The next time someone asks you how tall you are, keep in mind that your answer might depend on the time of day. In the morning, when you wake up, you're taller than at night, when you go to bed.
The spine is made of twenty-nine vertebrae and the tailbone. Sandwiched between these hard vertebrae are what are known as intervertebral disks, which act as shock absorbers and protect our spinal cord. These disks can compress or expand, and this mechanism is what enables us to move our spine.
Intervertebral disks are made up primarily of water, and together they make up about a foot of our adult height. Now, when you're standing upright, your spine supports the weight of your head, trunk, and upper body. All that pressure causes water to diffuse out of the intervertebral disks. Over the course of a day, you can loose up to an inch of your height due to intervertebral disk compression. Then, at night, when you're lying down, the water diffuses back into the disks and elongates your spine, so that when you wake up, it's ready to face another day.
This diffusion of water in and out of our intervertebral disks is also important because these disks aren't hooked up to our blood supply. This means that the water pumping in and out of them also provides them with nutrients and enables them to eliminate waste products. If you've ever wished you were just a little bit taller, try measuring your height in the morning. It might make all the difference.