among vitamin E users. In recent years, a high intake of calcium has come under scrutiny as a possible risk factor for prostate cancer, especially for men consuming 2,000 mg or more of calcium each day. For now, a sensible approach is to limit calcium consumption to no more than 1,200 mg per day through food sources.
• Energy balance. The relationship between calories taken in versus calories burned—energy balance—also 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. Obesity—defined as having a body mass index (BMI) of 30 or more—is 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. Some researchers hypothesize that obesity may contribute to cancer progression by promoting inflammation and altering blood levels of hormones that enhance cancer growth.
• Sunlight exposure and vitamin D. 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.