Ms Lise Tuset Gustad, first author of the study and an intensive care nurse at Levanger Hospital in Norway, said: "We found a dose response relationship between depressive symptoms and the risk of developing heart failure. That means that the more depressed you feel, the more you are at risk."
She added: "People who have lost interest in things they used to enjoy, such as reading or watching a television series, may have the early signs of depression. It's a good idea to see your doctor in these early stages for some advice on how to reduce your depression levels."
This is one of the first large, prospective studies to investigate whether depression increases the risk of developing heart failure. Data were collected during the second wave of a large epidemiological study in Nord-Trøndelag county, Norway, called the Nord-Trøndelag Health Study (HUNT study). Nearly 63 000 of the 97 000 citizens in the county agreed to take part.
When the second wave of the HUNT study began in 1995, information was collected including body mass index, physical activity, smoking habits and blood pressure. Depression was assessed and ranked for severity using the Hospital Anxiety and Depression Scale. Every Norwegian citizen receives a unique 11 digit number at birth which is used at hospitals and the National Cause of Death Registry. The researchers used this number to track which patients were hospitalised with heart failure or died from heart failure during the 11 year study.
During the study period nearly 1 500 people developed heart failure. Compared to residents with no symptoms of depression, people with mild symptoms had a 5% increased risk of developing heart failure and those with moderate to severe symptoms had a 40% increased risk.
Ms Gustad said: "Depressive symptoms increase the chance of developing heart failure and the more severe the symptoms are, the greater the risk. Depressed people have less healthy lifestyles, so our analysis adjusted for factors such as obesity and smoking that could cause both depression and heart failure. This means we can be confident that these factors did not cause the association."
She added: "There is effective treatment for depression, particularly if people get help early. The early symptoms of depression include a loss of interest and loss of pleasure in things that have normally been interesting or given pleasure. If you feel like that, speak to your friends and if it lasts for a month see your doctor or nurse. Depression can be treated easily in the early stages and many people don't need medication. Talking to a professional may be all you need."
Ms Gustad continued: "Depression triggers stress hormones. If you're stressed you feel your pulse going up and your breath speeding up, which is the result of hormones being released. Those stress hormones also induce inflammation and atherosclerosis, which may accelerate heart diseases. Another mechanism could also be because depressed people find it more difficult to follow advice about how to take medications and improve their lifestyle."
She concluded: "Depression is disabling. It blocks people's ability to take their medications as prescribed, stop smoking, improve their diet or exercise more. Hospitals in Norway specialise in either somatic or psychiatric illness and there is little communication between them. Patients at all hospitals should be screened for depression to help them recover from existing illnesses, avoid developing new ones and have a more enjoyable life."