Dr. Smith also asked whether getting richer made people healthier, an effect that could translate into a longer life. It does not, he concluded after studying the large increases in income during the stock market surge of the 1990s.

“I find almost no role of financial anything in the onset of disease,” Dr. Smith says. “That’s an almost throw-you-out-of-the-room thing,” he confesses, but the data, he and other economists insist, is consistent.

Income, says Dr. Preston, “is so heavily influenced by health itself.”

Much More Than Genes and Luck

As director of the National Institute on Aging, Dr. Hodes often speaks to policy makers, giving briefings on the latest scientific findings. But, he and others say, all too often there is a disconnect.

There are some important findings: Health and nutrition early in life, even prenatally, can affect health in middle and old age and can affect how long people live.

For the most part, genes have little effect on life spans. Controlling heart disease risk factors, like smoking, cholesterol, blood pressure and diabetes, pays off in a more vigorous old age and a longer life. And it seems increasingly likely that education plays a major role in health and life spans.

And then there is the question of what to do. It might seem logical to act now, pouring money into education or child health, for example.

But scientists often say they would like good evidence beforehand that a program that sounds like it would make a difference, like keeping students in school longer, really works. And if the goal is longer and healthier lives, is that the most cost-effective way to spend public money?