Older Americans who have symptoms of depression are as likely as those who smoke to develop a new disease within two years, according to a U-M study of more than 6,000 Americans age 70 and older.
The study, presented last month at the annual meeting of the Gerontological Society of America, was conducted by Caroline S. Blaum, assistant professor of internal medicine. It is based on data from the U-M Health and Retirement Study, funded by the National Institute on Aging.
The relationship of depression, disease and disability is complex, says Blaum, who is also an assistant research scientist at the Institute of Gerontology. Not only do disease and disability lead to depressed symptoms, but depressive symptoms seem to be a precursor of the development of future disease. This effect is seen with relatively mild depressive symptoms such as decreased energy and restless sleeping, not just severe clinical depression.
To evaluate the link between disease and depressive symptoms, Blaum analyzed data collected from the same older people in 1993 and 1995. The population-based study of the assets and health dynamics of the oldest old contains extensive information on physical, mental, financial and emotional health, as well as a wide range of demographic and behavioral information for a nationally representative sample of Americans born in 1923 or before.
At the start of the study, the average age of respondents was 77. Approximately 62 percent were female and 87 percent were white. Respondents had an average of 2.1 chronic diseases each. Between 1993 and 1995, Blaum found, 48 percent reported that they had developed new diseases, while 52 percent had the same self-reported disease burden they started the study with.
Controlling for gender, marital status, education, the number of diseases at the start of the study, and the presence of mental or sensory impairments and disabilities, Blaum analyzed how age, race, body mass index, smoking, physical limitations and depressed symptoms were related to the odds of developing a new disease during the two-year period. The types of diseases included the most common chronic conditions of older adults, such as diabetes, stroke, arthritis and cardiac disease.
Physical limitations, such as limitations in the ability to walk several blocks, climb stairs or lift a 10-pound object, were the strongest predictors that a person would develop a new disease two years later, increasing the odds of developing at least one new disease by nearly 50 percent.
But older people who smoked or had multiple symptoms of depression, such as feeling lonely or sad in the past week, were 34 percent more likely than those who did not to develop new disease, according to Blaums analysis. Older people with a high body mass index, a widely used indicator of obesity, were 18 percent more likely to develop a higher disease burden in the following two years.
Other recent studies have suggested that depression and depressed symptoms are risk factors for cognitive decline and cancer, says Blaum. This study suggests that depressed symptoms may represent pre-clinical indicators of a wide range of future diagnosed diseases. Along with obesity and smoking, depressed symptoms may be a potentially modifiable risk factor for increased disease burden in older people. Clinical trials are needed to find out whether treatment of mild depression leads to decreased disease burden and improved function in older adults.