A York University review examined sleep duration, sedentary time and physical activity, while the reported associations do not establish cause and effect.
Researchers at York University in Canada analyzed data from 69 earlier studies to examine dementia in relation to three daily factors: sleep duration, time spent sitting and physical activity. The findings were published in PLOS One.
The analysis associated sleeping fewer than seven hours a night with an 18% higher dementia risk, and sleeping more than eight hours with a 28% higher risk. The researchers also found associations with sitting for more than eight hours a day and getting less than 150 minutes of physical activity a week.
These are statistical associations and do not by themselves show that too little or too much sleep, or sedentary behavior, causes dementia. The researchers analyzed existing studies rather than testing a specific sleep routine in an experiment.