I read with more than usual interest the article on Leadville, Colorado (“Silver City,” April issue). Although I have never had the privilege of visiting Leadville, for years I referred to the city in my lectures at Harvard University. I say this because, spending their lives at 10,200 feet, Leadville’s inhabitants receive the highest dose from cosmic radiation of any large group of people living anywhere in the United States: Their annual dose is more than double that in nearby Denver and four times that in lower-lying cities, such as New York, Miami, Los Angeles, and Seattle.

In fact, the annual cosmic radiation dose in Leadville is five times the federal limit for people living near a commercial nuclear power plant. Interestingly enough, extensive studies of populations receiving these higher doses have never revealed any health effects whatsoever.