WEDNESDAY, June 18, 2014 (HealthDay News) -- Young and middle-aged women with depression are more than twice as likely to suffer a heart attack or die from heart disease as their mentally healthy peers, new research suggests.
The study also found that women younger than 55 are more likely than men or older women to become depressed.
Exactly what accounts for this relationship between mood disorder and heart disease in younger women isn't clear, said study lead author Dr. Amit Shah, an assistant professor of epidemiology with the Rollins School of Public Health at Emory University in Atlanta.
"These kinds of relationships are very complicated, and we're still investigating to better understand the reason," he said.
Still, the results fit into the "bigger picture," Shah added.
"We have known for some time that heart disease is actually the number one killer in women, and that heart disease does start at an early age," he said. "And it could be that younger women have neurobiological differences or hormonal differences that make them respond to acute mental stress differently than men or older women."
This could mean that when they have depression, they also have an elevated risk for heart disease, Shah said.
An association between depression and greater risk of death from heart disease was not seen among women over 55 or among men as a whole, the researchers noted.
A woman's lifetime risk for developing heart disease is upwards of 50 percent, according to background information in the study, published online June 18 in the Journal of the American Heart Association.
To explore the link between depression and heart risk, the team followed more than 3,200 men and women diagnosed with heart disease or suspected of having it between 2003 and 2010. Patients' average age was nearly 63, and one-third were women.
All of the study participants were scheduled for an arterial X-ray (a coronary angiography) to assess the presence of arterial disease.
After three years of follow-up, the investigators determined that women aged 55 and younger were the most likely to have struggled with moderate or severe depression.
The researchers found that 27 percent of them were clinically depressed. By contrast, depression was cited among just 9 percent of men 65 and older.
And while depression didn't appear related to heart disease risk among men of any age or elderly women, the team found that among women 55 and younger, every one-point rise in depression symptom ratings translated into a 7 percent rise in heart disease risk.
That meant that depressed young and middle-aged women faced a 2.17 times greater risk for experiencing a heart attack, or for needing an invasive procedure to widen their diseased arterial pathways.
The same women also faced similar elevated risk for dying from heart disease, and a 2.45 greater risk for dying from any cause during the study follow-up period.
"Although we have more work to better understand what's going on, what this means is that young depressed women should view depression as a motivating factor to live a healthier lifestyle and be more aggressive about preventive care," said Shah.
Because depression might undermine a woman's ability to obtain medical care, her friends, family and physicians may need to get involved and provide encouragement, he said.
Michael O'Hara, a professor of psychology at the University of Iowa in Iowa City, said researchers have long seen an association between heart disease and depression, among both males and females.
However, that association does not prove a cause-and-effect relationship.
"In general, depression increases the morbidity of many medical illnesses, including heart disease," O'Hara said. "For example, women and men who have depression after a heart attack often have poorer recoveries and are more likely to die."
Exactly why isn't clear. "We know that depression is associated with inflammatory processes and immune function," he said. "So there has been some thought that, in fact, depression compromises the body's ability to recover from illness."
Studies like this that strive to better understand the connection between depression and illness are very important for both men and women, O'Hara added.
For more about women and heart disease, visit the American Heart Association.