A study has found that a lack of sleep over a prolonged period of time can increase the risk of Alzheimer’s disease.

Led by the Washington University School of Medicine and published in the journal Brain, it found that just one night of disrupted sleep increased amyloid beta in the brain. This is a protein that has been associated with Alzheimer’s disease.

Another week of poor sleep can then subsequently increase a protein called tau, which has been linked to brain damage in Alzheimer’s and other neurological diseases. However, for most, levels of both returned to normal relatively quickly. It’s only people with longer sleep problems that may be at risk.

"We showed that poor sleep is associated with higher levels of two Alzheimer's-associated proteins," senior author David Holtzman said in a statement. "We think that perhaps chronic poor sleep during middle age may increase the risk of Alzheimer's later in life."

The study was based on an admittedly small group of people, just 17 healthy adults aged between 35 and 65. They had no prior sleep problems and were given an activity monitor for their wrists to wear for two weeks to measure their sleep.

After five or more nights with the monitor at home, the participants then went to a specially designed sleep room at the School of Medicine. This was dark, soundproof, and climate-controlled, ensuring a sound night’s sleep, with electrodes monitoring their brain waves.

However, only half of them were given a sound night’s sleep. Half slept with headphones on, while the other half of the group were sent a series of beeps that gradually got louder and forced the participants from a deep sleep into a shallower sleep. Those who this occurred to reported feeling tired and unrefreshed in the morning.

Using a spinal tap, the researchers then measured amyloid beta and tau levels in the brain. They found a 10 percent increase in the former after the single night of disrupted sleep, and an increase in the latter for those who had slept poorly for more days at home. This is thought to be because amyloid levels change more quickly than tau levels.

The researchers noted that both amyloid beta and tau levels would return to normal after a person had a good night’s sleep. But for people with chronic sleep problems, it could lead to “chronically elevated amyloid levels” said co-first author Yo-El Ju.

They pointed out that more sleep wouldn’t necessarily decrease the risk of developing Alzheimer’s, but it did seem that bad sleep could temporarily increase protein levels associated with the disease.