Low-income people with depression are less likely to respond to treatment and more likely to be suicidal than those who have higher incomes, according to a study in the January issue of Archives of General Psychiatry, one of the JAMA/Archives journals.

Socioeconomic factors, including income, education and occupation, have long been linked to health status, illness and death. Research has shown that people with lower socioeconomic status (SES) are more likely to develop a depressive illness and that their depression is more severe than that of people higher on the SES scale. Several studies have hypothesized that socioeconomic factors, including income and education, would also affect how people respond to medications and other therapies for depression, but have ultimately proved inconclusive, according to background information in the article.

Alex Cohen, Ph.D., of Harvard Medical School, Boston, and colleagues reanalyzed two previous clinical trials funded by the National Institute of Mental Health and conducted at the University of Pittsburgh.

The 248 participants were all 59 years or older and receiving antidepressant medications combined with psychotherapy. Their education levels were assessed at the beginning of the original studies. Median annual household income for their areas was obtained from the U.S. Census Bureau. Low-income was defined as less than $25,000, middle-income between $25,000 and $50,000 and high-income more than $50,000. The subjects’ depressive symptoms and response to treatment were measured weekly.

When the authors controlled for demographic factors, such as age and gender, and baseline clinical characteristics, including recurrence of depression and age at onset, they found that people in areas defined as middle-income were significantly more likely to respond to treatment than those in the low-income group. High-income people were only marginally more likely to respond to treatment than middle-income residents, but as a group, high- and middle-income study participants were significantly more likely to respond than those in low-income areas.

In addition, people in low-income areas were about twice as likely as those in middle-income areas and two and a half times as likely as those in high-income tracts to be suicidal, “suggesting an inverse relationship between the median household income of the neighborhoods in which subjects resided and suicidality,” the authors write.

The authors found that years of education did not affect treatment response or suicidality in this particular study group. “When the older subjects in our study came of age, economic and social success in the industrial economy was not so dependent on education,” they write. “Thus, we speculate that years of education is a less accurate measure of SES in this sample.”

Based on their findings, the authors “suggest that future clinical trials routinely gather data on individual income, educational degrees earned, occupation and aspects of the broader social environment such as social capital. However, to transform evidence into knowledge that will inform the treatment of depression, it is essential that future research examines all of the factors (for example, neighborhoods, stress, social support, race/ethnicity or income inequalities) that may mediate the association between SES and clinical outcomes.”

(Arch Gen Psychiatry. 2006;63:50-56. Available pre-embargo to the media at http://www.jamamedia.org.)