Why do older people wake up so early?

There are many jokes about old people waking up before the sun, and even more jokes about the late sleeping habits of teenagers. It turns out there’s some truth: The time our bodies naturally fall asleep and wake up is not only part of our genetics, but also part of the natural aging process.

As we age, our bodies change both internally and externally, which is a major factor behind the sleep changes that occur later in life. “As with most things that change as we age, there’s not just one reason, and they’re all interconnected,” said Cindy Lustig, a psychology professor at the University of Michigan.

We asked Lustig and other experts to break down the main reasons why this happens and what you can do about it if you just want those few extra hours of Zzzs.

Like other aspects of our physical and mental health, the brain becomes less responsive as we age.

“The brain’s wiring is probably not sensing…and responding to input as well as it should, because it’s an aging brain,” said Dr. Sairam Parthasarathy, director of the Center for Sleep and Circadian Rhythm Sciences at University of Arizona Health Sciences. This information includes sunset, sunlight, meals, social cues, and physical activity that help us mark where we are in the day.

“These are all what we call time givers, or they give time to the brain,” he said. In other words, they help the brain determine where it is in the 24-hour circadian cycle.

So for a younger person, dinner time can help the brain understand that bedtime is in a few hours; for an older person, this connection may not occur.

The nerves that are supposed to give the brain temporal signals underwent the same amount of stress. degeneration than the brain, Parthasarathy said. TIts inability to perceive temporal cues partly explains why older people tend to tire before their children or grandchildren. And, as a result, wake up fully rested and earlier than the rest of the world.

“Interestingly, one reason appears to be that the vision changes that occur with age reduce the intensity of the degree of light stimulation our brains receive, which plays an important role in ‘tuning’ our circadian clock and keeping it on track,” Lustig said.

Parthasarathy explained that this is especially true for people with cataracts, a common eye disease that affects more than 50 percent of Americans aged 80 and older, according to the National Institutes of Health. Cataracts cause blurred vision, double vision, and general difficulty seeing.

“If there are cataracts, evening light does not penetrate the eyes as much, so according to the brain, sunset is earlier than when it actually sets,” Parthasarathy said.

Why is this important? As less light enters the eyes due to vision problems caused by cataracts, the body begins to release melatonin (the sleep hormone) earlier than it should. In younger people, melatonin “starts to increase after sunset,” says Parthasarathy, which is why we usually feel tired a few hours later. For people with cataracts whose brain thinks sunset was earlier, their perception of sunset is earlier, making them tired earlier in the evening. And going to bed earlier means waking up earlier.

“There is some evidence that cataract removal surgery can help improve sleep quality and duration by helping these light signals pass through,” Lustig said.

Parthasarathy says if you’re experiencing this problem, you should ignore the advice to put away screens and expose yourself to bright light in the late evening. This might mean taking a walk outside before sunset, reading a book on a glowing iPad, installing artificial lighting for your home, or watching TV on a glowing screen.

These bright lights will tell the brain that the sun hasn’t set yet, which will dampen melatonin production, he said. To help you stay up a little later (and therefore sleep a little later), Parthasarathy advises trying these things 30 to 60 minutes before sunset, which varies depending on the time of year and where in the United States you live.

Exactly how long you should expose yourself to bright light varies and may take some trial and error, but he said you should aim for around two hours of exposure — and you should definitely keep the lights on after sunset.

Lustig added that you should avoid alcohol before bed – “whileA night cap may make you sleepy, but it actually disrupts the quality of your sleep. Additionally, she said exercise can help you sleep better and morning sun can help your circadian clock track the sunrise and set signals.

Overall, changes in sleep habits are a part of life. Although some of these factors are beyond your control, you can also counteract them by adopting healthy habits to get optimal rest.

The original version of this story was published on HuffPost earlier.