May 29 (Bloomberg) -- This is a morbid column about some unexpected and encouraging news: Deep economic declines, such as the one we experienced in the U.S. a few years ago, probably lengthen life expectancy. This is exactly the opposite of what most people believe.

A reasonable estimate is that for every percentage-point increase in the unemployment rate, the U.S. mortality rate drops by 0.3 percentage point. In other words, and although it runs counter to our intuition, recessions may be bad for our wallets but good for our health.

Part of the reason is that there are fewer traffic fatalities. This makes sense because there’s typically less traffic when the economy slows down. From 2002 to 2007, the number of Americans dying in motor-vehicle accidents was roughly constant, at about 42,000 or so per year. By 2011, that figure had dropped by almost a quarter, to 32,367 -- the lowest since 1949, when the U.S. population was half what it is now.

Still, automobile accidents account for less than 2 percent of deaths each year, so the drop in these fatalities accounts for only a tiny part of why life expectancy improves during recessions.

The rest of the story may be explained by evidence found in three recent studies. One of these was about Iceland, which experienced a severe recession after its banking crisis in October 2008. During the bust, Icelanders abandoned various unhealthy behaviors, according to surveys conducted by the University of Iceland, Rider University and the Robert Wood Johnson Medical School in New Jersey in 2007 and 2009.

Better Behavior

Among working-age people, for example, the share who smoked fell to 19 percent, from 23 percent before the crisis. The proportion who consumed at least five alcoholic drinks in a day at least once a month declined to 17 percent, from 20 percent. The share eating fast food weekly fell to 25 percent in 2009, from 32 percent in 2007, and the figure for those practicing indoor tanning declined to 13 percent from 17 percent. Meanwhile, the proportion of people getting adequate sleep rose to 76 percent, from 72 percent.

The effects of these shifts apparently outweighed any negative effects of the crisis -- for example, the increasing share of Icelanders suffering from anxiety or poor mental health.

A second study focused on air pollution, specifically carbon monoxide, particulate matter and ozone. Higher concentrations of carbon monoxide are connected with higher mortality rates, economists Garth Heutel of the University of North Carolina at Greensboro and Christopher Ruhm of the University of Virginia found. A one-standard-deviation increase in carbon monoxide raises the mortality rate by 2 percent, they observed. As one would expect, this effect seems to be concentrated in deaths from respiratory and cardiovascular diseases.

Heutel and Ruhm demonstrate that about one-third of the effect of high unemployment on mortality can be attributed to less pollution: When the economy is in a recession, concentrations of carbon monoxide are lower, and this improvement in air quality benefits people’s health.

The third study found that deaths among the elderly decline disproportionately during a recession, and that the quality of nursing-home staff may be an important reason. Staffing ratios in nursing homes tend to be higher when the overall labor market weakens, because more people are willing to work in the facilities, this study found.

Taken together, the evidence suggests that a combination of forces contribute to the increase in life expectancy during times of higher unemployment: Motor vehicle deaths decline, people tend to avoid unhealthy behavior, air pollution is diminished, and nursing home staffing improves.

None of which should make us wish for economic trouble. Higher unemployment means loss of productivity, lower income and mental anguish, and those are more than sufficient reasons to combat joblessness. There may be some small consolation, though, in learning that it probably doesn’t harm human health the way that we all imagined.

(Peter Orszag is vice chairman of corporate and investment banking and chairman of the financial strategy and solutions group at Citigroup Inc. and a former director of the Office of Management and Budget in the Obama administration. The opinions expressed are his own.)

To contact the writer of this article: Peter Orszag at orszagbloomberg@gmail.com

To contact the editor responsible for this article: Mary Duenwald at mduenwald@bloomberg.net