The Simple Reason Why You Wake Up Earlier As You Age

Earlier wake times are part of the natural aging process.

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

“The wiring of the brain is likely not sensing…and responding to the inputs as well as it should because it’s an aging brain,” said Dr. Sairam Parthasarathy, the director of the Center for Sleep and Circadian Sciences at the University of Arizona Health Sciences. These inputs include sunset, sunlight, meals, social cues, and physical activity that help mark where we are in a 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 sense where it is in the 24-hour circadian cycle. 

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

The nerves that are supposed to give the brain time cues have undergone the same amount of degeneration as the brain, Parthasarathy said. This inability to sense time cues is part of the reason why older people tend to get tired before their children or grandchildren. And, as a result, wake up fully rested and earlier than the rest of the world.

The light our eyes take in is part of it, too.

“Interestingly, one of [the reasons] seems to be that the vision changes that come with age reduce the intensity of the degree of light stimulation that our brain receives, which plays an important role in ‘setting’ our circadian clock and keeping it on track,” Lustig said.

Parthasarathy explained that this is especially true for people with cataracts, a common eye condition that impacts more than 50% of Americans ages 80 and up, according to the National Institutes of Health. Cataracts cause blurred vision, double vision, and general trouble seeing.

“If there’s cataracts, the evening light doesn’t go into the eyes as much, so, according to the brain, sunset is earlier than when it actually set,” Parthasarathy said. 

Why does this matter? Since there is less light getting into the eyes because of the vision issues cataracts cause, the body starts to release melatonin (the sleep hormone) earlier than it should. For younger people, melatonin “starts rising after sunset,” Parthasarathy said, which is why you generally feel tired a few hours after. For people with cataracts whose brain thinks sunset was earlier, their perceived sunset is earlier, which makes them tired sooner in the evening. And going to bed sooner means waking up earlier.

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