Just about everyone and his economist mother has researched the ways in which socioeconomic status correlates with health. In the United States, the fraction of people in 'excellent' or 'very good' health in the top income quartile hovers at around 40 percentage points above that in the bottom quartile. It doesn't take long to come up with all sorts of theories for this: varying access to health care, poor behavioral habits on the part of the poor, differing environmental factors, differing exposure to stressful events. But no one quite knows for sure.
Anyway, a new RAND paper by James P. Smith looks at this problem in greater detail, trying to figure out which aspects of socioeconomic status actually matter for health. For instance, he looks at the stock market gains during the 1990swhen many people became unexpectedly wealthyand suggests that income and wealth gains, by themselves, do not decrease the chance of disease onset. This may not be an ideal sample set, though, since those who gained in the stock market were already fairly well-off.
On the other hand, education correlates remarkably well with better health; perhaps in part, Smith suggests, because people with higher levels of education can better manage complicated treatment regiments. An experiment involving a diabetes treatment seems to suggest just that. (Programs that forced patients to stick to the regiment had large health-effects on the less-educated.) But as always, proving causation is another matterwhy are educated people, apparently, better at self-management? Maybe they're more likely to have jobs with more free time. Nevertheless, the "education effect" really is so significant, and persists even into old age.
Two other findings. First, Smith points out that the link between socioeconomic status and health may exist, in part, because the latter causes the former. The onset of a serious chronic disease, after all, really does take a pair of fists to a person's job and salary. So perhaps the "health gap" causes socioeconomic inequality, rather than the other way around. Second, and more importantly, a growing body of research suggests that economic circumstances during childhood seem to have a serious bearing on health later on in life. Still, no one knows exactly why, although theories abound. The importance of nutrition in the womb is one. Interesting fact: In the olden days, and even among current adults, life expectancy varied significantly with the season of birth. In the northern hemisphere, for instance, 50-year-olds who were born in October and Novemberand hence, whose mothers had access to cheap and plentiful fruits, vegetables, and eggs during pregnancycould expect to live about 3/4 of a year longer than those born in the spring. I don't know if that's still true for people growing up today, but it might be.