New research shows that obstructive sleep apnea (OSA) may put elderly people at greater risk of developing Alzheimer’s disease.
In the study, published in the American Thoracic Society’s American Journal of Respiratory and Critical Care Medicine, researchers report that biomarkers for amyloid beta, the plaque-building peptides associated with Alzheimer’s disease, increase over time in elderly adults with OSA in proportion to OSA severity.
That means individuals with more apneas per hour had greater accumulation of brain amyloid over time, the researchers explain.
Alzheimer’s afflicts about five million older Americans. OSA is more common, afflicting between 30 to 80 percent of the elderly, depending on how OSA is defined, according to the researchers.
“Several studies have suggested that sleep disturbances might contribute to amyloid deposits and accelerate cognitive decline in those at risk for AD,” said Ricardo S. Osorio, M.D., senior study author and assistant professor of psychiatry at New York University School of Medicine. “However, so far it has been challenging to verify causality for these associations because OSA and AD share risk factors and commonly coexist.”
The study included 208 participants, between the ages of 55 and 90, with normal cognition as measured by standardized tests and clinical evaluations. None of the participants was referred by a sleep center, used continuous positive airway pressure (CPAP) to treat sleep apnea, was depressed, or had a medical condition that might affect their brain function
The researchers performed lumbar punctures to obtain participants’ cerebrospinal fluid to measure soluble amyloid beta levels, then used positron emission tomography, or PET, to measure amyloid beta deposits directly in the brain in a subset of participants.
The study found that more than half the participants had OSA, including 36.5 percent with mild OSA and 16.8 percent with moderate to severe OSA.
From the total study sample, 104 participated in a two-year longitudinal study that found a correlation between the severity of OSA and an increase in amyloid deposits in the brain. That finding was confirmed in the subset of participants who underwent amyloid PET, which showed an increase in amyloid burden in those with OSA, according to the researchers.
Surprisingly, the study did not find that OSA severity predicted cognitive deterioration in these healthy elderly adults, the researchers noted.
According to Andrew Varga, M.D., Ph.D., study coauthor and a physician specializing in sleep medicine and neurology at the Icahn School of Medicine at Mount Sinai in New York, this suggests that these changes were occurring in the preclinical stages of Alzheimer’s.
“The relationship between amyloid burden and cognition is probably nonlinear and dependent on additional factors,” he said.
This finding may also be attributable to the study’s relatively short duration, highly educated participants, and the use of tests that fail to discern changes in cognitive abilities that are subtle or sleep-dependent, the researchers said.
The high prevalence of OSA the study found in these cognitively normal elderly participants and the link between OSA and amyloid burden in these very early stages of Alzheimer’s suggest the CPAP, dental appliances, positional therapy and other treatments for sleep apnea could delay cognitive impairment and dementia in many older adults, the researchers said.
“Results from this study, and the growing literature suggesting that OSA, cognitive decline, and AD are related, may mean that age tips the known consequences of OSA from sleepiness, cardiovascular and metabolic dysfunction to brain impairment,” Osorio said.
“If this is the case, then the potential benefit of developing better screening tools to diagnose OSA in the elderly who are often asymptomatic is enormous.”
Source: American Thoracic Society