'Depression linked to higher chance of dying from cancer,' The Independent reports. Analysis of English and Scottish data found a link between mental distress and cancer mortality, which remained even after other factors such as smoking were taken into account.
However, you definitely should not assume this means lots of people with mental health problems will get cancer, or that mental distress causes cancer.
The researchers say that only 8% of people with mental distress went on to die from colorectal cancer, one of the more common cancers.
There are a lot of reasons why mental health might affect the risk of death from cancer. The researchers tried to take account of some of these, for example links with smoking and exercise. But they didn’t have information about other factors, such as decisions to seek help for cancer symptoms. People with mental distress might get diagnosed later, or be less inclined to go along with treatment.
Possible biological links to cancer include raised levels of inflammation in the body due to psychological stress.
An important point the study does raise is that physical health and mental health are connected at a fundamental level. Poor mental health can affect you physically and vice versa.
Where did the story come from?
The study was carried out by researchers from University College London, Edinburgh University and the University of Sydney and had no specific funding. The study was published in the peer-reviewed British Medical Journal (BMJ) on an open-access basis, so it’s free to read online.
The Mail Online, The Sun and The Independent produced broadly accurate coverage of the study, although the reporting tended to overstate the findings, suggesting that anxiety and depression were big risk factors for cancer.
The Daily Telegraph misunderstood the study entirely, saying that 'the people who were most distressed by their diagnosis were 32 per cent more likely to die from their cancer' and 'staying positive could be the best way to fight the disease'.
However, the study looked at the mental health of people who had not been diagnosed with cancer, and recorded their chances of dying of cancer during an average 10 years follow-up. It didn't look at people’s responses to diagnosis, or whether they were 'feeling worried or withdrawn' as the Telegraph reports. And the claim 'staying positive could be the best way to fight the disease' is arguably both insensitive and insulting as it implies people who died of cancer were somehow 'not trying hard enough'.
All four media outlets used 'head-clutcher' photographs – images of people holding their head in their hands – to illustrate their stories. The organisation Time to Change, which challenges mental health stigma, has called for media to use other, less clichéd images to illustrate stories about mental health.
Such images reinforce the mistaken impression that depression and anxiety are conditions that usually cause noticeable physical symptoms, or can cause disordered patterns of thinking. In many cases, people with either condition can appear healthy to others.
What kind of research was this?
This was a meta-analysis of data from 16 prospective cohort studies. The studies all measured mental health at one point in time, then followed up what happened to people for an average of 10 years, including whether they died of any type of cancer.
This type of study can show links between factors - in this case between mental distress and later death from cancer - but cannot show that one factor causes another.
What did the researchers do?
Researchers used individual patient data from 16 population-based studies of adults aged 16 or over in England and Scotland. The studies, carried out between 1994 and 2008, asked people a range of questions, and included a psychological distress questionnaire. People were also asked if they were happy to have their records linked to a cancer death registry (and cancer diagnosis registry in Scotland).
The researchers looked at records for people who'd filled out the psychological distress questionnaire and agreed to be in the cancer registration scheme, to see if there was a link between mental distress and death from cancer.
The questionnaire (general health questionnaire, or GHQ12) asks 12 questions to assess whether people have symptoms of anxiety or depression. People are divided into four groups depending on their answers, from no symptoms at all to a high level of symptoms. However, it’s not the same as being diagnosed with anxiety or depression.
Researchers wanted to see whether specific types of cancers were more or less linked to mental health, so they did their analysis for each type of cancer registered (where there were 50 deaths or more) as well as for overall cancer deaths.
They adjusted the figures to take account of potential confounders, such as:
- body mass index
- educational attainment
- alcohol consumption
They did various sensitivity analyses, and discounted people who died within five years, to avoid the possibility that people's mental distress was caused by undiagnosed cancer.
What were the basic results?
People with highest levels of mental distress, compared to those with lowest levels of distress, were more likely to have died from:
- colorectal cancer (hazard ratio (HR) 1.84, 95% confidence interval (CI) 1.21 to 2.78)
- prostate cancer (HR 2.42, 95% CI 1.29 to 4.54)
- pancreatic cancer (HR 2.76, 95%Ci 1.47 to 5.19)
- oesophageal (gullet) cancer (HR 2.59, 95%CI 1.34 to 5)
- leukaemia (HR 3.86, 95% CI 1.42 to 10.5)
Looking at all types of cancer combined, people with highest levels of mental distress were 32% more likely to have died from cancer (HR 1.32, 95% CI 1.18 to 1.48).
Lung cancer and cancers related to smoking were not linked to mental distress, once the researchers had adjusted for the effect of smoking.
How did the researchers interpret the results?
The researchers say their findings 'could be important in advancing understanding of the role of psychological distress in cancer aetiology (causation) and cancer progression'. They say the results show that psychological distress predicts the chances of death from certain types of cancer, but that this doesn't mean anxiety or depression are direct causes of cancer.
They also say that the 'sensitivity' of mental distress as a predictor of death from cancer is low, compared to smoking or obesity. However, they say, psychological distress could be considered as one risk factor to take account of when looking at someone's risk of getting or surviving a particular cancer.
Studies like this can be distressing for people with mental health difficulties and their families and friends. It's important to point out that having anxiety or depression, which are common illnesses, does not mean you will go on to get, or die from, cancer. It may be your risk of it higher, but cancer risk is complex. It includes many factors such as our genes, our environment and our lifestyle.
We don't know from the study whether mental distress is a cause of cancer, or of cancer mortality. It could be a reflection of another confounding factor – for example, people with poor mental health may have a poor diet, and diet is linked to cancer. Or mental distress could be a result of poor physical health, which itself could have increased the chances of death from cancer.
Even if mental distress is causally related to cancer, this could be for many reasons. Theories of a direct effect of mental health on cancer include the effect of stress on hormones and our immune system, which usually protects us against cancer. But behavioural factors, such as whether or not we attend cancer screening, show that mental ill health could have an indirect effect on our chances of surviving cancer.
Regardless of the link to cancer, anxiety and depression are serious illnesses that cause a great deal of distress. Treatments, including talking therapies and medicines are available and help many people. Getting help for mental health problems is worthwhile in itself, whether or not treatment could later affect your chances of cancer.
Read more about depression and low mood and how to get help.
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