Introduction: Several studies have argued a causal relationship between diabetes and depression, while others have highlighted that their association is a result of common risk factors. Because Mexico is a country with a high prevalence of diabetes, and diabetes and depression are a frequent comorbidity, we chose this country to investigate the longitudinal relationship of these two conditions, focusing on the influence of demographic, health, and socioeconomic factors which could act as common risk factors for both conditions.
Research design and methods: Using the harmonized Mexican Health and Aging Study, a nationally representative sample of adults older than 50 with a response rate of 93%, we analyzed the longitudinal relationship of diabetes and depressive symptoms using 'between-within' random-effects models, focusing on the effect of demographic, socioeconomic and health factors.
Results: While older adults with diabetes reported a higher prevalence of depressive symptoms in the four waves of the study, there was no causal longitudinal association between them once controlling for demographic, socioeconomic and health factors (between-effect OR=0.88, 95% CI 0.77 to 1.01; within-effect OR=0.87, 95% CI 0.69 to 1.11).
Conclusions: There is no causal longitudinal association between diabetes and depression; the higher prevalence of depression among older adults with diabetes seems a result of socioeconomic and health factors that are not exclusive to respondents with diabetes but are more frequent in this group. Our results highlight the importance of prevention and control of chronic conditions as well as the role of socioeconomic inequalities in mental health.
Keywords: aging; depression; diabetes mellitus; longitudinal studies; type 2.
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