People are firmly in charge of much of their own risk of cancer. The team at Harvard Medical School calculated that 20 to 40 percent of cancer cases, and half of cancer deaths, could be prevented if people quit smoking, avoided heavy drinking, kept a healthy weight, and got just a half hour a day of moderate exercise. They used data from long-term studies of about 140,000 health professionals who update researchers on their health every two years for the analysis, published in the Journal of the American Medical Association's JAMA Oncology. These figures increased to 40 percent to 70 percent when assessed with regard to the broader U.S. population of whites, which has a much worse lifestyle pattern than our cohorts," Dr. Mingyang Song and Dr. Edward Giovannucci of Harvard Medical School wrote. "The findings of the current study provide strong support for the argument that a large proportion of cancers are due to environmental factors and can be prevented by lifestyle modification." By "environmental," they mean non-genetic causes. To a scientist, environment includes diet, exercise and other factors. "Cancer is preventable," Dr. Graham Colditz and Dr. Siobhan Sutcliffe of Washington University School of Medicine ... agreed in a commentary. "In fact, most cancer is preventable - with estimates as high as 80 percent to 90 percent for smoking-related cancers ... and as high as 60 percent for other common, lifestyle-related cancers."