Geographic mappings of colorectal cancer rates: a retrospect of studies, 1974-1984.

Geographic mapping of colorectal cancer rates revealed areas with high rates as well as areas with low rates. Comparisons between high-rate areas and areas deficient in selenium led to animal experiments that showed that selenium could reduce chemically induced intestinal tumors. A low-rate area was found to be geochemically unique with soil and water rich in potassium. This led to a series of studies indicating that elevated intracellular potassium reduces cancer risks, while elevated intracellular sodium increases the risks. Variance-reducing techniques and methods for statistical evaluation of clusters were obtained as spinoff results.