The economic downturn may not be good for your bottom line, but it might be a boon to your health, a study on health trends during the Great Depression suggests.

Looking at U.S. death rates between 1920 and 1940, researchers found that during the bleakest years of the Great Depression, death rates dipped when compared with years of economic expansion. The patterns were seen among men and women, and across age groups.

At the same time, life expectancy generally increased during the recession years and declined during years of growth.

The findings, published Monday in the Proceedings of the National Academy of Sciences, may seem counterintuitive.

However, they add to previous research showing correlations between economic woes and health improvements in various countries.

Many people may assume that the health of the general population takes a hit during recession, noted lead researcher Dr. Jose A. Tapia Granados, an assistant research scientist at the University of Michigan in Ann Arbor.

"But it is very clear that this is not the case," he told Reuters Health.

This study could not look at the reasons why. However, Tapia Granados speculated on some potential factors.

Economic expansions have been linked to population increases in smoking and drinking, as well as less sleep and more stress.

At least some of these factors could have immediate effects on mortality rates, Tapia Granados said. If a person with underlying heart disease begins to smoke more, for example, that could raise his or her short-term risk of heart attack.

In addition, as the economy picks up, so does roadway traffic — which also means more traffic deaths. Fatal workplace injuries show a similar increase.

Increased industrial production and road traffic also create more air pollution, Tapia Granados said. He noted that studies have shown that deaths from heart disease tend to spike on days marked by heavy air pollution.

In their study, Tapia Granados and his colleagues found that during years of strong economic growth — including 1923, 1926, 1929 and 1936-1937 — overall death rates were higher, and deaths from heart disease and tuberculosis peaked.

In contrast, during the early 1930s, which were the main years of the Great Depression, death rates declined, while life expectancy rose — from age 57 in 1929 to age 63 in 1933, followed by a temporary decline in 1936.

The difference was most striking among non-white Americans, the researchers found. Between 1921 and 1926, these men and women lost roughly eight years in life expectancy, but during the Great Depression, they gained an equivalent number of years.

When the researchers looked at specific causes of death, they found that deaths from five of the six top U.S. killers remained stable or decreased during the Depression. The one exception was deaths from suicide.

"For this reason," Tapia Granados said, "suicide prevention is particularly important today."

He said that he and his colleagues plan to investigate some of the potential reasons why, outside of suicide, recessions may have health benefits. One focus will be the possible role of decreased air pollution.

Another will be the role of work-related factors, Tapia Granados said, including the question of whether longer hours, faster-paced work and sleep deprivation take a health toll during economic good times.