Many theories of why humans require sleep are related to the brain. It's possible that our brain needs time to rest or reorganize the information it's acquired during the day. However, there's no denying that sleep plays an important role in our physical health as well.
They don't call it beauty sleep for nothing, as anyone who's woken up with dark under-eye circles and sallow skin can attest. During certain parts of the sleep cycle, your body turns into a repairman of sorts and releases growth hormones. The growth hormones set to work fixing damaged tissues, including the skin. If you don't get enough sleep, not only do you shortchange yourself on the growth hormone, you're also at risk for boosted levels of stress hormones, which can wreak havoc on your skin and age it prematurely.
If your idea of health and beauty is the ability to fit into your favorite pair of jeans, you might be interested to learn that sleep deficiency has been linked to obesity. Sleep is an important part of any healthy diet, because a lack of it affects hormones that control appetite. Sleep deprivation appears to decrease the amount of leptin and increase the amount of ghrelin in the body. When everything is working correctly, leptin is the hormone that tells your brain that you're full and can stop eating, while ghrelin alerts the brain when you're hungry and need to eat. Reversing those levels means that you'll always feel hungry, and your brain won't get the message that you're full.
Beauty sleep is more than skin-deep, though. Until fashion magazines start celebrating the puffy eyes, runny noses and feverish look that comes with a cold or flu, you'll want to stock up on sleep because it boosts your immune system. Sleep fends off other illnesses and diseases as well; a lack of sleep has been linked with conditions such as heart attack, diabetes, stroke and cancer.
Health problems are stressful enough; find out what happens when you add more stress on top of that on the next page.