A new study, to be presented at the upcoming American Academy of Neurology's 71st Annual Meeting in Philadelphia, reveals a connection between sleep apnea and increased levels of a toxic brain protein commonly associated with Alzheimer's disease. These findings bolster the growing body of evidence linking sleep problems with the onset of neurodegenerative conditions.

It is becoming increasingly clear that sleep plays an incredibly important role in our overall cognitive health. Disrupted sleep has long been associated with dementia and Alzheimer's disease, however scientists have only recently started to unpack exactly how bad sleep is linked with cognitive decline.

This new study examined the link between increased levels of tau and episodes of stopped breathing during sleep. Tau is one of two proteins strongly implicated in the neurodegenerative effects associated with Alzheimer's disease.

The research looked at 288 subjects over the age of 65 with no diagnosed cognitive impairments. The subjects' partners were quizzed as to whether they have witnessed apnea episodes in their partners. All 288 subjects also underwent positron emission tomography (PET) to track tau levels in the brain, particularly in a temporal lobe area known to regulate memory. Those subjects who were reported to suffer from apneas displayed on average around 5 percent higher tau levels compared to those subjects with no observed apnea.

The research is not without limitations of course. For example, there is no evidence those subjects in the study with higher tau levels suffered from any relevant cognitive impairment. Also, alongside a small sample size, there is the big question of causation. Diego Carvalho, a researcher on the project, is frank about the study's inability to prove causation and says further work is certainly needed to understand how bi-directional this relationship is.

"Our research results raise the possibility that sleep apnea affects tau accumulation," says Carvalho. "But it's also possible that higher levels of tau in other regions may predispose a person to sleep apnea, so longer studies are now needed to solve this chicken and egg problem."

A study published last week demonstrating how deep slow wave sleep can potentially clear the brain of toxic proteins points to a compelling causal hypothesis, one that could explain how sleep apnea actively increases the accumulation of tau in the brain. Previous research has found that subjects suffering from sleep apnea may not effectively reach deep sleep stages due to the disruptions caused by phases of interrupted breathing. This chronic lack of deep sleep could, over many years, increase a person's risk for developing Alzheimer's due to the brain's inability to effectively wash out all the toxic proteins.

All these ideas are still resolutely hypothetical, as Alzheimer's research has recently hit a crisis point following years of failed human clinical trials. With scientists increasingly looking to novel research areas in the hopes of finding an effective way to prevent, or at least slow, the onset of age-related cognitive decline, it seems like sleep hygiene may play an important role in keeping our minds healthy in our senior years.

The new research will be presented in May at the American Academy of Neurology's 71st Annual Meeting in Philadelphia.