new research suggests. A U.K. Biobank study of more than 500,000 individuals also showed that excessive daytime sleepiness was associated with increased risk for Alzheimer’s disease.
“Addressing sleep problems in middle-age may play a role in improving brain health,” said lead author Lei Gao, MD, assistant professor of anesthesia at Harvard Medical School and associate scientist in the division of sleep and circadian disorders at Brigham and Women’s Hospital, both in Boston.
The findings were presented at the virtual annual meeting of the Alzheimer’s Association International Conference 2020.
Intricately linked
Sleep disturbances are common and on the rise around the world. In recent years, researchers have become increasingly aware of the intricate link between sleep health and brain health, Dr. Gao noted.
The current study included 502,538 individuals from the U.K. Biobank (mean age, 57 years) who were free from Alzheimer’s disease at baseline. They were followed for up to 12 years. The participants self-reported sleep traits, including hours of nighttime sleep, daytime sleepiness, sleep apnea diagnosis, snoring, and napping. Researchers determined Alzheimer’s disease diagnoses from hospital admissions and from death registries.
In addition to adjusting for age, sex, education, and ethnicity, the full model adjusted for socioeconomic status, body mass index, physical activity, smoking and alcohol use, cardiovascular diseases and risk factors, neurological diseases, respiratory diseases, depression/anxiety, and medication use. Over the course of a mean follow-up of 6.4 years, 932 participants developed Alzheimer’s disease.
Complex disorder
Compared with those who got an average of 6-9 hours of sleep per night, those getting more than 9 hours had a higher risk for Alzheimer’s disease (hazard ratio, 2.04; 95% confidence interval, 1.56-2.67; P < .001). Having sleep apnea also raised the risk significantly (HR, 2.05; 95% CI, 1.23-3.42; P = .006), as did daytime sleepiness (HR, 1.56; 95% CI, 1.18-2.03; P = .001).
Dr. Gao noted that daytime sleepiness and sleep apnea remained predictive after controlling for sleep duration. “In fact, all three sleep traits remained associated with Alzheimer’s disease within the same model, suggesting some degree of independence.”
Interestingly, snoring, which is a common symptom of sleep apnea, was not linked to Alzheimer’s disease risk. The “vast majority” of people who snore don’t meet criteria for a diagnosis of sleep apnea, which was particularly true for this large cohort of relatively healthy study participants, Dr. Gao noted.
“Sleep apnea is a complex, multisystemic sleep disorder associated with obesity, high blood pressure, and often other heart problems,” he said.
He added that, as an anesthesiologist, he is particularly wary if patients have this condition, “given their increased risk for airway difficulties, adverse cardiac events, postoperative respiratory complications, and confusion or delirium, which is also associated with higher risk for eventual Alzheimer’s disease and death.”
These multisystemic factors may be driving the link to Alzheimer’s disease. “We certainly need to address this better as the population ages and obesity rates rise,” Dr. Gao said.