To understand the effects of sleep on our quality of life in old age, we have to know a little bit about how sleep works, why we sleep, and how sleep changes over time.
Basic but important facts about sleep.
We don’t actually know how much sleep you need per night. Not everyone needs eight hours.

Part of a normal sleep cycle involves almost being awakened. Five times a night is typical.
Sleep is not all about restoring your energy—maybe not even mostly.
Eighty-five year old person spends 250,000 hours in sleep about twenty-nine years of his or her life.

Newborns sleep a leisurely sixteen hours a day. Older adults usually get less than six.
The sleep cycle is born of conflict, like two teams competing in the ultimate soccer match: they play each other twenty-four hours a day and don’t stop until you’re dead.
Bioenergetic analysis shows the energy savings during sleep is only about 120 calories, the same as a bowl of soup. And your brain is mostly to blame for this. It’s the power hog of the body, taking 20 percent of the energy you consume and required to remain active 24/7 to keep you alive.
We sleep to learn.

Daylight brain is busy recording your various daily activities. Some are forgettable, some are important, and some need time for future processing. Your memory systems are constantly engaged. Memory is processed later that night, during slow-wave sleep.Throughout the deepest slumber, your brain reactivates the memories laid down during the day, the ones marked for later processing. People need to sleep not to rest but to learn.
The amount of that memory-inducing, garbage-collecting, completely useful slow-wave sleep (SWS) decreases as you get older. In your twenties, you spend about 20 percent of your nighttime bathing in its healing breakers. By the time you reach seventy, you spend about 9 percent.
Buried deep inside your brain is a little patch of neurons—only about twenty thousand cells strong—known as the suprachiasmatic nucleus. It contains the master pacemaker of the body, the cesium clock of human experience.

The SCN receives information about the time of day directly from the eyes, along neural trunks called retinal projections. The stress hormone cortisol is under tight circadian control. So is digestion.
The SCN exerts its rhythmic will via hormones, including its franchise player, melatonin. The hormone is made in a pea-size organ called the pineal gland. During the night, the SCN turns the pineal spigot to “on” and melatonin floods the blood. It’ll circulate all night long, not seriously reducing its levels until about 9:00 a.m.
As people age rhythm-inducing genes in the SCN declines. All of these have measurable effects on sleep and arousal, specifically targeting levels of melatonin and cortisol. Researchers believe these changes reverberate throughout the body—primarily, of course, in the ability to get a good night’s rest.
Like a song you just can’t keep out of your head, the brain replays over and over again at night what occurred in the daytime. And this function is also greatly diminished over the age of 60.
Sleep loss is associated with the loss of a number of socially lubricating behaviors, including executive function in younger people.
If you want to diminish cognitive decline in old age, you must start accruing good sleep habits in middle age.
Brain has many drainage systems. Acting like their urban counterparts, many become active at night. One of them is called the glymphatic system. The toxic waste is removed from the brain, and you pee it out in the morning. This convective system operates during slow-wave sleep, the same stage in which learning occurs.
For years it was thought that a chronic lack of sleep is a risk factor for many neurodegenerative diseases—including Parkinson’s, Huntington’s, and Alzheimer’s. Jet-lagged flight attendants (especially those logging long-haul international flights) have an unusual amount of hippocampal atrophy, a telltale sign of Alzheimer’s.
Everybody needs six and eight hours of sleep every night, no more and no less. If you get less than six hours, mortality risk rises 21 percent in women, 26 percent in men. If you get more than eight hours, mortality risk rises 17 percent in women, 24 percent for men.
Young men, for example, see a 129 percent greater mortality risk with sleep loss.
Seniors taking more than thirty minutes to fall asleep have an increased risk for anxiety disorders, and for a reason probably familiar to you.

Getting a good night’s sleep starts with paying attention to what you’re doing four to six hours before you go to bed. No caffeine six hours prior. No nicotine. No alcohol, either. Alcohol, legendary for inducing drowsiness, is actually a biphasic molecule possessing both sedating and stimulating properties. Drowsiness occurs initially; the stimulating effect much later.
Designate a place in your house where the only activity is sleep. That’s going to be the bedroom for most people. Don’t eat there, don’t work there, don’t have a TV there. Just sleep. (You might do one or two other activities there, but see the above admonition concerning exercise.)
People fall asleep ideally around 65 degrees. Make sure the room you just designated as Sleep Central is cool.
Go to sleep at the same time every night. Wake up at the same time every day. No exceptions.
If you can’t fall asleep after thirty minutes, don’t stay in bed. Get up and read a dead-tree (non-electronic) book. Especially one that’s boring.
Expose yourself to bright light during the day, dim light during the evening. This mimics what our brains were used to experiencing during our sojourn under the vast African skies.
Stay away from blue light.

That means laptops, TVs, mobile devices, or anything that radiates at 470 nanometers (the frequency of blue light). That wavelength has been shown to trick the brain into thinking it’s daylight. Arousal follows, and for a logical evolutionary reason. Blue is the color of sky, which the brain historically encountered only in the daytime. Fflux is a good app to install in your laptop to block the blue light.
Depression is associated with sleep fragmentation, and social interactions are powerful antidepressants. Social interactions also exert a surprisingly powerful cognitive load, giving the brain a real workout, preparing it for surfing the slow waves later that night.