The deadliest diseases in the U.S. are becoming less deadly—but no one knows why

Cancer, heart disease, dementia—the deadliest of all deadly diseases. They kill millions of people every year in the U.S., but those death rates are still far smaller than the rates for the same diseases only decades ago, according to multiple surveys.

An article in the New York Times called this phenomenon “a medical mystery of the best sort,” because no one knows exactly why or how these diseases are slowly releasing their strangleholds on the American healthcare system and its patients.

For example, every 10 years since 1977 has seen a 20 percent reduction in dementia-related deaths. Deaths from heart disease are 60 percent down from their high 50 years ago.

Advanced screening, dropping smoking rates and new innovations in treatment can explain a lot of the improvements, but these factors don't explain the total decline, experts told the New York Times. And no one knows what those other factors are.

Check out the New York Times for the whole story, including theories about cellular changes that could be causing these surprising trends.