Comorbidities: Meaning and Common Examples

Comorbidities are distinct health conditions that are present at the same time. They may exist together for many reasons, including shared causes and risk factors.

Comorbidities can increase your risk of complications or developing a new health issue altogether. Being aware of possible comorbidities and how conditions interact can help your healthcare provider ensure you get the best possible care.

This article looks at the causes of comorbidities, provides examples of different types, and explains why it's important to understand them for diagnosis, treatment, and prevention of disease.

Causes of Comorbidities

Comorbidities can exist in many different combinations. It is also possible to have more than one comorbidity at the same time.

Conditions described as comorbidities can be physical or mental in nature. They're typically chronic (long-term) concerns.

There are a few different reasons conditions can exist side-by-side:

• They share the same cause(s) or risk factors.
• One causes the other.
• They're not related at all (just coincidence).

Shared Risk Factors or Causes

Some illnesses share an underlying cause or risk factors that increase your odds of developing them.

Shared Risk Factors

Many serious and common comorbidities occur because of shared risk factors.

Example: Stroke and heart attack

A stroke happens when the flow of blood and oxygen to the brain is interrupted. A heart attack happens when an artery is blocked and can't deliver blood and oxygen to the heart. They're different, but they both involve problems with moving blood through your body.

These medical events share risk factors including:

• High blood pressure
• High "bad" cholesterol (LDL) levels
• Diabetes
• Smoking or secondhand smoke exposure
• Obesity
• Unhealthy diet
• Lack of physical activity
  

Because these risk factors make both stroke and heart attack more likely, some people may have both. In fact, the risk of a stroke is higher in the year following a heart attack.

Shared Causes

Many conditions are believed to have the same underlying cause.

Example: Lupus and rheumatoid arthritis

Both of these conditions are autoimmune. That means the immune system mistakenly attacks healthy parts of your body as if they were disease-causing viruses or bacteria.

Because they involve the same process—just with different targets of the immune system—having one autoimmune disease means you're at risk for another, or even several more.

Example: Fibromyalgia and irritable bowel syndrome (IBS)

Fibromyalgia is a common chronic pain disease that involves fatigue, pain, and cognitive dysfunction. IBS is a digestive disorder. So they may seem quite different.

But experts suspect fibromyalgia and IBS both involve something called central sensitization. That means the central nervous system is hypersensitized and easy to irritate.

When sensitization affects the nerves, pain processing, and certain hormones/brain chemicals, it manifests as fibromyalgia. When those things affect the digestive organs, it manifests as IBS.

These conditions and other central sensitivity syndromes (CSS) are common comorbidities. Other CSS include:

• Migraine
• ME/CFS (myalgic encephalomyelitis/chronic fatigue syndrome)
• TMJ (temporomandibular joint disorder)
  
• Multiple chemical sensitivity
• Restless legs syndrome

Many people have several of these comorbidities due to their common underlying mechanisms.

One Condition Causes the Other

Sometimes, one condition directly causes the other.

Example: High blood pressure (hypertension) and heart disease

A common cause-and-effect comorbidity is high blood pressure and heart disease. They're two different diagnoses, but hypertension can lead directly to heart disease by damaging your arteries.

Example: Depression and chronic illness

Depression is comorbid with most chronic illnesses. In some cases, that may be partly due to common physiology, such as brain-chemical (neurotransmitter) abnormalities. However, it's also due to the symptoms and stresses of living with a chronic illness.

Example: Obesity and many conditions

A condition that can directly lead to numerous and varied comorbidities is obesity. It's tied to approximately 236 medical problems. Common ones include:

• Type 2 diabetes
• High blood pressure
• Dyslipidemia (high blood lipid levels including high cholesterol)
• Cardiovascular disease
• Stroke
• Sleep apnea
• Gallbladder disease
• Hyperuricemia (excess levels of uric acid in the blood, a risk factor for gout)
• Osteoarthritis
• Breast, colorectal, gallbladder, and other cancers

Obesity is thought to be comorbid with these conditions because:

• Excess weight can put physical stress on the joints, leading to problems like osteoarthritis.
• Excess weight can push on the chest and diaphragm and cause the soft tissues of the throat to collapse, leading to sleep apnea.
• An increase in hormones and other substances secreted by adipose (fat) tissue impacts the endocrine (hormone) system, resulting in diabetes and other metabolic conditions.
• Physical and metabolic problems can harm the body's organs, such as the heart and kidneys.

The Role of Symptoms and Treatments in Comorbidity

Sometimes, the symptoms of one illness can make you more likely to develop another.

Example: Mental health and substance use disorder

Anxiety and depression can lead someone to abuse drugs or alcohol in an attempt to feel better, which can lead to substance use disorder (addiction).

It's also possible for a medication you take for one condition to cause a comorbidity.

Example: Hyponatremia

Hyponatremia is a condition involving abnormally low levels of sodium in your blood. It can be caused by:

• Antidepressants
• Anti-anxiety drugs
• Chemotherapy
  

Coincidence

Coincidence is just two things happening that have nothing to do with each other. For example, you may have a peanut allergy and a genetic eye disease that are unrelated.

