Most people with sleep apnea are never diagnosed. However, brain scans have revealed that there may be a link between this condition and a form of dementia.
There are an estimated 22 million people in the United States living with sleep apnea according to the American Sleep Apnea Association (ASAA).
Sleep apnea is a condition that causes a person to stop breathing during the night and it can happen infrequently or often.
When a person experiences sleep apnea often, doctors refer to it as obstructive sleep apnea. And if left untreated, it can lead to a variety of cardiovascular health problems, including high blood pressure, stroke and even heart failure.
Researchers have also linked it to depression and type 2 diabetes.
"Recent research has linked sleep apnea to an increased risk of dementia," notes Dr. Diego Z. Carvalho, a neurology fellow at the Mayo Clinic in Rochester, MN.
He along with colleagues, has authored a study to investigate a potential relationship between sleep apnea and a specific Alzheimer's biomarker.
This biomarker is a protein called tau, which is abundant in the brains of people with Alzheimer's. It’s the Tau proteins that then form tangles that are identified through brain imaging studies,
"A person normally has fewer than five episodes of apnea per hour during sleep," states Dr. Carvalho.
The problem is that most people don’t even know they have it.
The ASAA report that approximately 80 percent of people with moderate-to-severe obstructive sleep apnea are never diagnosed.
In an effort to determine which of the participants experienced sleep apnea, researchers asked their bed partners to be on the lookout for episodes of stopped breathing during the night. In total 288 people 65 years of age and older took part in the study. None of the subjects had any signs of cognitive impairment.
In addition to asking each of the participants' bed partners, the researchers also used medical imaging studies to determine the presence of tau protein in their brains.
One area they looked at specifically is called the entorhinal cortex area. This area is known to develop tau tangles. And as part of the temporal lobe it plays a role in memory, navigation, and time perception.
Which came first?
Dr. Carvalho and colleagues found a link between sleep apnea and a higher presence of tau in the brain.
In total 43 people experienced apnea episodes as revealed by the overnight monitoring process. Those same people experienced a 4.5 percent higher incidence rate of tau proteins in the entorhinal cortex than those without sleep apnea.
This increase was identified after the team took into consideration other factors, such as age, sex, cardiovascular risk factors, and other sleep issues.
And while the medical community considers these results to be preliminary. the research team is set to present them at an upcoming American Academy of Neurology meeting in Philadelphia, PA.
Dr. Carvalho concludes that these results "raise the possibility that sleep apnea affects tau accumulation." However, he describes the findings as a chicken-and-egg scenario, adding: "It's also possible that higher levels of tau in other regions may predispose a person to sleep apnea."
An unclear link:
In prior studies, researchers have identified a link between dementia and sleep apnea. However, additional studies using larger sample sizes will need to be completed to truly determine the correlation.
The other factor with this study is that the methods used by the Mayo Clinic team didn’t actually determine whether the participants actually had sleep apnea, how severe it was, and whether they were already undergoing treatment.
Plus, if there is in fact a correlation between sleep apnea and dementia, researchers are still unclear as to why.
And while there have been a number of different theories presented no one know for sure.
One theory is that the brain consolidates memories during sleep, and interrupting this process might lead to memory issues.
The lack of oxygen reaching the brain during apnea episodes could also be a factor, especially if this puts stress on the brain.