Why do we sleep? Understanding the connection between sleep and Alzheimer’s Disease

Imagine waking up in the morning after a good night’s sleep. Your thinking is sharper, your memories are clearer, and you may even feel a lot happier about the day. Every organism studied by scientists has a period of sleep, although requirements for duration and physiological patterns may differ between species. Sleep is critical for memory, thinking, and physical health. Diseases or disorders that cause loss of sleep or changes in sleep patterns often lead to health problems. Our bodies let us know when we aren’t getting enough sleep and we all intuitively understand that sleep is important, but have you ever wondered exactly why humans need to sleep?

Scientists have researched this question for centuries and proposed several theories that could explain the puzzling need for sleep. One potential reason is energy conservation; by sleeping, we can save our energy for the times of day where we need it the most, such as when running from predators or searching for food. Humans are diurnal, so our period of intense activity takes place during daytime hours, making nighttime activity a bit of a waste.

Other scientists argue that sleep helps form new connections between neurons in the brain, especially after learning something new during the day. Sleep helps consolidate our memories, moving them from short-term to long-term storage, which is why getting a full night of sleep before a test is a much better idea than staying up all night studying for it.

Recent research, however, has led scientists to propose another function for sleep. According to this new theory, sleep helps remove toxic proteins from the brain, cleaning out the fluid between neurons and preventing accumulation of unwanted compounds. If true, this theory may implicate sleep in a broad class of neurodegenerative disorders caused by toxic protein buildup. One classic example of such disorders is Alzheimer’s, a disease characterized by progressive loss of memory and daily function.

Patients with Alzheimer’s often have aggregates of proteins in the brain, such as beta amyloid and tau. Though the explicit contribution of these proteins is not clear, both are closely associated with disease progression.

Interestingly, beta amyloid is also one of the key proteins that is removed during sleep, which has led scientists to posit that there may be a significant relationship between Alzheimer’s and sleep, a link that also seems to extend to neurophysiology.

Both sleep disorders and Alzheimer’s affect a region of the brain called the SCN. Often dubbed the central clock, the SCN controls circadian rhythms, synchronizing our body processes to a 24 hour daily cycle. Circadian rhythms are malleable, and can change with age; however changes in circadian rhythm – and the SCN – are particularly pronounced in Alzheimer’s patients.

Though preliminary, these findings provide novel avenues for treatment for patients with Alzheimer’s. Treatments that include bright light therapy or enforce regular sleep/wake times could be especially beneficial for those staying in assisted living facilities. 

Furthermore, this research underlines the importance of treating sleep disorders early in life to prevent Alzheimer’s later down the road. It’s estimated that 15% of Alzheimer’s cases arise from sleep disorders, so diagnosing and treating sleep problems is important in the fight to prevent Alzheimer’s. And even for those of us without sleep disorders, it’s important to maintain good sleep hygiene tips, like getting enough sleep every night and going to bed and waking up at consistent times. Not only will you feel better after a restful night of sleep, but you’ll be protecting your brain at the same time. 

Image by Michael Morgenstern