Study: Depression Causing Physical Illness, Not The Other Way Round
New Australian research has found depression causes up to 20 distinct diseases, including heart disease and high cholesterol -- findings that reverse common perceptions around physical and mental illness.
A study led by researchers from the Australian Centre for Precision Health used genetic data to asses the risk factors between major depressive disorder (MDD) and 925 other diseases.
It found a causal link between MDD and a range of respiratory, heart and digestive diseases, including a 30 percent increased risk of coronary heart disease and a 20 percent increased risk of asthma.
While some of the associations were already known from clinical practice, lead author, Professor Elina Hypponen, said the study is the first to show a causal link using a genetic approach.
"With this approach, we only picked up diseases that are affected by depression, rather than the other way around," Hypponen told 10 daily.
"Our work very much highlighted that depression in itself can increase the risk of other diseases."
Along with heart disease and high cholesterol, researchers observed associations between depression and inflammatory and bleeding-related diseases of the gastrointestinal and urinary systems.
Hypponen said findings relating to an increased risk of anxiety and sleep disorders were less surprising.
Approximately three million Australians are living with anxiety or depression, according to Beyond Blue.
Depression, among other mental illnesses, can affect all aspects of a person's life, but evidence relating to the causal effects on health is limited, according to the researchers.
Recent data from the Australian Institute of Health and Welfare shows those living with serious mental diseases have much higher rates of physical illness than those who don't.
Last year, an Australian-led study from the NICM Health Research Institute found a two-decade gap in life expectancy between people with mental illness and the general population.
At the time, Doctor Joseph Firth, a senior research fellow at NICM Health Research Institute and lead author, described the disparity in physical health outcomes for people with mental illness as a "human rights scandal".
But Hypponen said it can often be difficult to know "what causes what".
Co-author and University of South Australia researcher, Anwar Mulugeta, said studies have often been complicated by the possibility of other confounding factors -- or "reverse causation", where the physical condition is assumed to cause depression.
“This research puts the ‘chicken and egg’ conundrum to rest, showing that depression causes disease, rather than only the other way around," Mulugeta said.
Importantly, Hypponen said many of the diseases that were found to be linked to depression can be prevented.
"When it comes to heart disease, for example, it simply reminds us that even in the context of depression, it is important to try and maintain a healthy diet," she said.
With the increased risk of diseases characterised by inflammation of the gastrointestinal and urinary systems, researchers want to see those individuals who are using anti-depressant medications monitored for possible side effects.
They are also calling on patients who are diagnosed with depression to be screened for a defined set of other diseases.
Ultimately, Hypponen said the research adds to a growing chorus for a more more holistic approach to treating mental illness.
"I think we are moving towards a very different future," she said.
"I think the more the approach to health becomes holistic -- capable of considering all of the conditions along with the lifestyle of an individual -- the better outcomes we will probably be seeing."
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