There is little doubt that depression is bad for the heart. Much as fatty diets, cigarette smoking, inactivity and obesity are linked with an increased risk of heart disease, recent evidence suggests that mental health has a similarly powerful impact. The question has always been, why?
Now, researchers provide the first data that may explain the association. Published in the Journal of the American Medical Association, the findings suggest that depression contributes to heart disease indirectly — by fostering unhealthy behaviors like smoking — rather than directly. Certain biological factors linked with depression, such as inflammation and the levels of brain chemicals like serotonin, may play some role in heart health, researchers say, but the new study found that the factors that most increased heart disease risk in depressed people were the ones you might expect: lack of exercise and smoking.
"We looked at all sorts of biological markers that could potentially play a role in linking depression and heart disease," says Dr. Mary Whooley, an internist at the VA Medical Center in San Francisco, and lead author of the new study. "We measured all of those, and found that they did not explain the association. All we needed to do was to ask the patient how much they were exercising to be able to explain the link."
Whooley studied more than 1,000 patients with heart disease at the VA for nearly five years. The patients filled out regular questionnaires to determine their mood state, and were asked yearly to report on any heart-related events. Researchers took blood and urine samples to measure their levels of omega-3 fatty acids, cortisol and the inflammatory marker C-reactive protein, as well as the neurotransmitters serotonin and norepinephrine — all agents that may be involved in both depression and heart disease. In all, about 20% of the participants reported depressive symptoms; over five years, those patients had a 50% higher rate of additional heart problems, compared with their non-depressed peers.
Whooley’s team studied the depressed group further. Researchers systematically adjusted for each potential risk factor to figure out whether it was mediating the link between depression and heart disease. Physiological factors, such as serotonin levels or CRP, for example, appeared not to have much impact. But when researchers adjusted for physical activity — that is, when they analyzed the data by assuming identical levels of exercise in both depressed and non-depressed patients — the difference in heart disease risk between the groups disappeared. Indeed, inactivity among the depressed patients gave them a 44% greater risk of having a heart event than people who were not depressed, accounting for nearly all of the depressed patients’ 50% higher risk. Picking up the remainder of the increased risk was cigarette smoking.
The findings suggest that the effect of depression on heart health may have less to do with changes in hormones or other biochemical pathways, and more to do with behavior. Compared with other people, notes Whooley, the depressed are less healthy overall — they’re less likely to exercise or take their heart medications, and are more likely to smoke. The relationship also feeds back on itself; previous studies show that exercise not only improves cardiovascular health, but also elevates mood and can ease depression.
The study may even help to explain why treating depression alone — rather than addressing patients’ mental state and accompanying behavioral changes — has not proven successful in reducing the risk of heart disease. "We have always looked at certain behaviors like physical activity and smoking in isolation with respect to their effect on heart disease," says Dr. Clyde Yancy, president-elect of the American Heart Association and medical director of the heart and vascular institute at Baylor College of Medicine. "But one or both could be manifestations of depression, which in turn leads to heart disease."
And while researchers are intrigued by the question of which comes first — depression or heart disease — the study points out that, in practice, it doesn’t really matter. "It’s hard to tease out which came first," says Whooley. "But our bottom line is that regardless of which is coming first, this study introduces a new pathway that might get at that risk, by focusing not so much on depression itself, but by getting at the behaviors that go along with depression." It may be easier to take Prozac than to take a jog, but as the study suggests, it may not always be as effective.
“大家查询或许会使抑郁和心脏病联系起来的各项生理指标,” Mary Whooley大夫,美国旧金山弗吉尼亚州医学中心的内科大夫,该项新研究的领导者说: “大家测试所有些人,发现他们不可以说明它们之间的联系。大家所要做的是询问患者有多少经验可以讲解这之间的联系。 ”
近五年来,在弗吉尼亚州医学中心,Whooley研究了多达1000个心脏患者,患者按期填一项调查表,有关他们的情绪状况,近年来有没任何心脏方面的问题。被研究者采了血液和尿液样本,以测量他们的omega – 3脂肪酸水平,皮质醇和炎症标志物C反应蛋白,与神经递质血清素和去甲肾上腺素,所有被研究者都患有抑郁症和心脏病。在所有人中,约有20 %的人报告有忧郁症状;5年后,与没抑郁症的人相比较,这类病人会额外有50 %较高的心脏问题的风险。
这项研究甚至可能能够帮助讲解为何单独治疗抑郁症-而不是针对患者的心理状况和相应的行为变化治疗-降低患心脏病的风险方面是不成功的。 “大家一直期待在某些行为,如运动和抽烟影响心脏病方面是孤立的,”Clyde Yancy大夫说,美国心脏协会当选会长和贝勒医学院心血管研究所主任。 “但,一方或双方可能证明抑郁会致使心脏疾病。 ”
而研究者们好奇的是,抑郁和心脏病哪一个先出现-研究报告指出,事实上没有哪个先哪个后的问题。 “非常难说什么是先出现的 ” Whooley说, “但,大家的原则是,无论哪一个先出现,该研究介绍了一种可能有的风险的新渠道,对抑郁症状本身并不太重视,把病人的行为和抑郁症一块治疗。”它可能更容易解决问题,而不是慢慢解决,但研究表明,这种办法可能不一直有效。