By William J. Cromie

Gazette Staff

Preventing cancer depends on lifestyle changes as much as it does on further research and government regulations, according to a new report from the School of Public Health.

Almost 7 in 10 cancer deaths in the U.S. are linked to tobacco use, diet, excess weight, and lack of exercise, according to the Harvard Report on Cancer Prevention, published this week.

"By addressing these risk factors, we believe that cancer mortality in this country can be reduced by one third to a half," says Dimitrios Trichopoulos, one of the report's authors and director of the Harvard Center for Cancer Prevention. "You can't reach the ideal of preventing all cancer deaths due to lifestyle because some people just won't stop smoking and eating red meat, or start exercising daily," he notes.

The summary of virtually all cancer studies to date concludes that 30 percent of cancer mortality comes from smoking and other uses of tobacco, 30 percent from excess weight and eating too much fat and not enough fruit and vegetables, and 5 percent from

lack of exercise.

Concern about cancer-causing chemicals, pollutants, radon gas, and electric power lines "is out of proportion with the true risk," according to the report. Environmental pollutants account for 2 percent of cancer deaths, the same proportion as too much sunbathing and less than excessive alcohol use (3 percent).

No proof exists that electric power lines and appliances cause cancer, or for claims that indoor radon gas causes 10 percent of lung cancer deaths.

Exposure to cancer-causing substances in the workplace, family history of cancer, and viruses each raises the fatality risk by 5 percent.

"Many people believe that genes are involved in most cancer deaths," notes David Hunter, associate professor of epidemiology and an author of the report. "However, only 5 percent of the risk comes from inherited genes, the rest comes from mutations accumulated during a person's lifetime." Such mutations come from smoking, animal fat, and other demons mentioned in the report.

Body size is also a 5 percent factor. Taller people get more cancer. The researchers blame this on eating many more calories than necessary and failing to burn them off with activity.

"Excess energy intake in life is probably responsible for the positive association between height and risk of breast and possibly other cancers," Hunter says. Evidence is also emerging that larger birth weight raises the risk of breast and, perhaps, prostate cancer.

Early age at menarche, late age at first birth, and late menopause also raise the risk of breast cancer, accounting for an estimated 3 percent of cancer mortality.

The authors link poverty with 2 percent of deaths, particularly from lung, stomach, and uterine cancers. Being at the bottom of the socioeconomic ladder is also associated with increased exposure to tobacco smoke, alcoholism, poor nutrition, and increased infections.

Smoking and Eating Dangers

With monotonous regularity, health experts keep reminding us that smoking causes lung cancer. "Stemming the epidemic of tobacco smoking is our most effective means for preventing cancer," the report insists.

This is true whether it's you or someone else smoking. "The involuntary exposure of nonsmokers to smoke from other people's tobacco products poses a health risk, including increased risks of lung cancer," says the report. It points out that tobacco smoke is a cancer-causing substance "for which there is no known safe level of exposure."

The report repeats the often heard recommendations for diet, albeit with a new urgency. Eat more fruits and vegetables; good evidence exists that this reduces risk of cancers of the lung, stomach, esophagus, and larynx. Evidence also exists that a diet high in legumes (the pea family), bread, pasta, and cereals decreases risk of stomach and pancreatic cancers.

As usual, the report repeats warnings about eating too much red meat (implicated in colorectal cancer), animal fat (linked to prostate cancer), refined carbohydrates, and salt.

Substituting plant oils, such as olive oils, for butter, margarine, and other fatty items, is suggested.

The final recommendation is to reduce calorie consumption in early life, avoid obesity in adult life, and increase activity throughout life.

The full report appears in the latest issue of Cancer Causes and Control. Besides Trichopoulos and Hunter, others who compiled the report include Graham Colditz, William DeJong, and Walter Willett, all members of the faculty of the School of Public Health.