The same relationship was not found among blacks or Hispanics, although this may be due to limitations in the tool used to assess depression, according to lead study author Ji Chong, MD, Clinical Stroke Fellow at the Neurological Institute, Columbia Presbyterian Medical Center in New York, New York.
"Studies have found depressive symptoms to be a risk factor for stroke," said Chong, "but it is not clear if greater levels of depression confer greater risk." To answer this question, she and her colleagues collected data from almost 3,300 subjects who were part of the Northern Manhattan Study, a long-term investigation of risk factors for stroke, myocardial infarction, or vascular death. The subjects in the study had a mean age of 69 years, and were 21 percent white, 24 percent black, and 52 percent Hispanic.
Presence of depressed mood was determined by the question, "What has your mood been like this past week," with answers ranging from 0 (no depressed mood) to 4 (severe depressed mood). The question is part of the Hamilton Depression Inventory, a widely used clinical measure of depression. At baseline, 33 percent of the entire cohort reported some level of depressed mood, including 32 percent of whites, 25 percent of blacks, and 38 percent of Hispanics.
During a follow-up period of almost five years, 160 ischemic strokes occurred. Any level of depressed mood was associated with a 40 percent higher risk for stroke among the entire cohort, with a slight increase of risk for moderate to severe symptoms versus minor symptoms.
When the results were stratified by ethnicity, no effect of mood was seen on stroke risk for either black or Hispanic subgroups. In contrast, for whites, any level of depressed mood more than doubled the risk of stroke, with a very strong effect of severity on risk--those with the most severe symptoms had more than four times the risk for stroke as those with no symptoms.
"Depressed mood is an independent predictor of stroke," Chong concluded, "and in whites, greater severity of symptoms is associated with a higher risk of stroke." She suggested that the ethnic differences found in this study may be more related to cultural differences in interpretation of the question, rather than biological differences among subgroups. "It remains to be seen whether early treatment of depression can modify the risk for later stroke," said Chong.
The study was supported by funding from the National Institute of Neurological Disorders and Stroke.
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Editor's Notes: Dr. Chong will present this research during a scientific session at the 56th Annual Meeting at 3:15 p.m. PT (6:15 p.m. ET) on Wednesday, April 28 in Room 310 of the Moscone Convention Center.