Tangled Links Between Sleep, Dementia, and Obesity

Bound in SleepLet’s start at the end. Sleep is important. New publications remind us that inadequate sleep is a risk factor for both dementia and obesity. That risk mingles with other risks. Too little sleep brings problems with mood, physical function, and immunity. Those effects show up pretty quickly. But longer term effects are harder to pin down and that’s what this new research tries to address. Does too little sleep cause obesity and dementia? Or is it the other way around? For that matter, is obesity contributing to dementia?

While the links are unmistakable, we will likely debate causality for some time to come.

Sleep and Risk of Dementia

The study creating the biggest stir appeared in Nature Communications yesterday. Séverine Sabia and colleagues reported 7,959 subjects followed for 25 years from mid-life. They found a 30 percent increase in the risk of dementia from persistent short sleep duration at ages 50, 60, and 70. This risk was independent of social, demographic, behavioral, cardiac, metabolic, and mental health factors.

Neurology professor Kristine Yaffe was not involved with this study, but she told the New York Times:

“It would be really unlikely that almost three decades earlier, this sleep [pattern] was a symptom of dementia, so it’s a great study in providing strong evidence that sleep is really a risk factor.”

Erik Musiek, who runs the Center on Biological Rhythms and Sleep at Washington University in St. Louis, was a bit more cautious:

“I don’t know that this study necessarily seals the deal, but it gets closer because it has a lot of people who were relatively young. There’s a decent chance that they are capturing people in middle age before they have Alzheimer’s disease pathology or plaques and tangles in their brain.”

Obesity, Dementia, and Sleep

Among the variables for which Sabia et al accounted was BMI. This is important, because other studies are documenting a relationship between BMI at mid-life and the risk of dementia later in life. In the American Journal of Epidemiology, a new study by Jinlei Li et al finds that obesity for people in their forties had a strong association with dementia risk later in life. However, BMI was not so strongly associated at later ages and, in fact, became reversed after the age of 70.

In an invited commentary on this research, Willa Brenowitz explains that much work remains to understand this relationship. We need to understand when obesity can contribute to dementia and when dementia leads to weight loss. But she goes on to say the most helpful research would serve to isolate specific mechanisms and hypotheses regarding BMI, body composition, and dementia.

The final piece of this puzzle is the link between obesity and poor sleep. It is clear that obesity can interfere with restful sleep. But poor sleep can also contribute to weight gain. The relationship likely runs in both directions.

At the end of the day, we come back to where we started. Sleep is important.

Click here for new study of sleep and dementia and here for further reporting on it. For the study by Li et al on obesity and dementia, click here and then here for the Brenowitz commentary. Finally, for perspective on sleep and obesity, click here and here.

Bound in Sleep, painting by Arshile Gorky / WikiArt

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April 21, 2021