Declining effect of latitude on melanoma mortality rates in the United States. A preliminary study.

The gradient of mortality from melanoma of the skin with latitude among US whites was estimated from the slopes of semilogarithmic models fitted to the state-specific mortality rates and the latitudes of the states' capital cities. The upward gradient of mortality from north to south for malignant melanoma of the skin has been decreasing since 1950-1959, when data first became available, through 1960-1969, 1970-1979, and 1988-1992. By the early years of the 21st century, rates of melanoma mortality in the contiguous United States are expected to be unaffected by latitude. For the country as a whole, melanoma mortality rates have been rising for many years. This rise has become progressively slower, such that national rates have been projected to stabilize in the near future. While increasing geographic mobility has probably played a role in reducing the latitude effect, melanoma mortality rates may have reached levels at which increased exposure of US whites to sunlight has little incremental effect.