Comorbidities are more than one disorder in the same person. For example, if a person is diagnosed with both social anxiety disorder (SAD) and major depressive disorder (MDD), they are said to have comorbid (meaning co-existing) anxiety and depressive disorders.

Other comorbid conditions include physical ailments such as diabetes, cardiovascular disease, cancer, infectious diseases, and dementia. Mental health conditions that tend to show comorbidity include eating disorders, anxiety disorders, and substance abuse.

The term comorbidity was coined in the 1970s by A.R. Feinstein, a renowned American doctor and epidemiologist. Feinstein demonstrated comorbidity through the example of how people with rheumatic fever also usually suffered from multiple other diseases. Since that time, comorbidity has come to be associated with the presence of multiple mental or physical health conditions in the same person.

Prevalence of Comorbidities

It’s not uncommon for people to be diagnosed with two disorders or conditions at once. Comorbidity in mental illness can include a situation where a person receives a medical diagnosis that is followed by the diagnosis of a mental disorder (or vice versa), or it can involve the diagnosis of a mental disorder that is followed by the diagnosis of another mental disorder.

A large, cross-sectional, national epidemiological study of comorbid conditions in mental health in Spain showed that among a sample of 7936 adult patients, about half had more than one psychiatric disorder. Furthermore, in the U.S. National Comorbidity Survey, 51% of patients with a diagnosis of major depression also had at least one anxiety disorder. Only 26% of them had no other mental health condition.

In the Early Developmental Stages of Psychopathology Study, 48.6% of patients with a diagnosis of major depression also had at least one anxiety disorder. Just over one-third (34.8%) had no other mental disorder.


Can Comorbidities Be Prevented?

Healthcare professionals can play a role in preventing comorbidity. For example, if a social anxiety disorder is left untreated for a long period of time, a person may also develop depression and/or substance abuse in response to the anxiety symptoms. So prompt diagnosis and treatment of one condition may prevent the development of comorbidities.

At a broader level, coordination between primary doctors and mental health professionals is key to preventing comorbid conditions. If you’ve been diagnosed with a physical and/or mental health condition, keep good records of the care that you receive from various professionals, so that each can be aware of the various treatments you are receiving.

Mental Illness Linked to Chronic Physical Illnesses

Depression, generalized anxiety disorder, and schizophrenia affect about 6% of the world’s population, taking only documented cases into account. In low- and middle-income countries, about eight of ten people who have severe mental illness cannot get care for it. Probably, for this reason, mental disorders are the second highest cause of sickness and death in these countries.

Mental disorders are often linked to one or more chronic physical disorders and can exacerbate their physical impact on the patient. A second issue with mental conditions occurring in people with physical illness is that the latter are less well treated than they would be in mentally sound people.

Among fatal chronic physical illnesses leading to death, cardiovascular disease accounted for almost a third, cancers for one in seven, and chronic lung disease contributed 7%. Diabetes and other chronic conditions caused over a tenth of the remaining.


Physical Illness Linked to Mental Illness

People with certain of these chronic physical illnesses (cancer, obesity, diabetes, chronic obstructive pulmonary disease (COPD), and cardiovascular disease) have a higher prevalence of mental disorders. Depression is found to be present in 13-80% of chronically ill patients. This, along with other mental disorders, is more prevalent in hospitalized patients, and they are also more severe in this subgroup.

COPD is linked to mental illness, with almost three-quarters of individuals with severe COPD showing features of anxiety and depression. Smoking, which is a common practice among psychiatric patients, is linked to COPD. Smoking not only helps relieve mental stress and is likely to be more common among the poor, those without secure housing, unemployed, or feel socially excluded.

Conversely, several studies reported an association between mental comorbidities and chronic physical conditions in anywhere from ~20-70% of cases. A large meta-analysis showed that four mental disorders, namely, anxiety, depression, bipolar disorders, and schizophrenia, are linked to as much as two out of three chronic physical disorders.

The presence of mental disorders increases the risk of chronic physical illnesses like obesity or diabetes. Up to one in seven people with schizophrenia or bipolar disorder (BPD) have been reported to have obesity with/or diabetes. In the case of depression, it is closer to one in five.

Other researchers have reported diabetes in over a fourth of people with BPD, while obesity has been reported in over 40% of schizophrenic patients. Diabetes is thus found to be 4-5 times more prevalent in people with schizophrenia, and 3 times higher among those with BPD, than in the general population.

Depression is found to co-exist with chronic illness in 17% of those with cardiovascular disease, just under a quarter of those with stroke, and 27% of those with diabetes.

Mental health issues prevent proper self-care in COPD, increasing symptomatology and causing a higher hospitalization rate, with higher costs and reduced quality of life. Similarly, arthritis rates may be higher among those with mental illness.

Certain cancers are found to be higher among people with schizophrenia, especially gallbladder and bowel cancers. Cancers can precipitate stress, emotional upset, and a poor body image. More than 40% of people with cancer also have depression.


Mental Health is Just as Important as Physical Health

Mental comorbidities in people with chronic physical illness pose a formidable challenge for healthcare management in low- and middle-income countries. With poor access to mental health services, this deserves to be put on the front burner in these countries. As some experts say, there is “No health without mental health.”

Many measures can be taken to prevent or treat such coexisting illnesses. This includes addressing modifiable risks like tobacco use, physical inactivity, and unhealthy eating habits that cause or contribute to both mental and physical poor health.

Workplace practices that promote poor mental health, such as high job demands, lack of control over the job conditions, scheduling issues, and physical exertion or sedentary conditions, also need to be addressed. An example is the Copenhagen Healthy Bus Program that used multidimensional interventions to successfully mitigate both chronic illness and mental illness risk among bus drivers in the city of Copenhagen, over its five-year course.

Not only did work schedules, communication within the workforce, and management practices improve, but smoking cessation program use, dietary habits, and exercise frequency all improved significantly among the drivers, which could drive better health and a lower risk of chronic disease and mental ill-health. Routine healthcare services, at all levels, must include a right awareness of mental health problems, allowing for planning and integration of services for this sector.