You’ve heard that skyrocketing obesity is increasing our risk of heart disease and diabetes. A new study of more than 900,000 American adults reports that cancer is also related to excess weight. After following people for 16 years, researchers estimate that current patterns of overweight and obesity in the U.S. could account for 14 percent of all cancer deaths in men and 20 percent of those in women.
This research, reported in the New England Journal of Medicine, demonstrates that as our weight increases beyond a healthy range, so does our risk of many types of cancer. Looking at the overall risk of cancer death, the lowest level of obesity raises risk nine percent in men and 23 percent in women. More severe obesity raises that risk much higher: 20 to 52 percent in men and 32 to 62 percent in women. Overweight and obesity are most strongly related to risk of death from cancers of the colon, liver, gallbladder, pancreas, kidney, prostate, breast, uterus, cervix and ovaries.
The links between overweight and overall risk of cancer, as well as the identification of specific cancers that are weight-related, have been reported in previous research. A Swedish study published in the journal Cancer Causes and Control found about 33 percent greater cancer incidence among the obese than among those of normal weight. A few years earlier, a landmark report on diet and cancer risk by the American Institute for Cancer Research (AICR) attributed certain cancers to obesity: 15 to 30 percent of uterine cancer deaths, 11 to 30 percent of breast cancer cases and 25 to 33 percent of kidney cancer occurrence.
In comparing these results with those of other reports, we need to note that the statistics in the most recent study refer to death rates from various cancers. That means we are seeing the total effect of weight on the development of various cancers, as well as any impact on survival and even diagnosis. Both the AICR report and a new report on cancer from the World Health Organization (WHO) agree that the international epidemic of obesity is a major part of today’s cancer risk. Both reports identify cancers of the colon, kidney, uterus and breast (after menopause) as obesity-related, and WHO adds esophageal cancer to the list. In the most recent study, researchers adjusted statistics to account for the influence of various factors on colon cancer, including fat and vegetable consumption as well as physical activity. Interpreting the results, they say that, with all three factors being equal, excess weight raises risk of death from cancer from 9 to 62 percent. But in real life, all these factors could be related, because eating more vegetables or less fat, and exercising regularly may be part of how someone reaches or maintains a healthy weight. Since smoking has such strong cancer-causing effects, despite its association with lower weight, it can confuse the relationship of weight to cancer risk. So in trying to assess how many cancer deaths are truly related to excess weight, researchers used the proportion of cancer deaths linked to weight among those who have never smoked. On this basis, they concluded that current patterns of overweight and obesity in the United States could account for 14 percent of all deaths from cancer in men and 20 percent of those in women. That translates to 90,000 deaths a year that could be prevented if people maintained healthy weights.