Researchers at Oxford Population Health have found that there is little evidence to suggest that there is an association between sleep duration and risk of developing dementia, based on data collected by the UK Million Women Study. The results are published today in Alzheimer's & Dementia: The Journal of the Alzheimer's Association.
Disturbed sleep is common in people with dementia, which may be as a result of changes in the brain that affect our natural sleep cycles. Previous studies have suggested that disturbed sleep, including both long and short sleep duration, may also be a risk factor for dementia but findings have been inconsistent. Dementia is known to develop over a very long period of time and can start to cause changes in an affected person’s brain many years prior to diagnosis. As a result, dementia may lead to changes in sleeping patterns many years before diagnosis which could give rise to misleading associations between sleep duration and the short-term risk of dementia.
To assess whether or not sleep duration is associated with dementia risk, the researchers analysed data on usual sleep duration reported by 830,716 women, who were aged 60 on average and did not have any mention of dementia in their health records. The researchers then followed the women through their medical records to identify which women later developed dementia. The results of the study focus on associations with risk in the period 15 or more years after the initial data collection to reduce the likelihood that reported sleep duration could have been impacted by as yet undiagnosed dementia.
The participants most commonly reported a normal sleep duration of seven to eight hours (67%), with 23% reporting short sleep duration of six hours or less and 10% reporting long sleep duration of nine hours or more. Key findings:
- 15,146 women had dementia recorded in their health records 15 or more years after the initial reporting on sleep duration;
- Short sleep duration (six hours or less) was associated with a slightly higher dementia risk (1.08 [1.04 – 1.12]) when compared with a normal sleep duration (seven-eight hours);
- Women who reported long sleep duration (nine hours or more) were not at increased risk of dementia (1.04 [0.99 – 1.09]);
- The associations did not appear to differ across dementia types (Alzheimer’s disease, vascular dementia, unspecified dementia) for either short or long sleep duration when compared to normal sleep duration.
Dr Angel Wong, Early Career Fellow at Oxford Population Health and lead author of the study, said ‘The results of this study indicate that, compared with normal sleep duration, longer sleep duration is not a risk factor for dementia. There was some evidence that shorter sleep duration may be associated with some increase in dementia risk but any such increase is likely to be very small.’