Also, comorbidities that sometimes have a cause and effect relationship may at other times be coincidental.

Example: Diabetes and heart disease

Diabetes is a well-recognized cause of heart disease. Excess blood sugar over time damages blood vessels and can lead to heart attack and stroke. But the two conditions may also be coincidental: If your diabetes is well controlled and you don't have damaged blood vessels, you may have a heart attack for an unrelated reason (such as a birth defect in your heart.)

This can also be the case when you get them in the reverse order, such as having a heart attack before developing diabetes. In that case, one may not cause the other and it's just a coincidence that you have both.

Why Recognizing Comorbidities Is Important

It's important to recognize and understand comorbidities for several reasons, including disease prevention and issues with diagnosis and treatment.

Disease Prevention

If you have a diagnosis that can lead to comorbidities, you may be able to take steps to prevent those other conditions from developing.

Example: Hypertension

Say you're diagnosed with hypertension. Your healthcare provider will likely advise you to improve your diet and fitness level, and potentially take medications, to lower your risk of comorbidities such as heart attack and stroke.

Acute Conditions and Comorbidities

While comorbidities are usually chronic conditions, sometimes it's important to recognize how some of them affect acute (short-term) infectious illnesses. Having one condition may mean you need to take extra precautions to prevent an infection.

Example: COVID-19

You're more likely to have a serious or fatal case of COVID-19 if you also have:

• Cancer
• Chronic lung or kidney disease
• High blood pressure
• Obesity
• HIV/AIDS
• Diabetes

Example: Influenza

The flu (influenza) also poses extra risks for people with many chronic illnesses, including:

• Asthma
• Chronic heart or lung disease
• Blood disorders
• A weakened immune system

In cases like this, it's important for people with chronic diagnoses to take extra steps to prevent a comorbid acute illness or receive prompt treatment for it.

Diagnosis

Understanding comorbidities can also help with the diagnostic process by giving your healthcare provider a place to start.

Example: Autoimmune diseases

Say you have an autoimmune disease that affects your eyes and you develop joint pain. It may make more sense for your healthcare provider to first consider autoimmune pain conditions, such as lupus or rheumatoid arthritis, rather than non-autoimmune diseases like osteoarthritis and gout.

Recognizing comorbidities can also help your healthcare provider properly diagnose and treat all of your conditions, which gives you a better chance of feeling and functioning well.

Example: Fibromyalgia and digestive symptoms

Fibromyalgia can involve some digestive symptoms, but if someone's digestive symptoms get worse while other fibromyalgia symptoms are stable, it could mean they've developed IBS—which may require different treatments.

Treatment

When you have comorbidities, it can complicate treatment and management. Your healthcare team may monitor you more closely, as well.

In general, outcomes tend to be worse for people with comorbidities than for those with only one diagnosis. Close medical oversight can help improve outcomes.

Medication Considerations

When prescribing medications, your healthcare provider needs to consider all of your diagnoses and everything else you take. That includes prescription and over-the-counter (OTC) drugs and nutritional supplements.

This is important because:

• Some medications may increase symptoms of a comorbid disease or interact badly with medications for that disease.
• Certain drugs for one condition may be off-limits to you because of your comorbidities or other treatments.
• Combining some medications can also increase your risk of unpleasant side effects.

Depending on your mix of diagnoses, possible comorbidities, and treatments, you may need medical tests to make sure nothing is having unintended effects.

Example: Liver disease and medications

If you have liver disease or a condition that could cause comorbid liver disease, your provider may be extra cautious about giving you medications that can harm the liver. If you take one, they may regularly test your liver enzymes so they can take action at the first signs of a problem.

Make sure every healthcare provider you see has a full, updated list of your medications and diagnoses. This is the first step toward avoiding problems.

When it comes to combining medications, it's important to stick to one pharmacy as much as possible. Then your pharmacist can fulfill their intended role, which is to watch for potentially dangerous drug interactions.

Consultation and Collaboration

The more comorbidities you have and the more medications you take, the more complicated the situation becomes. Your healthcare providers may need to consult with each other from time to time or regularly collaborate on your treatments.

It's a good idea for you to be proactive about your treatment. If one healthcare provider prescribes a new treatment or makes a new diagnosis, you may want to check in with your other providers about how it may affect things.

Summary

Comorbidity means you have more than one illness at once. It has many causes.

Some conditions have common underlying causes or risk factors, while some comorbidities are directly caused by another condition, its symptoms, or its treatments. Sometimes, conditions are comorbid by coincidence.

Comorbidities are important for disease prevention, diagnosis, and treatment. Comorbid conditions may complicate each other or affect treatment and management strategies.

All of your healthcare providers need to know about all of your comorbidities and treatments.

A Word From Verywell

Comorbidities can be challenging to live with. You may need to see a few different types of healthcare providers before you can put together the right comprehensive treatment plan for you.

Being proactive, working closely with your healthcare providers, and putting together a strong healthcare team can help you feel better and be more functional.