, according to a new analysis of data from the Whitehall II cohort study.
Dr. Séverine Sabia
Previous work had identified links between short sleep duration and dementia risk, but few studies examined sleep habits long before onset of dementia. Those that did produced inconsistent results, according to Séverine Sabia, PhD, who is a research associate at Inserm (France) and the University College London.
“One potential reason for these inconstancies is the large range of ages of the study populations, and the small number of participants within each sleep duration group. The novelty of our study is to examine this association among almost 8,000 participants with a follow-up of 30 years, using repeated measures of sleep duration starting in midlife to consider sleep duration at specific ages,” Dr. Sabia said in an interview. She presented the research at the 2021 Alzheimer’s Association International Conference.
Those previous studies found a U-shaped association between sleep duration and dementia risk, with lowest risk associated with 7-8 hours of sleep, but greater risk for shorter and longer durations. However, because the studies had follow-up periods shorter than 10 years, they are at greater risk of reverse causation bias. Longer follow-up studies tended to have small sample sizes or to focus on older adults.
The longer follow-up in the current study makes for a more compelling case, said Claire Sexton, DPhil, director of Scientific Programs & Outreach for the Alzheimer’s Association. Observations of short or long sleep closer to the onset of symptoms could just be a warning sign of dementia. “But looking at age 50, age 60 ... if you’re seeing those relationships, then it’s less likely that it is just purely prodromal,” said Dr. Sexton. But it still doesn’t necessarily confirm causation. “It could also be a risk factor,” Dr. Sexton added.
Multifactorial risk
Dr. Sabia also noted that the magnitude of risk was similar to that seen with smoking or obesity, and many factors play a role in dementia risk. “Even if the risk of dementia was 30% higher in those with persistent short sleep duration, in absolute terms, the percentage of those with persistent short duration who developed dementia was 8%, and 6% in those with persistent sleep duration of 7 hours. Dementia is a multifactorial disease, which means that several factors are likely to influence its onset. Sleep duration is one of them, but if a person has poor sleep and does not manage to increase it, there are other important prevention measures. It is important to keep a healthy lifestyle and cardiometabolic measures in the normal range. All together it is likely to be beneficial for brain health in later life,” she said.
Dr. Sexton agreed. “With sleep we’re still trying to tease apart what aspect of sleep is important. Is it the sleep duration? Is it the quality of sleep? Is it certain sleep stages?” she said.
Regardless of sleep’s potential influence on dementia risk, both Dr. Sexton and Dr. Sabia noted the importance of sleep for general health. “These types of problems are very prevalent, so it’s good for people to be aware of them. And then if they notice any problems with their sleep, or any changes, to go and see their health care provider, and to be discussing them, and then to be investigating the cause, and to see whether changes in sleep hygiene and treatments for insomnia could address these sleep problems,” said Dr. Sexton.