Prolonged sleep disruption and deprivation might increase risk of Alzheimer's disease

/www.eurekalert.org

Public release date: 26-Sep-2011
Contact: Michael C. Purdy
Washington University School of Medicine
Marker for Alzheimer's disease rises during day and falls with sleep
Up-and-down cycle flattens as age disrupts pattern

A marker for Alzheimer's disease rises and falls in the spinal fluid in a daily pattern that echoes the sleep cycle, researchers at Washington University School of Medicine in St. Louis have found.

The pattern is strongest in healthy young people and reinforces a link between increased Alzheimer's risk and inadequate sleep that had been discovered in animal models. The brain's relative inactivity during sleep may provide an opportunity to finish clearing away the Alzheimer's marker, a byproduct of brain activity called amyloid beta. The body clears amyloid beta from the brain through the spinal fluid and other mechanisms.

In the new study, scientists report that the normal highs and lows of amyloid beta levels in the fluid that surrounds the brain and spinal cord begin to flatten in older adults, whose sleep periods are often shorter and more prone to disruption. In older adults with brain plaques linked to Alzheimer's disease, the ebb and flow is eradicated, and amyloid beta levels are close to constant.

The study is now online in Archives of Neurology.

"In healthy people, levels of amyloid beta drop to their lowest point about six hours after sleep, and return to their highest point six hours after maximum wakefulness," says Randall Bateman, MD, associate professor of neurology. "We looked at many different behaviors, and the transitions between sleep and wakefulness were the only phenomena that strongly correlated with the rise and fall of amyloid beta in the spinal fluid."

Bateman's laboratory conducted the study in partnership with Washington University's Sleep Medicine Center.

"We've known for some time that significant sleep deprivation has negative effects on cognitive function comparable to that of alcohol intoxication," says Stephen Duntley, MD, professor of neurology and director of the center. "But it's recently become apparent that prolonged sleep disruption and deprivation can actually play an important role in pathological processes that underlie diseases. This connection to Alzheimer's disease isn't confirmed yet in humans, but it could be very important."

Duntley notes that older adults often sleep less and have fewer periods of deep slumber. A number of factors linked to aging, such as reduced exercise levels, can disrupt the normal daily patterns of sleep and waking. These disruptions often become more pronounced as individuals age. The risk of Alzheimer's disease also increases with age.

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