Association between cognitive decline and depression in middle-aged and older adults: Findings from six large cohorts in different countries

BACKGROUND: The relationship between depression and cognition in middle-aged adults is a topic of interest. Whether poor cognitive function exacerbates depression remains controversial. We clarified the association between cognitive decline and depression based on six nationwide cohorts. METHODS: 89,056 participants were retrieved from six cohorts in Europe, North America, Asia and Africa. Each two consecutive interviews were collected as a sample set with a total of twenty-eight sample sets to assess changes in depression and cognitive function. Multiple linear regression was conducted within each sample set to evaluate the association between cognitive decline and depression. A two-stage meta-analysis was performed to obtain the average effect within each cohort and the overall effect excluding population and regional heterogeneity. Meta-regression and subgroup analysis were used to explore heterogeneity and potential effect modifiers. RESULTS: Almost all sample sets indicated negative association between changes in cognitive function and depression scores. The average effects varied across regions: Korea (-0.150 [-0.175, -0.126]), Europe (-0.130 [-0.149, -0.112]), South Africa (-0.090 [-0.129, -0.060]), China (-0.083 [-0.137, -0.030]), Mexico (-0.063 [-0.084, -0.042]), and North America (-0.048 [-0.056, -0.040]). The overall effect excluding population and regional heterogeneity was -0.094 [-0.129, -0.060], and was robust across populations of different age, sex, alcohol consumption, daily living activities and marital status. LIMITATIONS: The cross-sectional design limited our ability to determine causal relationships. CONCLUSION: Cognitive decline was associated with the exacerbation of depression status in middle-aged and older adults worldwide. Country-level factors, rather than individual-level factors, are more likely to modify this effect.