This is the link between a bad night's sleep and Alzheimer's

Fragmented sleep, marked by repeated wake-ups during the night and a need to nap during the day, could be an early sign of Alzheimer's disease, according to new research.

A study recently published in the journal JAMA Neurology found that adults with healthy memories who had disrupted circadian rhythms — also known as sleep cycles — had protein buildups of a substance called amyloid plaque, which can serve as an early sign of Alzheimer's.

The damage that causes Alzheimer's-associated memory loss can begin 15 or 20 years before symptoms of the disease become evident. Other studies have shown that there's a connection between poor sleep and Alzheimer's or dementia as well. This new study provides more evidence of that link, and indicates that sleep disruption might be a very early warning sign of future neurodegenerative disease.

The findings also suggest that working to treat sleep issues early may help protect brain health down the road — though more research is needed to find out.

A growing body of evidence

For the new study, researchers tracked the sleep cycles of 189 cognitively healthy adults with an average age of 66. They also analyzed their brains to look for Alzheimer's-related proteins and plaques.

Most of the participants had relatively normal sleep cycles, and 139 had no signs of amyloid protein buildup. Some of those people had sleep problems, but they could mostly be explained by age, sleep apnea, or other causes.

But the 50 subjects in the study whose brains had Alzheimer's-related proteins all had disrupted body clocks.

"It wasn't that the people in the study were sleep-deprived," lead study author Dr. Erik Musiek said in a press release. "But their sleep tended to be fragmented. Sleeping for eight hours at night is very different from getting eight hours of sleep in one-hour increments during daytime naps."

The researchers also disrupted the sleep rhythms of mice in another study and found that doing so led to a buildup of amyloid plaque in their brains.

Other recent research has shown that people who report sleeping poorly show more signs of Alzheimer's. One recent study found that even disrupting someone's sleep for a night could lead to a spike in Alzheimer's-related proteins.

To be clear, that doesn't mean that one night of bad sleep leads to Alzheimer's. But it does make sleep trouble even more disturbing than the tired feeling that lingers after a restless night — which is good motivation to fix poor sleeping habits.

The issue of causation

The big question that remains is whether bad sleep causes the protein buildup that's linked to Alzheimer's, or whether people whose brains are already changing have more trouble sleeping.

It's quite possible that both are true.

Some research has indicated that any sleep disruption seems to lead to brain changes (in mice and people). We know that sleep has a cleansing function and that in deep sleep our brain washes away some proteins that regularly build up.

But we also know that once these buildups exist, people have a harder time getting that cleansing deep sleep. In other words, regular poor sleep could lead to a vicious cycle that makes it harder to get the rest the brain needs.

The upside of all this is that it could mean that intervening to fix sleep problems early could lead to improved brain health down the road. There are plenty of reasons to try to get a good night's sleep — this seems to be an especially good one.