Depression is an important, potentially modifiable dementia risk factor. However, it is not known whether effective treatment of depression through psychological therapies is associated with reduced dementia incidence. The aim of this study was to investigate associations between reduction in depressive symptoms following psychological therapy and the subsequent incidence of dementia.

National psychological therapy data were linked with hospital records of dementia diagnosis for 119808 people aged 65+. Participants received a course of psychological therapy treatment in Improving Access to Psychological Therapies (IAPT) services between 2012 and 2019. Cox proportional hazards models were run to test associations between improvement in depression following psychological therapy and incidence of dementia diagnosis up to eight years later.

Improvements in depression following treatment were associated with reduced rates of dementia diagnosis up to 8 years later (HR = 0.88, 95% CI 0.83–0.94), after adjustment for key covariates. Strongest effects were observed for vascular dementia (HR = 0.86, 95% CI 0.77–0.97) compared with Alzheimer's disease (HR = 0.91, 95% CI 0.83–1.00).

Reliable improvement in depression across psychological therapy was associated with reduced incidence of future dementia. Results are consistent with at least two possibilities. Firstly, psychological interventions to improve symptoms of depression may have the potential to contribute to dementia risk reduction efforts. Secondly, psychological therapies may be less effective in people with underlying dementia pathology or they may be more likely to drop out of therapy (reverse causality). Tackling the under-representation of older people in psychological therapies and optimizing therapy outcomes is an important goal for future research.

Affective symptoms are associated with cognition in mid-life and later life. However, the role of cardiometabolic risk in this association has not been previously examined.

To investigate how cardiometabolic risk contributes to associations between affective symptoms and mid-life cognition.

Data were used from the National Child Development Study (NCDS), a sample of people born in Britain during one week in 1958. Measures of immediate and delayed memory, verbal fluency and information processing speed and accuracy were available at age 50. Affective symptoms were assessed at ages 23, 33 and 42 years and a measure of accumulation was derived. A cardiometabolic risk score was calculated from nine cardiometabolic biomarkers at age 44. Path models were run to test these associations, adjusting for sex, education, socioeconomic position and affective symptoms at age 50.

After accounting for missing data using multiple imputation, path models indicated significant indirect associations between affective symptoms and mid-life immediate memory (β = −0.002, s.e. = 0.001, P = 0.009), delayed memory (β = −0.002, s.e. = 0.001, P = 0.02) and verbal fluency (β = −0.002, s.e. = 0.001, P = 0.045) through cardiometabolic risk.

These findings suggest that cardiometabolic risk may play an important role in the association between affective symptoms and cognitive function (memory and verbal fluency). Results contribute to understanding of biological mechanisms underlying associations between affective symptoms and cognitive ageing, which can have implications for early detection of, and intervention for, those at risk of poorer cognitive outcomes.