Mood index, sleep duration and risk of all-cause and cause-specific dementia: a prospective analysis of 429,761 UK Biobank participants

Aim Psychological factors such as mood and other mental health status may be associated with the development of dementia. However, a comprehensive mood index that reflects the overall mood status and dementia risk is lacking. While it is known that mood status and sleep influence each other, and both are associated with dementia, the synergistic effect of mood status and sleep on risk of dementia is unknown. Subject and Methods In this study, we examined the relationship between mood index, sleep duration and dementia in 429,761 participants from the UK Biobank. Each participant’s mood index (0 [worst] – 20 [best]) was determined on the basis of 20 mood behaviours. The mood index was divided into five groups. Three mood dimensions were also explored in relation to dementia. Sleep duration (h) was divided into four groups. Cox proportional hazard models were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs) for the association between mood, sleep duration and dementia (all-cause dementia, Alzheimer’s disease (AD) and vascular dementia (VD)). Results Compared to mood index 16–20, the HRs (95%CI) between mood index and all-cause dementia were 1.88 (1.62, 2.17), 1.47 (1.30, 1.67), 1.28 (1.14, 1.44) and 1.10 (0.97, 1.26). Similar findings were observed in the relationships between mood dimensions and the risk of dementia. In addition, compared to sleep duration (6–9 h), the HRs (95%CI) between other sleep durations and all-cause dementia were 1.39 (1.25, 1.54), 1.26 (1.15, 1.37) and 2.92 (2.30, 3.72). There was a synergistic effect between mood index and sleep duration on the risk of dementia. Conclusion Low mood index increased the risk of dementia. In addition, both long sleep duration (≥9 h) and short sleep duration (<6 h) increased the risk of dementia. There was a synergistic effect between mood index and sleep duration on the risk of dementia.