"We've known for a number of years that depression increases the risk of mortality as well as morbidity [illness] after a heart attack for at least three to six months," said study author Robert M. Carney, a professor of psychiatry at Washington University School of Medicine in St. Louis. "We assumed that we would find a decline in risk, but that was not what we found. The risk remained worse after five years."
Carney and his colleagues followed more than 750 people after their heart attacks, according to their report in the current online issue of the Journal of Affective Disorders. Using diagnostic interviews rather than the self-reporting common in most such studies, the researchers determined that 163 had major depression, and 195 had minor depression. Over the five-year study, the death rate was 87 percent higher for those with major depression and 76 percent higher for those with any form of depression.
In real numbers, 62 people diagnosed with depression died during the study, while 44 non-depressed heart attack patients died.
Why depression should increase the risk of dying is a mystery, Carney said. "We think that because depression is a chronic and recurrent problem, the factors causing that risk recur over time," he said. "But we don't know the mechanism."
The researchers have started a trial to determine whether the omega-3 fatty acids that are found in fish oil can reduce that risk. Heart patients are being given an antidepressant drug and a special formulation of omega-3 fatty acids, comparing them with a similar group that gets only an antidepressant.
"A number of studies over the years have found an inverse relationship between the amount of fish people eat and depression," Carney said. "The advantage of giving them in heart disease is that they have an effect on the cardiovascular system as well."
The major finding of the study and the use of omega-3 fatty acids are already in the mainstream of research on depression and heart disease, said Dr. Alexander H. Glassman, a professor of psychiatry at Columbia University Medical Center in New York City.
"There is a torrent of information that depression in relation to vascular disease worsens the outcome," Glassman said. "If you look at post-stroke patients, you find the same data. If you look at heart failure, depression has a similar effect on mortality."
The value of the study is that it had the longest follow-up of any trial using diagnostic interviews, which are regarded as more accurate than self-reporting, Glassman said. "It makes the evidence firmer and extends the evidence," he explained.
The use of omega-3 fatty acids is "a hot issue," being tried in cardiac and non-cardiac cases, Glassman said. "It is a logical thing to do," he added.
The study and the omega-3 trial will still leave some major issues about depression and heart disease open, Glassman said.
"The two key questions that remain are: Does treating depression make the outcome better? And what is it about depression that is causing the problem in the first place?" he said.
More information
Advice on depression after a heart attack is offered by the American Academy of Family Physicians.