Indirect evidence that ultraviolet-B radiation mitigates multiple sclerosis in the United States.

This article describes on the relationship of the relative prevalence of persons dying with multiple sclerosis with the latitude of the population centroid of those affected in each of the United States. Regression to zero prevalence occurs at the Tropic of Cancer, the latitude where the Sun is at zenith on the summer solstice and where ultraviolet radiation (UVR) is least attenuated. This observation supports UVR as a mitigating force in multiple sclerosis.