People whose reported sleep remained at six hours or less between ages 50 and 70 were more likely to develop dementia than those who consistently reported seven hours, a long-term study of British adults found.
The study, led by Dr. Séverine Sabia of Inserm and UCL, was published in Nature Communications in April 2021. Its broader analysis used data from 7,959 participants in Britain’s Whitehall II study. The 30% finding came from a separate analysis of 6,875 participants who were free of dementia at age 70 and had reported their sleep at least twice across the three age points.
Researchers asked participants how many hours they slept on an average weeknight and compared those reporting six hours or less with those reporting seven hours. After accounting for health and lifestyle factors, short sleep reported at age 50 was associated with a 22% higher dementia risk. At age 60, the estimate was 37% higher. The result at age 70 was less certain.
In the sleep-pattern analysis, participants whose sleep remained short had a 30% higher risk than those whose sleep remained at seven hours. A smaller analysis using wrist-worn devices also linked shorter measured sleep with higher dementia risk.
The 30% figure describes a relative difference between the groups, rather than a person’s chance of developing dementia. The study cannot establish whether short sleep caused the disease. It also did not test whether moving bedtime earlier would reduce the risk.
