More than 18 million American adults have sleep apnea. The condition is more common in the elderly, especially those with Alzheimer’s disease.
Could sleep-disordered breathing, also known as sleep apnea, be one of the risk factors for Alzheimer’s disease? A recent study explored this association in elderly patients with normal cognitive function.
According to the study, the biochemical signs of Alzheimer’s disease might be detectable years before any symptoms are seen, and these early signs in the elderly may be associated with sleep apnea.
The study was conducted by Ricardo S. Osorio, MD, and colleagues from the Center for Brain Health at New York University to investigate the link between sleep apnea and Alzheimer's disease.
Sleep apnea is a condition in which breathing repeatedly stops and starts during sleep.
The objective of the study was to find out whether body chemicals associated with Alzheimer’s disease were found in normal functioning elderly people who had sleep-disordered breathing. Sleep apnea is one of the most common sleep-disordered breathing conditions.
The researchers recruited 68 elderly patients with normal mental function. The participants were monitored in their homes for two nights to diagnose possible sleep-disordered breathing by measuring breathing pattern abnormalities and the saturation levels of oxygen in the blood.
Then the researchers conducted several marker tests to predict the risk of Alzheimer’s disease. A marker is a chemical, usually in a body fluid, that can be measured to detect an existing or future disease condition.
Participants' cerebrospinal fluid was tested to confirm the presence of at least one of the three markers associated with Alzheimer’s, i.e., P-Tau, T-Tau and Aβ42.
The researchers also conducted FDG-PET (FDG-Positron Emission Tomography) scans of the brain to measure how glucose was metabolized. Basically, a radioactive chemical called FDG was injected into the bloodstream and its concentration in the brain was studied.
Brain PET scans with a chemical called Pittsburg compound were also conducted to measure amyloid, an abnormal collection of proteins that has been known to be associated with Alzheimer’s disease. Structural magnetic resonance imaging (MRI) scans were performed to measure the volume of the hippocampus, an area in the brain that plays a key role in memory.
An abnormal result in any of the above markers has been reported to be an early sign of Alzheimer’s disease onset.
Initial findings did not show any significant links between sleep apnea and early markers of Alzheimer’s disease.
“Our study did not determine the direction of the causality, and, in fact, didn’t uncover a significant association between the two, until we broke out the data on lean and obese patients,” said Dr. Osorio.
The researchers measured participants' body mass index (BMI), a measure of body shape based on weight and height. Participants who had BMI less than 25 kg/m2 were classified as lean.
The lean group of subjects had several specific and non-specific markers of Alzheimer’s risk. They had increased levels of P-Tau and T-Tau, shrinking of the hippocampus on MRI and lowered glucose metabolism.
Obese patients, who were defined as those with BMI higher than 25 kg/m2, did not exhibit similar significant signs.
Thus the results showed that in lean patients with normal mental functioning, there was an association between sleep-disordered breathing and chemicals that predict the risk of Alzheimer’s disease.
According to the authors, this association might help explain the high rates (30 to 80 percent) of sleep apnea in the elderly.
“We don’t know why it becomes so prevalent, but one factor may be that some of these patients are in the earliest preclinical stages of Alzheimer's disease,” said Dr. Osorio.
The authors conceded that an association does not necessarily mean that there is a direct causal relationship. They plan to conduct future studies to determine if sleep apnea is a direct cause of Alzheimer’s or vice versa.
“Our next study will involve treating our subjects and re-testing for these same Alzheimer’s markers to see whether treatment makes a difference. If it does, we hope the results would encourage more people to seek a diagnosis if they suspect sleep apnea,” one of the study researchers, Janna Mantua, research scientist at the New York University Sleep Disorders Center told DailyRx.
“If sleep-disordered breathing is indeed a risk factor for Alzheimer’s, this population of cognitively normal subjects is definitely of interest because we feel that we may be able to stabilize or even reverse cognitive decline if we catch it early enough,” said Mantua.
The study results were presented in May at the American Thoracic Society Conference in Philadelphia, Pennsylvania.
These findings are part of an abstract presented at a conference and should be considered preliminary until the entire study is published in a peer-reviewed journal.
No relevant financial relationships or conflicts of interest were disclosed.