T2DM and MDD frequently coexist; however, the underlying mechanisms for this comorbidity remain unclear (Clarke, 2017). The prevalence of depression within the diabetic population is notably high, with the majority of patients experiencing minimal depressive symptoms, while approximately 20-30% present with mild to moderate depression (Khan, 2019; Ali, 2006, Woon 2020). Additionally, co-morbid depression significantly increased the odds of developing anxiety, with an adjusted odds ratio (OR) of 9.89 (95% confidence interval [CI] = 2.63–37.14, p = 0.001) (Woon 2020). The presence of diabetes is associated with a twofold increase in the likelihood of comorbid depression (odds ratio = 2.0, 95% confidence interval 1.8-2.2) (Anderson, 2001). Emerging evidence indicates a bidirectional relationship between diabetes and mental health disorders, suggesting that these conditions can exacerbate one another. One study found that individuals with more severe psychiatric symptoms exhibited poorer diabetes control, whereas those with lower levels of psychiatric symptoms demonstrated better diabetes management (Gunzler, 2017).

Does Emotional Stress Contribute to the Onset of T2DM?

Significant diabetes-specific emotional issues are particularly prevalent among depressed patients with diabetes (Pouwer, 2005). Stress is typically understood as the result of an organism's failure to respond appropriately to actual or perceived emotional or physical threats (Bao, 2008). This raises the question of whether emotional stress contributes to the onset of Type 2 Diabetes Mellitus (T2DM). Research findings indicate that various forms of emotional stress—particularly depression, general stress, anxiety, anger, and sleep disturbances—are linked to an increased risk of developing T2DM. Currently, the clinical implications of these findings are limited, necessitating more rigorous research to establish a causal relationship between stress and the onset of depression (Pouwer, 2010).

Risk factor and Protective factors of co-morbid depression in T2DM

Researchers reported main influencing factors of co-morbid depression among T2DM from a systematic review and meta-analysis. The result found there were 3 main risk factors and 4 main protective factors of co-morbid depression in type 2 DM (Simayi 2019).

Risk factor of co-morbid depression in T2DM

1. Diabetic complications (OR = 2.91; 95%CI, 1.76–4.82, p < 0.0001)

2. Insulin use (OR = 1.71; 95%CI, 1.18–2.48, p = 0.005)

3. Education status less than secondary school (OR = 1.91; 95%CI, 1.30–2.81, p = 0.001)

Protective factors of co-morbid depression in type 2 DM

1. Regular exercise (OR = 0.51; 95%CI, 0.27–0.96, p = 0.04)

2. Gender - male (OR = 0.56; 95%CI, 0.47–0.65, p < 0.0001)

3. Marital status - being married (OR = 0.53; 95%CI, 0.34–0.83, p = 0.005)

4. Current social status - on work (OR = 0.64; 95%CI, 0.47–0.88, p = 0.006)

A Newer Alternative Treatment of co-morbid depression in T2DM

A systematic review and meta-analysis assessed depression treatments in patients with diabetes and comorbid major depressive disorder (MDD) or subthreshold symptoms. The study found that all interventions—pharmacotherapy, psychotherapy, collaborative care, online and phone support, group interventions, and exercise—significantly improved depression outcomes compared to usual care, placebo, or waiting lists (van der Feltz-Cornelis 2020). Additionally, pharmacological treatment, group therapy, psychotherapy, and collaborative care positively affected glycemic control (van der Feltz-Cornelis 2020). Primary treatments for diabetes and depression in primary care primarily involve oral hypoglycemic agents and antidepressants. However, patients with both conditions often experience inadequate management due to overestimated adherence to medication (Bogner, 2013). While effective treatments exist for both diabetes and mental health issues, separate service delivery overlooks their interrelatedness, resulting in inefficiencies (Harkness, 2010) comorbidities and poor outcome (Huang 2013). The author proposes alternative treatment programs beyond pharmacological treatment and cognitive behavioral therapy (CBT), such as collaborative care (Huang, 2013) and eHealth-based interventions (Varela, 2022), to enhance outcomes for medical professionals.

Collaborative care 

Collaborative care represents a coordinated management model involving primary care physicians, nurses, and other specialists, focusing on patient-oriented, guideline-based treatment at the primary care level (Archer, 2012). This complex intervention is rooted in the chronic care model and includes various organizational, professional, and patient-level strategies. It entails mental health interventions conducted by a patient's general practitioner alongside at least one other health professional—such as a nurse, psychologist, psychiatrist, or pharmacist—emphasizing scheduled follow-ups and enhanced inter-professional communication within the care team (Coventry, 2012). In diabetic patients, a study by Huang (2013) demonstrated that collaborative care significantly improved depression outcomes, as well as adherence to both antidepressant medication and oral hypoglycemic agents. The findings indicated that collaborative care enhanced the treatment response for depression and was significantly associated with higher adherence rates to antidepressant medication (RR = 1.79, 95% CI = 1.19-2.69) and oral hypoglycemic agents (RR = 2.18, 95% CI = 1.61-2.96) among depressed patients with diabetes.

eHealth-based psychological interventions for depression treatment

Depressive symptoms can impact glycemic control, largely through indirect effects on self-care behaviors (Snoek et al., 2015). Although effective treatments for depression exist, resources are limited, leaving 50% of patients untreated (Egede and Ellis, 2010). Due to the high cost of face-to-face treatment, pharmacological options are often preferred. eHealth programs, using ICT-based (Information and Communications Technology-based) non-face-to-face interventions like cognitive behavioral therapy (CBT), psychoeducation, and self-care management such as diet-related thoughts, physical activity, and medication management, have emerged as alternatives. A systematic review by Varela-Moreno (2022) found that eHealth interventions improved depressive symptoms in diabetes patients in both the short (3 months) and long term (6–12 months) but showed minimal impact on glycemic control.

Conclusion

Depression commonly coexists with diabetes, affecting about 20-30% of patients with mild to moderate symptoms. The main risk factors for co-morbid depression in type 2 diabetes include diabetic complications, insulin use, and education below secondary level. Due to the high cost of in-person treatment, pharmacological options are often preferred. However, alternative treatments like collaborative care and eHealth-based psychological interventions can also help improve depression in diabetes.