An article at Forbes takes a look at the effects of wealth on longevity, finding that a) it doesn't make much of a difference in the grand scheme of things and b) any meaningful analysis would have to take into account the host of selection effects. If you're smart and driven enough to get rich, you're probably also someone who takes care of your health.
The billionaires lived 3.5 years longer than average American males. The results would be even more dramatic if we took into account average life expectancies from around the world, since the billionaires on our list are of all different nationalities.
According to a 1999 study in the British Medical Journal, higher income is, in fact, "casually associated with greater longevity." But when it comes to living longer, billionaires may not be that much better off than mere millionaires. "While an extra dollar of income is protective," the study reads, "the amount of protective effect tails off as total income rises."
Some studies contend that rich live longer because of intellectual Darwinism. "Social status," Seligman writes, "correlates strongly and positively with IQ and other measures of intelligence, and intelligence correlates strongly with health literacy--the ability to understand and follow a prescription for disease prevention and treatment." This theory is not without evidence: Seligman cites a 2003 study by psychologist Ian Deary of the University of Edinburgh that found mortality rates to be 17% higher for each 15-point falloff in IQ.
Since most of what kills Americans today is chronic disease, health literacy may, in fact, be a key to longevity. Understanding and monitoring risk factors for the major conditions that predispose us to death--heart disease, cancer, diabetes, obesity, high blood pressure--requires a considerable amount of awareness, discipline and foresight.
In any case, simply having great wealth is not going to work wonders for your life span. You'll get a few extra years at most if all you are doing is enjoying the peripheral benefits. One of the hallmarks of this modern world is that the gap in consumer benefits enjoyed by the wealthy and the poor is not as large as you might think, nor as large as it once was. All the advances that would amaze a time traveller from the 1300s are largely available to the first world poor of our time.
There is one thing that wealth does bring, however, and that is the ability to effect change. Wealth is a big lever that can be used to shape the future - it would only take a small fraction of the holdings of the wealthiest 400 people in the world to set serious anti-aging research underway, for example. In other words, the best way to turn wealth into extra healthy years is to fund advances into working anti-aging and longevity medicine rather than simply enjoy the best medicine currently available. One of the goals of healthy life extension advocacy is to make that point clear to the wealthy of the world.