ANN ARBOR—Poverty and economic hardship are like poison. The more “doses” people encounter over time, the greater their odds of developing serious physical and mental health problems, according to a 29-year epidemiological study from the University of Michigan School of Public Health.

The study, which included lower income groups such as the working poor as well as those in poverty, appears in the Dec. 25 issue of the New England Journal of Medicine. The researchers examined data on income and health risk factors for more than 1,000 adults in Alameda County (Calif.) in 1965, 1974, 1983, and related their findings to physical, psychological, social and cognitive functioning in 1994.

John W. Lynch, assistant research scientist, U-M Department of Epidemiology, and George A. Kaplan, professor and chair of the department, reported that there was “a strong dose-response relationship” between the number of times people experienced economic hardship and the development of health and psychological problems.

Economic hardship was defined in the study as having a household income of twice the poverty line. For instance, the poverty line in 1965 was $3,317 so those whose household incomes fell below twice that amount?that is, fell below $6,634?were experiencing hardship. Twice the poverty line in 1974 and 1983 was $11,000 and $20,356, respectively. Dose-response effect on cognitive functioning: Men and women who experienced one “dose” of economic hardship in either 1965, 1974 or 1983 were 1.19 times as likely to report difficulties with cognitive functioning in 1994. Those who reported two doses were 2.28 times as likely to experience cognitive difficulties, and those who reported three doses were 4.6 times as likely to report cognitive difficulties in 1994. Dose-response effect on physical functioning: Those who reported one “dose” of hardship in either 1965, 1974 or 1983 were 1.49 times as likely to report difficulties with the activities of daily living in 1994. Those who experienced two or three doses were 1.85 and 3.79 times as likely to report difficulties with activities of daily living, respectively, in 1994. Dose-response effect on depression: Those who reported one “dose” of hardship were in 1965, 1974 or 1983 were 1.1 times as likely to report having symptoms of depression in 1994, while those who reported two or three doses were 1.72 and 3.24 times as likely to report symptoms of depression, respectively, in 1994.

“Notably, in addition to being more than three times as likely to experience depression, those who reported three doses of hardship were 5.09 times as likely to be cynically hostile and 5.6 times as likely to lack optimism as those who reported no hardship,” Lynch said.

“Finding a dose-response relationship between economic hardship and health among vulnerable, low income people, struggling to survive in volatile, economic times, has important implications for public health, health care and economic policy,” he added.

“The uncertainties surrounding welfare reform, the transition to managed health care, high levels of income inequality in the United States, and reduced access to medical care for the poor are likely to have serious short- and long-term public health consequences and must be monitored closely.”

Sarah J. Shema of the Human Population Laboratory, Public Health Institute, Berkeley, Calif., collaborated with Lynch and Kaplan on the study, which was funded by the National Institute on Aging.

Department of EpidemiologyPublic Health InstituteU-M News and Information ServicesUniversity of Michigan