News Opinion Commentary Effects of stress not truly understood Stressed out Stressed out Laurence Mouton / Getty Images Although a new study raises doubts about unhappiness and stress having negative health effects, a closer look at the study shows stress can't be eliminated as a factor in shortening life spans. Although a new study raises doubts about unhappiness and stress having negative health effects, a closer look at the study shows stress can't be eliminated as a factor in shortening life spans. (Laurence Mouton / Getty Images) -- And while differential trends in smoking and other habits partly explain the life-span gap, it's mostly a puzzle. I suspect that a major factor is stress — that prolonged exposure to stress has risen more among families of moderate income than it has among those of high income, and that the stress is literally killing people. A new study raises doubts about this hypothesis. The researchers found -- The researchers concluded that the women in worse health had shorter life expectancy, and that their health problems were also what caused them to feel stress and unhappiness. As the lead author, Bette Liu of the University of New South Wales, commented, "Illness makes you unhappy, but unhappiness doesn't make you ill." That would certainly undercut the idea that stress is a killer — were it not for three things that got almost no attention in the press coverage of the study. -- happiness and health for men than for women. Second, if unhappiness and stress do affect health, they may begin to do so well before the age of 50. In that case, when the authors of the British women study adjusted for self-reported health at the start of -- who, at the beginning of the study, had cancer, heart disease, stroke or chronic obstructive airways diseases. But to the extent that unhappiness and stress before age 50 could contribute to those conditions, the point is even stronger.) The authors of the British study did find that, after age 50, there is effectively no association between life span and happiness or stress. Indeed, this is perhaps their strongest finding and understandably raises questions about how unhappiness affects health. -- reported being in excellent health when the study started may well be exceptions for whom unhappiness imposes no harm. Other research from Britain shows that the harm from stress depends a lot on one's beliefs about it. If you're under stress but believe it doesn't affect your health, it doesn't. And if you believe it does, it does. This was true among subjects who rated their health as good as well as those who rated it as poor. So it's entirely possible that the unhappy women in the more recent study who were in excellent health view the effects of their unhappiness and stress differently than other unhappy, stressed people do. Given that we still don't know what's widening the life-span gap, and that stress cannot be eliminated as a possible factor, the academic and medical communities need to explore much more aggressively how stress affects different people.