Smoking, inactivity, being overweight, high blood pressure: you can probably name a few risk factors for heart disease but there's a good chance that depression won't be among them.
Although depression has been on the Heart Foundation's list of risk factors for heart disease for over a decade most of us don't realise the impact it can have on the health of our arteries or that the more severe the depression is the higher the risk.
"Depression is a risk factor that needs to be taken as seriously as any other - it's up there with smoking," says Professor Gavin Lambert, National Health and Medical Research Fellow at the Baker IDI Heart and Diabetes Institute.
"Not only is it a risk factor for developing heart disease, but it may also exacerbate existing heart disease - if you already have heart disease and go on to develop depression you're four times more likely to die within six months."
Depression isn't all in the mind. It can have a physiological effect on the heart by increasing the production of a stress hormone called noradrenaline released by the nerves involved in the 'fight or flight' response.
Releasing too much of this hormone over time can damage the blood vessels in a number of different ways, explains Lambert.
Like smoking, it can constrict the blood vessels making them narrower and more easily blocked.
It can raise blood pressure and cause other changes that increase the risk of plaque building up on blood vessel walls and it can trigger inflammation which can make it easier for clots to form.
All this wear and tear on blood vessels is independent of the other effects on heart health that can flow from depression - the low mood that can lead to other problems like smoking, drinking too much alcohol, poor diet, not bothering to exercise or take medication.
Lambert's research is trying to find out if some people with depression are more likely to develop heart disease because of their genes.
One in three people with depression, but no underlying heart disease, have an overactive fight or flight response that produces high levels of noradrenaline and which is thought to be linked to a gene.
His study aims to learn more about this gene and if the use of some anti-depressants (serotonin re-uptake inhibitors or SSRIs) can lower heart disease risk.
Some researchers also suggest that depression might be a consequence of heart disease - and not just because concerns about health might darken a person's mood.
"It's possible that there's also a physiological affect on the brain - your brain needs oxygen and nutrients like any other part of the body so if circulation is affected by disease it could have an impact on the brain," Lambert says.
"There's also a strong link between inflammation and heart disease and inflammation and depression. It could be that inflammatory chemicals that contribute to heart disease could also cause changes in the brain, but we don't know."
Still, it's not only the public that needs more awareness of depression's link to heart disease - the same goes for many doctors, says Professor James Tatoulis, the Heart Foundation's Chief Medical Adviser.
"If someone has heart disease very few doctors will screen them for signs of depression, and although people who have had a heart attack are usually seen by a physiotherapist and a dietitian in hospital for advice on exercise and diet they're not seen routinely by a psychologist or a social worker in relation to their mental wellbeing," he says.
But a new questionnaire developed by the Heart Foundation to help doctors spot symptoms of depression in patients with heart disease aims to change this.
Promoted at the World Congress of Cardiology in Melbourne last week, the questionnaire is designed to be used not just the first time a patient sees their doctor following a heart attack but at regular intervals afterwards.
What about people who have a diagnosis of depression but no history of heart disease?
"As doctors we should also be looking at their cardiac risk factors like high blood pressure and high levels of cholesterol," Tatoulis says.
For more information about heart disease and depression go to www.heartfoundation.org.nz
- Sydney Morning Herald
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