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It is a well-known stereotype that older people sleep less than younger folks, often rising at like, 4AM. But even though it's a stereotype, there does seem to be some truth to this.

Like, surveys have found that many seniors wake multiple times in the wee hours before finally rising at the crack of dawn. This doesn't happen because their bodies need less shut-eye, though; older adults need just as much sleep as younger ones. And although sleep can be disrupted by many things associated with aging, like pain or medication, that's not the full story, either.

Instead, studies suggest there are some fascinating and sometimes bizarre reasons older adults may wake up with the chickens. Including this stuff called brain sand. Which is even weirder than brain sand sounds.

The general explanation here is that something changes with your circadian rhythm as you get older. That's the roughly 24-hour cycle your body is on, which affects everything from when you get tired to when you poop. But regarding what changes, the explanations vary.

A lot. Some of these ideas are pretty straightforward. For example, there's evidence that dying brain cells may play a role.

Hormone changes are also on the table. See, over the course of a day, your brain triggers the release of hormones into your blood that regulate your body's internal clocks. These hormones result in certain proteins being produced and broken down on a 24-hour cycle, and that influences things like when you naturally wake up in the morning.

So if something changed with those hormones, it makes sense that your sleep schedule would, too. And according to some evidence, that's what happens in older adults. Studies have found that as people age, more of these proteins are produced earlier in the day, which could trigger seniors to rise and shine in the wee hours.

Some scientists hypothesize that a hormone or some other molecule in the blood is responsible for this. And although it sounds reasonable to begin with, there's also a really weird study backing this up. In an experiment published in 2011, researchers took skin cells from eighteen people in their 20s and grew them in blood serum from eighteen people between 56 and 83 years old.

Serum that, presumably, had this age-dependent hormone or molecule in it. And suddenly, the younger cells started producing proteins earlier in the day, behaving like they were forty years older! Which is quite the result.

Now, more specifically than just “hormones,” it's also possible that melatonin could be involved here. That's one of the hormones that regulates sleep. Several studies have found that melatonin levels decline with age, and the reasons why vary from reasonable to almost ridiculous.

Like, it seems to happen partly because certain brain receptors and enzymes associated with melatonin dwindle, and possibly because the brain uses more melatonin over the years. But this might also be caused by something in the pineal gland called “brain sand.” Buckle up, because this stuff is about to get fascinating. The pineal gland is a soybean-sized organ in the center of your brain, and it releases melatonin and plays a big role in your circadian rhythm.

So, it's pretty important. But something weird happens to it as people age: In this gland, calcium deposits can form. Now, calcification occurs in other organs, too.

But the pineal gland has the highest rate of calcification of any organ in the body. One study found that in people aged forty to seventy, up to twenty-eight percent of the pineal gland could be studded with these chunks of calcium, also known as brain sand. It's little rocks… in your brain!

Scientists don't really know why these deposits happen, either. Some hypothesize it might be caused by vascular inflammation or reduced oxygen in the brain, both of which can occur more as people age. These scientists think either of these things might be causing stem cells in the pineal gland — that is, cells that can turn into other types — to transform into cells that produce bone.

That's right. Pineal calcification might be similar to the production of bone in the brain. Which should not be a thing!

For now, at least, that's just speculation. Still, researchers do know that brain sand reduces the amount of melatonin in the fluid around the brain and spinal cord. And that can lead to insomnia and other sleep disturbances, including waking up super early.

So, from dying cells to hormones to brain sand, there are tons of ideas about why older adults tend to rise so early. And it's possible that multiple factors might be at play here. In any case, there are so many ideas that some scientists speculate there might be an evolutionary reason behind all this.

It's called the “poorly sleeping grandparent hypothesis.” It's the idea that, back when most humans slept outside or in relatively open environments, it was beneficial for some people to stay up and remain vigilant for lions and other predators. And as a result, we evolved circadian rhythms that changed with age and ensured someone was always awake to act as a sentinel. This idea is cool, but it is just a hypothesis.

It's completely possible that our sleep schedules evolved for a different reason, or as a matter of chance. But it does kind of make you think: If older people have internal alarm clocks to save their families from man-eating lions, that's a pretty heroic reason to get up early in the morning and go to Denny's. Thanks for watching this episode of SciShow!

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