Devra Lee Davis and others have developed a hypothesis about the cause of breast cancer in women. Now a second hypothesis has been developed by Devra Davis, Aaron Blair, Sheila Hoar Zahm, Neil Pearce, Joseph Fraumeni, and others at the National Cancer Institute, asking about the role of pesticides in certain cancers. The hypothesis begins by examining the health of farmers. Farmers are a relatively healthy group. For any given age, farmers have a low overall mortality rate, indicating general good health.
Farmers also have lower risks for cancers of the lung, esophagus, bladder, colon, liver, and kidney.
Low rates of cancer for lung, esophagus, and bladder, and low rates of heart disease, can be explained by low prevalence of smoking among farmers, which has been noted in numerous studies. In addition, farmers have a low percentage of body fat, and a high measure of physical fitness, probably because they perform hard physical labor that keeps them in good shape. This good physical condition probably contributes to lower risks for heart disease and colon cancer, both of which are associated with a sedentary lifestyle. Farmers also eat a relatively large amount of fruits and vegetables, compared to the average American, and relatively small amounts of processed foods. As a consequence, farmers' diets are most likely higher in fiber than the average diet.