One of the reasons we sleep, it now seems, might be to keep a range of illnesses–including cognitive diseases like Alzheimer’s and other dementias–at bay.

That they seem to be essential for lowering the risk of brain disorders, from the forgetfulness of senior moments to the more serious memory loss and cognitive decline of dementia and Alzheimer’s disease, may convince the Franklins of the world that sleep is not for the lazy.

Even older people without Alzheimer’s can experience changes in their sleep patterns, sleeping less and more lightly as they age.

But in the 1980s and 1990s, scientists began studying whether there was any causal relationship between sleep patterns and cognitive-test performance among older people without Alzheimer’s by studying them over longer periods of time.

Those studies suggested that people with poor sleep habits tended to perform worse on cognitive tests over time.

A year later, a biological explanation for why poor sleep might be linked to Alzheimer’s emerged.

Taken together with Spira’s discovery that levels of amyloid spiked during the day and dropped during sleep, Nedergaard’s findings gave further credence to the theory that sleep might perform a housekeeping function critical for warding off diseases like Alzheimer’s.

For that, researchers need two additional pieces of evidence: first, a clear correlation between disrupted sleep patterns and a higher risk for Alzheimer’s; and second, evidence that if these high-risk people improve their sleep, that risk falls.

For example, Volkow measured baseline amyloid levels in the brains of 20 healthy people ages 22 to 72 years, then scanned their brains again after each had a good night’s sleep and yet again after each was kept awake for about 31 hours straight.

After a loss of sleep, levels of amyloid were 5% more than after adequate sleep; the spikes were concentrated in parts of the brain involved in memory and higher thinking, which are typically affected in Alzheimer’s.

But seeing levels of amyloid change with more or less sleep doesn’t necessarily mean sleep habits are contributing to Alzheimer’s.

To make that case, researchers are studying people with disorders like sleep apnea, or those who work night shifts or keep irregular working hours, such as first responders, pilots and flight attendants.

For people with sleep apnea, for example, doctors can prescribe devices to wear during sleep to keep oxygen flowing more consistently to the brain so they don’t wake up.

If these efforts lower their likelihood of developing Alzheimer’s, that would make a strong case for a connection between lifelong sleep patterns and risk of dementia.

Even while these studies are being done, many experts believe the data are already strong enough to start educating at least older people, especially those at higher risk of developing Alzheimer’s, about improving their sleep habits.

“Even practical sleep-hygiene tips, where we teach people best practices like avoiding caffeine in the evening and darkening their room and staying off their phones, could help them sleep better,” she says.