Latitudinal variation of digestive tract cancers in the US and China.

Latitude influences the availability of fresh fruits and vegetables (which are associated with cancer protection) and the use of food preservation methods (which are associated with increased cancer). Such dietary differences might be reflected in the frequency of death from cancer of the digestive tract. Female mortality rates for states and provinces of the US and China, both of which cover a wide latitude range, were chosen to investigate latitude- and time-related changes. Mortality for cancer of the stomach, liver, and rectum did increase with latitude in both nations, which is consistent with the hypothesis. Exceptions were cancer of the colon and esophagus; these cancers had a variable association with latitude and did not decline markedly in the US by 1970-1979 as did mortality rates from cancer of the other digestive tract sites. Increased refrigeration and improved transportation, both of which result in increased consumption of fresh fruits and vegetables, and decreased use of older food preservation methods may be responsible for the US decline in mortality rates from stomach, liver, and rectal cancers.