Why do people shrink?

Did you ever see the movie Honey, I shrunk the kids? It's about a wacky dad (who's also a scientist) who accidentally shrinks his kids with his homemade miniaturizing invention. Oops! ____1____.
For older people, shrinking isn't that dramatic or sudden at all. It takes place over years and may add up to only one inch or so off of their adult height (maybe a little more, maybe less), and this kind of shrinking can't be magically reversed, although there are things that can be done to stop it or slow it down. ___2___.
There are a few reasons. As people get older, they generally lose some muscle and fat from their bodies as part of the natural aging process. Gravity (the force that keeps your feet on the ground) take hold, and the bones in the spine, called vertebrae, may break down or degenerate, and start to collapse into one another. ___3___. But perhaps the most common reason why some older people shrink is because of osteoporosis.
Osteoporosis occurs when too much spongy bone tissue (which is found inside of most bones) is broken down and not enough new bone material is made. ___4___. Bones become smaller and weaker and can easily break if someone with osteoporosis is injured. Older people --especially women, who generally have smaller and lighter bones to begin with -- are more likely to develop osteoporosis. As years go by, a person with osteoporosis shrinks a little bit.
Did you know that every day you do a shrinking act? You aren't as tall at the end of the day as you are at the beginning. That's because as the day goes on, water in the disks of the spine gets compressed (squeezed) due to gravity, making you just a tiny bit shorter. Don't worry, though. ___5___.

A. They end up pressing closer together, which makes a person lose a little height and become shorter.
B. Once you get a good night's rest, your body recovers, and the next morning, you're standing tall again.
C. Over time, bone is said to be lost because it's not being replaced.
D. Luckily, there are things that people can do to prevent shrinking.
E. The kids spend the rest of the movie as tiny people who are barely visible while trying to get back to their normal size.
F. But why does shrinking happen at all?

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