How Does Major Depressive Disorder Affect Other Conditions in Patients?

Major depressive disorder (MDD), a condition whose definition includes a persistently low mood, lack of energy, and feelings of worthlessness, is projected to be the leading cause of worldwide disease burden by 2030.¹ Patients with MDD may also experience anhedonia, difficulty concentrating, and changes in appetite.

According to statistics from the National Institute of Mental Health, in 2021, 8.3% of adults in the US had at least one major depressive episode.² This included 18.6% of Americans aged 18 to 25 and 9.3% aged 26 to 49. In adolescents, the rate was 20.1%, with 29.2% of female adolescents reporting a major depressive episode. Given the prevalence of MDD and projected increases, it is important to understand the various ways this condition affects patients.

Major depressive disorder is often associated with a number of comorbidities and can play a role in the progression and disease burden of other disorders. What do we know about how MDD affects certain comorbidities and how it affects the risk for other conditions?

MDD and Cancers

Different studies have come to varying conclusions regarding whether MDD is linked to increased risk for cancer. A 2023 study published in Brain Sciences, for example, used data from over 235,000 patients and suggested that patients with depression can have a 10 to 39% increase in risk depending on the type of cancer.³ The researchers found the risk in these patients was highest for lung, breast, urinary, and gastrointestinal cancers.

However, a different 2023 study, this one published in Cancer, used data from 18 additional studies to conclude that depression and anxiety were not associated with an increased risk for most cancer outcomes.⁴ The researchers did acknowledge an increased lung cancer risk, but found it significantly reduced after adjusting for risk factors like smoking.

While studies differ on whether depression increases cancer risk, studies focused on outcomes for patients who already have cancer have suggested that there may be a link for certain cancers. In a recent study in the Journal of the National Cancer Institute, researchers used data from over 6,000 women with breast cancer to suggest that MDD was associated with worse breast cancer outcomes.⁵ This included MDD being associated with recurrence, particularly in women with estrogen receptor-positive breast cancer, and breast cancer mortality.

Interventions that focus on depression can potentially have a beneficial effect on cancer patients. Researchers at the University of Arizona Cancer Center ran a 12-week depression program for a diverse group of patients with cancer and found that across ethnicity, education, income, and stage of cancer, patients in the program experienced a significant improvement in their quality of life.⁶

MDD and Diabetes

MDD and depressive symptoms are associated with increased risk of diabetes, as well as elevated glycated hemoglobin levels and impaired self-management.⁷ Some reviews, like a 2022 one in the Journal of Clinical Psychology, found that MDD was associated with a particularly increased incidence of diabetes in men, and an overall increase in worsening diabetes symptoms.⁸

Patients with diabetes may also be at risk of specific complications worsening with MDD. Researchers of a 2024 study in eClinicalMedicine concluded that MDD may play a role in the development of vascular complications in patients with diabetes, and that further investigation is needed.⁹

MDD and Cardiovascular Disorders

Major depressive disorder can be a significant risk factor for both the incidence of cardiovascular diseases and the worsening of effects in existing cardiovascular disease.⁸

This may be due in part to additional risk factors that are associated with MDD. A study in the Journal of the American Heart Association found potential evidence of a causal link between MDD and peripheral artery disease, citing the link between MDD, lifetime smoking, and increased body mass index.¹⁰

MDD and Respiratory Disorders

The higher likelihood of smoking among patients with MDD may also play a role in the risk of developing or worsening respiratory disorders. Severity of depression has been associated with chronic obstructive pulmonary disease (COPD) and asthma incidence in the past, and recent studies have suggested similar findings. A review published in European Psychiatry in 2025 found patients with MDD to have significantly higher rates of COPD than those without MDD, as well as asthma.¹¹ The researchers found women and younger patients to be at an especially high risk of COPD, and that preventative measures are needed for those at risk. 

MDD and Psychiatric Disorders

How does major depressive disorder affect other comorbid mental health disorders? One key association is with substance use disorder; depression can be associated with an increase in drug use and severity of drug abuse.⁸

MDD is also frequently associated with generalized anxiety disorder (GAD), with some studies estimating as many as 50 to 75% of patients with MDD meeting the criteria for comorbid anxiety.¹² Patients with MDD and anxiety are more likely to have a decreased quality of life and worse psychosocial function. In addition, a 2022 study in the Journal of Psychiatric Research also suggested that MDD and comorbid GAD were associated with higher levels of inflammatory markers, as well as higher levels of neuroticism and stress.¹³

Another common mental health comorbidity in MDD is borderline personality disorder (BPD). One 2024 study in Frontiers in Psychiatry estimates that BPD is diagnosed in 10 to 30% of patients with MDD, and that over 80% of patients with BPD have an MDD diagnosis.¹⁴ These conditions comorbid with one another are linked to more severe depressive symptoms, increased suicidal ideation, and higher levels of treatment resistance.

All these comorbidities highlight the need for a more personalized MDD treatment for patients tailored not just to their depression, but to the way it affects the other comorbidities they have.

This article originally appeared on Psychiatry Advisor