The one social factor that researchers agree is consistently linked to longer lives in every country where it has been studied is education. It is more important than race; it obliterates any effects of income.

Year after year, in study after study, says Richard Hodes, director of the National Institute on Aging, education “keeps coming up.”

And, health economists say, those factors that are popularly believed to be crucial — money and health insurance, for example, pale in comparison.

Dr. Smith explains: “Giving people more Social Security income, or less for that matter, will not really affect people’s health. It is a good thing to do for other reasons but

not for health.”

Health insurance, too, he says, “is vastly overrated in the policy debate.”

Instead, Dr. Smith and others say, what may make the biggest difference is keeping young people in school. A few extra years of school is associated with extra years of life and vastly improved health decades later, in old age.