Obesity and Prostate Cancer
Men’s Health Series – Part 4
America is the land of plenty. The abundant supply of high-calorie foods and the labor-saving devices that enable sedentary living are the twin engines driving our obesity epidemic. At present, 30% of Americans are overweight, 30% are obese, and 5% are very obese. And the prevalence of obesity has increased steadily since the 1960s — and the nation’s waistline continues to grow.
The best information comes from a major study sponsored by the American Cancer Society. Beginning in 1982, scientists monitored more than 900,000 Americans. Over a 16-year period, more than 57,000 of them died from cancer. The risk of dying from cancer was 52% higher in obese men than in men of normal weight, and was 62% higher in obese women than in women of normal weight. All in all, the researchers estimated that obesity accounts for 14% of all the cancer deaths in American men and for 20% of the cancer deaths in women.
Obesity and the risk of prostate cancer
In the American Cancer Society study, obesity increased the risk of future prostate cancer. For men who were overweight, the extra risk was just 8%, but obesity increased a man’s risk by 20%, and severe obesity boosted it by 34%.
Studies from around the world agree with the American research. Scientists in Australia reported that obese men were 2.2 times more likely to develop aggressive prostate cancer than lean men were; each 22 pounds of excess weight boosted risk by 40%. Although Asian men tend to be admirably lean, abdominal obesity has been linked to a nearly threefold increase in the risk of clinical prostate cancer in China. In Italy, obesity at age 30 was implicated as a risk factor; in France, mere overweight did not affect risk, but obesity boosted the odds of prostate cancer by 2.5 times. Studies of men in California, Cleveland, and Detroit reported similar results, but several American studies suggest that obesity in youth may be somewhat protective.
Obesity and the results of treatment
Seven studies published between 2004 and 2006 examined the risk of surgical failure in men undergoing radical prostatectomies. In general, obese men were more likely to have unfavorable findings at the time of surgery; their tumors had higher Gleason scores (they looked more aggressive) and were more likely to extend through the gland’s capsule (so complete removal was more difficult). Even more important, in six of the seven studies, the obese men were more likely to experience recurrent or relapsing disease as indicated by rising PSAs following surgery. The greater the excess body fat, the worse the prognosis. One study of 873 men who underwent radiation therapy for prostate cancer linked obesity to an increased risk of recurrent disease, but another did not.
Technical difficulties facing the surgeon might help explain why obese men don’t fare as well as lean patients. Another explanation is that men who are obese may not seek medical care as promptly as lean men, so they may be diagnosed at a later state of the disease. Since PSAs tend to be lower in obese men than in lean gents, delayed diagnosis may also have a biological basis. But while technical difficulties and delayed diagnosis may play a role, they are not likely to be the whole story. Obese patients with kidney and bladder cancer pose technical challenges to surgeons, yet they respond to surgery as well as patients of normal weight.
Obesity is caused by a caloric imbalance: too many calories in the diet compared to the calories burned up by exercise. A 2003 study from Baltimore reported that men with the highest caloric intakes were nearly four times more likely to develop prostate cancer than those who consumed the fewest calories. And although the evidence is not conclusive, some research indicates that men who are physically active have a lower risk of prostate cancer than sedentary men. Obesity also alters the metabolism of sex hormones, which could affect the growth of prostate cancer. Most important, perhaps, obesity increases the level of growth factors such as insulin and insulin-like growth factor 1 (IGF-1). Both increase the rate of cell multiplication, and high blood levels of IGF-1 have been linked to an increased risk of prostate cancer as well as colon cancer and other malignancies.
The skinny on prostate cancer
A growing body of evidence links obesity to an increased risk of prostate cancer and, especially, to a poorer outcome for men with the disease. Staying lean will not provide immunity from prostate cancer, but it should help. And a lifestyle that includes a good diet and appropriate exercise will also go a long way to reducing the risk of heart attack, stroke, high blood pressure, and diabetes — as well as obesity and its malignant consequences.
Next in the series: Selenium and prostate cancer.
-- Harvard Health Publications – Harvard Medical School