Something strange is going on in medicine. Major diseases, like colon cancer, dementia and heart disease, are waning in wealthy countries, and improved diagnosis and treatment cannot fully explain it.
Scientists marvel at this good news, a medical mystery of the best sort and one that is often overlooked as advocacy groups emphasize the toll of diseases and the need for more funds. Still, many are puzzled.
"It is really easy to come up with interesting, compelling explanations," said Dr. David S. Jones, a Harvard historian of medicine. "The challenge is to figure out which of those interesting and compelling hypotheses might be correct."
Of course, these diseases are far from gone. They still cause enormous suffering and kill millions each year.
But it looks as if people in the United States and some other wealthy countries are, unexpectedly, starting to beat back the diseases of aging. The leading killers are still the leading killers — cancer, heart disease, stroke — but they are occurring later in life, and people in general are living longer in good health.
Colon cancer is the latest conundrum. While the overall cancer death rate has been declining since the early 1990s, the plunge in colon cancer deaths is especially perplexing: The rate has fallen by nearly 50 percent since its peak in the 1980s, noted Dr. H. Gilbert Welch and Dr. Douglas J. Robertson of the Geisel School of Medicine at Dartmouth and the Veterans Affairs Medical Center in White River Junction, Vt., in a recent paper.