The Framingham Heart Study is a large population study that has been following a group of people and their children since 1948, producing a wealth of information about heart disease and other conditions. In this new study, the researchers looked at the existing data to understand how sleep could be linked with dementia. They looked at the self-reported sleep duration of 2,457 people in the study, to see whether variation in how long people sleep for was associated with variation in the risk of developing dementia.
The researchers looked back at how many hours of sleep participants thought they had in a day and how this changed between two points, 13 years apart. Ten years after these sleep assessments, the researchers looked to see who had developed dementia. Over the 10 years of follow up, 234 people in the study developed dementia, of which 181 were diagnosed with Alzheimer’s disease.
The team found that sleeping over nine hours a day was associated with an increased risk of developing dementia compared to sleeping under nine hours. Going from sleeping under nine hours to sleeping over nine hours was associated with a greater risk of developing dementia, while there was no increased risk of dementia for those who already slept over nine hours a day.
The results of thinking tests and brain scans were available for 2,238 people in the study. The researchers found that short sleep duration (under six hours) and long sleep duration (over nine hours) were associated with poorer performance on thinking tests. However, only longer periods of sleep were associated with lower brain volume, which is used as an indicator of brain shrinkage.
Dr Rosa Sancho, Head of Research at Alzheimer’s Research UK, said:
“While unusual sleep patterns are common for people with dementia, this study adds to existing research suggesting that changes in sleep could be apparent long before symptoms like memory loss start to show. Other studies have indicated a link between changes in sleep quality and the onset of dementia, and while this wasn’t measured in this study, it could be an important factor affecting sleep duration. Understanding more about how sleep is affected by dementia could one day help doctors to identify those who are at risk of developing the condition. This study used self-reported sleep information, which is not always reliable, so larger studies looking at a number of sleep-related factors will be needed to better understand this link.”