Poor Sleep Tied to Increase in Alzheimer's-linked Protein Tau

Scientists have linked lower quality sleep to higher levels of a sticky plaque in the brain that researchers believe could cause Alzheimer's disease.

Researchers behind the study published in the journal Science Translational Medicine investigated whether the amount of deep sleep a person enjoys each night correlates with the levels of tau protein in their brain. Although the cause of Alzheimer's disease is unknown, researchers believe the build-up of amyloid beta proteins, followed by tau protein, in the brain could cause the erosion of cognitive abilities.

Read more: Common herpes virus could cause 50 percent of Alzheimer's disease cases, expert says

Deep or slow wave sleep, which enables the brain to store and process new information, was the focus of the research. To study the potential link between tau build-up and sleep levels, the team recruited 119 people who were aged 60-years-old or over. Of the total, 80 percent of the participants were healthy while the remainder showed mild signs of cognitive decline.

The volunteers each kept a diary of their sleeping patterns for between two to six days, including if they napped in the day. They were also given EEG monitors and sensors, which they wore as they slept to collect data on their brain waves.

Of the total participants, 104 donated cerebrospinal fluid so the researchers could assess the liquid for evidence of amyloid beta and tau; 38 had brain scans to detect the proteins; and 27 underwent both procedures.

The data revealed those who enjoyed fewer hours of slow wave sleep were more likely to have higher levels of tau in their brains.

Dr. Brendan Lucey, first author of the study and assistant professor of neurology at the Washington University Sleep Medicine Center, commented in a statement: "The key is that it wasn't the total amount of sleep that was linked to tau, it was the slow-wave sleep, which reflects quality of sleep.

"The people with increased tau pathology were actually sleeping more at night and napping more in the day, but they weren't getting as good quality sleep."

He continued: "What's interesting is that we saw this inverse relationship between decreased slow-wave sleep and more tau protein in people who were either cognitively normal or very mildly impaired, meaning that reduced slow-wave activity may be a marker for the transition between normal and impaired."

The researchers hope their findings could help to create screening programs for Alzheimer's disease, which affects some 5.7 million adults in the U.S..

"A major implication of our study is that measuring non-rapid eye movement slow wave activity or other changes in sleep-wake activity (along with other factors) may be a way to non-invasively and inexpensively screen for risk for cognitive decline due to Alzheimer's disease," Lucey told Newsweek. "This would be very helpful in future clinical trials and possibly screening in the clinic."

Lucey also acknowledged the study was limited because it was cross-sectional, meaning the researchers were unable to pinpoint whether slow wave activity decrease first and then tau accumulates, or vice versa.

"Future longitudinal studies where participants are followed over time will be needed to answer these questions," he told Newsweek.

Addressing sleep disorders and health more broadly, he continued: "Sleep disorders have been associated with multiple medical problems including heart disease, diabetes, as well as Alzheimer's disease. I recommend that patients with a sleep concern or evidence of a sleep disorder should be referred to a sleep specialists for evaluation and treatment if needed."

However, Dr. James Pickett, head of research at the charity Alzheimer's Society, who was not involved in the study, was only cautiously optimistic about the findings.

He told Newsweek: "Although this small study implies that older people who have fewer hours of deep sleep are more likely to have changes in their brain—it doesn't tell us if poor sleep is the cause of these changes. Or if it could in fact be an early symptom of Alzheimer's.

"We know there's a link between sleep and dementia, but there's still a lot to learn about this relationship."

"It's too soon to say if trying to change our sleep habits might affect our chances of developing dementia, but there's good evidence that being physically active and eating healthily can reduce the risk," said Pickett. He advised members of the public to choose an apple of a packet of chips, "and get out as much as possible."

The tau protein isn't the only potential cause of Alzheimer's disease, experts believe. Last year a paper published in the journal Frontiers in Aging Neuroscience indicated a strain of the herpes virus could trigger the neurodegenerative disease.

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Researchers believe the quality of sleep a person is linked to their risk of developing dementia. Getty Images

This article has been updated with comment by Dr. Brendan Lucey.