A comorbidity refers to having two or more conditions or diseases at the same time in a person, such as a person with both diabetes and liver disease. Comorbid conditions are typically associated with more severe disease and more complex care. They are often, but not always, related, such as sharing underlying causes or risk factors or one causing or worsening the other. Common conditions that often co-occur with other conditions include arthritis, asthma, chronic pain, cancer, diabetes, cardiovascular disease, hepatitis and mental health conditions.
Deeper dive
Comorbidities may coexist because they are related to one another (one causes the other or they both result from a shared underlying factor) or because of coincidence. In a person with an anxiety disorder and severe tooth decay, the conditions are most likely not related. But sometimes conditions can have unexpected links.
A person with obsessive compulsive disorder, a type of anxiety issue, may develop severe dental problems if their OCD leads to excessive teeth-brushing that damages their enamel. Other times, the conditions may not be directly related, but one can exacerbate another. A person might have cirrhosis of the liver and major depressive disorder at the same time that were not initially related, but reduced quality of life from cirrhosis might worsen depression symptoms.
Comorbidities typically refer to chronic conditions, but a person may have an acute condition along with chronic comorbidities. Most often, the comorbid conditions are related because they share risk factors or affect the same body systems, or because one increases the risk of the other.
Certain mental health disorders often co-occur with substance use disorders in those who self-medicate and/or did not receive appropriate treatment for their mental disorder. Diabetes is a risk factor for cardiovascular disease and often occurs with a comorbidity of atherosclerosis.
Unsurprisingly, comorbidities increase with age. Comorbid conditions are also associated with more severe disease and more complex care and treatment needs. Some of the most common conditions that involve comorbidities are arthritis, asthma, chronic pain, hepatitis, dementia, back problems, cancer, diabetes, cardiovascular disease, mental health conditions, autoimmune conditions and chronic obstructive pulmonary disease.
In covering medical studies, understanding comorbidities becomes especially important because the presence or absence of certain comorbidities may influence study findings, especially if the researchers don’t control for them. If researchers were to conduct a study on risk factors for cardiovascular disease, and they did not account for participants with high cholesterol, diabetes, obesity, smoking, or other comorbidities, the results would not be valid. Looking at what comorbidities a study does or doesn’t account for may be a place reporters find significant limitations in a study, or at least questions to ask the researchers.