Approximately 3.8% of the world’s population is impacted by depression, making it one of the most common health conditions individuals may face in their lifetime. The most widely recognized symptom of depression is a low mood, but individuals with this disorder also contend with an inability to feel joy, disrupted sleep and eating patterns, loss of interest in previously pleasurable activities, fatigue, and trouble thinking clearly. These symptoms can impair their ability to work, care for themselves, and engage in relationships and social activities.
20% of individuals with chronic physical conditions also develop depression. One of the most widely seen combinations is co-occurring anxiety and depression, with 60% of individuals with one of the disorders having symptoms of the other. For individuals with depression, the risk of having a comorbid chronic physical health condition is significant at 72%. No matter what the combination, medication interactions become a concern when addressing multiple symptoms and coordinating treatments.
Read on to review how depression and co-occurring disorders develop and impact each other, including several cardiovascular conditions, dementia, chronic pain, and human immunodeficiency virus (HIV).
Before we continue, a note on comorbidity vs. causality. Depression often develops in comorbidity with other disorders. However, comorbidity is not the same as causality: two or more disorders may have similar risk factors, or they may overlap each other in timing but have different identifiable causes. Comorbid disorders may also develop because coping with one can make all aspects of an individual’s health more vulnerable. But their co-occurrence may not mean one disorder directly caused the other to develop.
Cardiovascular disease (CVD) is the leading cause of death worldwide. This broad category includes several of the most common co-occurring disorders with depression. It has close ties with depression, occurring for 25% of all CVD patients. Depression interacts differently with each type of CVD condition, with some of the most prevalent reviewed here.
A stroke occurs when a blood clot becomes loose in the bloodstream and blocks the flow of blood in the brain. This can quickly cut off the oxygen and supply to brain cells, leading to cell damage and sometimes death.
Approximately 2.7% of the United States population is at risk for stroke, with 21% of those individuals also developing depression. The brain damage caused by a stroke can significantly impair an individual’s ability to talk, walk, and live independently. Even with therapy and recovery, these limitations can be discouraging and feel like a tremendous loss.
Hypertension, also known as high blood pressure, affects nearly half of all adults in the United States. When blood vessel walls become thicker and less flexible, the pressure increases as the heart works harder to pump blood. Hypertension eventually damages the heart and can be caused by too much dietary sodium, high cholesterol levels, smoking, obesity, and genetic risk.
About 21% of those with hypertension also have depression, with the risk going in both directions. Depression can lead to unhealthy behaviors that contribute to the risk of hypertension, such as poor sleep, overeating that leads to weight gain, substance misuse, and a sedentary lifestyle. And some medications used to treat depression, particularly serotonin-norepinephrine reuptake inhibitors (SNRIs), can elevate blood pressure.
Heart failure occurs when the heart gradually loses the ability to pump enough blood to meet the body’s needs. The heart’s poor functioning means blood and other fluid may pool in the veins and other parts of the body, a type of heart failure called congestive heart failure. 6.2 million adults in the United States have some form of heart failure, with symptoms including shortness of breath, fatigue, weight gain, and swelling in the feet and ankles.
The co-occurrence of heart failure and depression is linked to increased mortality. Poor self-care, a sedentary lifestyle, and not following diet recommendations are linked with worse outcomes. Inflammation is linked with both depression and the pathology of some forms of heart failure, indicating a potential physiological connection between the two conditions.
Coronary artery disease (CAD) is the most common type of cardiovascular disease, affecting 6.6% of adults in the United States. It refers to the buildup of plaque in the walls of the heart’s arteries. If left untreated, this buildup can gradually limit blood flow to the heart muscle, eventually leading to a near or complete blockage and possibly a heart attack. Narrowing of the arteries can also occur due to sudden breakage of plaque or the formation of a blood clot.
Remarkably, the associations are so strong between both conditions that an otherwise medically healthy individual with depression may be more likely to die from a cardiac condition such as CAD than those without depression. Some evidence suggests that the co-occurrence of depression and coronary arises from shared environmental and genetic factors. This may include maltreatment in childhood and factors affecting fetal growth during pregnancy. Studies also show that specific immune system cells and a type of fat in the blood associated with CAD may be linked causally to the development of depression. However, the etiology behind these connections is unclear.
Dementia is a loss of cognitive functioning, the skills individuals use to think, make decisions, and remember. These changes can impact relationships, independent living skills, and emotional wellbeing, significantly diminishing an individual’s quality of life. Understandably, 32% of individuals with dementia also develop depressive disorders, which can contribute to poor cognitive functioning. Also, research suggests that progressive depression symptoms in late life may increase the risk of dementia.
Because aging adults are more likely to develop health conditions requiring medication treatments, individuals with dementia and depression are at a higher risk for drug interactions and may be less sensitive to the effects of antidepressants.
Chronic pain can develop and persist for many reasons, often as a symptom of a persistent medical condition. An estimated 20.4% of adults in the United States live with chronic pain, and 8% cope with high-impact chronic pain, a more severe and disruptive type of pain. Because of the distress caused by chronic pain, 31% of individuals with this condition also develop depression.
Research has also examined how both conditions impact the brain’s neuroplasticity, its ability to adapt to stimuli and change, such as a brain injury or learning a new skill. Studies have shown that depression and chronic pain affect neuroplasticity in similar ways. This may lead to a more frequent co-occurrence of both conditions.
Human immunodeficiency virus (HIV) causes an infection that attacks the white blood cells in the immune system, making individuals more vulnerable to infectious illnesses. If left untreated, HIV infection can develop into acquired immunodeficiency syndrome (AIDS), the most advanced stage of damage to an individual’s immune system.
In 2020, 37.7 million people were living with HIV infection. One study indicates that individuals living with HIV infection have a higher rate of co-occurring depression than any other health condition at 41%. The elevated risk for depression may stem from the occurrence of HIV infection among vulnerable individuals concerned for others struggling with the condition, dwelling on their own health risks, and coping with HIV treatment setbacks.
Given its high prevalence, it is unsurprising that so many medical conditions co-occur with depression. When addressing co-occurring health conditions, care must be taken to ensure individuals get accurate diagnoses and safe, effective treatment options.