A study by researchers at the University of Bergen, Norway, and the Institute of Psychiatry (IoP) at King's College London has found that depression is as much of a risk factor for mortality as smoking.
Utilising a unique link between a survey of over 60,000 people and a comprehensive mortality database, the researchers found that over the four years following the survey, the mortality risk was increased to a similar extent in people who were depressed as in people who were smokers.
Dr Robert Stewart, who led the research team at the IoP, explains the possible reasons that may underlie these surprising findings: 'Unlike smoking, we don't know how causal the association with depression is but it does suggest that more attention should be paid to this link because the association persisted after adjusting for many other factors.'
The study also shows that patients with depression face an overall increased risk of mortality, while a combination of depression and anxiety in patients lowers mortality compared with depression alone. Dr Stewart explains: 'One of the main messages from this research is that 'a little anxiety may be good for you'.
'It appears that we're talking about two risk groups here. People with very high levels of anxiety symptoms may be naturally more vulnerable due to stress, for example through the effects stress has on cardiovascular outcomes. On the other hand, people who score very low on anxiety measures, i.e. those who deny any symptoms at all, may be people who also tend not to seek help for physical conditions, or they may be people who tend to take risks. This would explain the higher mortality.'
In terms of the relationship between mortality and anxiety with depression as a risk factor, the research suggests that help-seeking behaviour may explain the pattern of outcomes. People with depression may not seek help or may fail to receive help when they do seek it, whereas the opposite may be true for people with anxiety.
Dr Stewart comments: 'It would certainly not surprise me at all to find that doctors are less likely to investigate physical symptoms in people with depression because they think that depression is the explanation, but may be more likely to investigate if someone is anxious because they think it will reassure them. These are conjectures but they would fit with the data.'
The researchers point out that the results should be considered in conjunction with other evidence suggesting a variety of adverse physical health outcomes and poor health associated with mental disorders such as depression and psychotic disorders.
In light of the findings, Dr Stewart makes suggestions on the focus of future developments in the treatment of depression and anxiety: 'The physical health of people with current or previous mental disorder needs a lot more attention than it gets at the moment.
'This applies to primary care, secondary mental health care and general hospital care in the sense that there should be more active screening for physical disorders and risk factors, such as blood pressure, cholesterol, adverse diet, smoking, lack of exercise, in people with mental disorders. This should be done in addition to more active treatment of disorders when present, and more effective general health promotion.'
Notes to editors
Arnstein Mykletun, Ottar Bjerkeset, Simon Øverland, Martin Prince, Michael Dewey and Robert Stewart: Levels of anxiety and depression as predictors of mortality: the HUNT study. The British Journal of Psychiatry (2009) 195: 118-125. The full paper can be accessed on http://bjp.rcpsych.org/cgi/content/abstract/195/2/118.
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The British Journal of Psychiatry