From VOA Learning English, this is the Health & Lifestyle report.

　　We spend about one-third of our lives asleep. This may sound like a lot of time, but it is not wasted.

　　Our bodies need sleep to stay healthy. Not getting enough sleep, or as we sometimes say shut-eye, can make us sick.

　　Sleep and our immune system

　　The immune system protects the body from diseases and infections. Not getting enough sleep hurts this protective system.

　　The Mayo Clinic is a nonprofit research hospital in the United States. Its website explains that when we sleep our bodies release proteins that support sleep and help us fight infections. They add that infection-fighting antibodies and cells are reduced during periods when you don't get enough sleep.

　　A new study from the University of Washington in the U.S. seems to confirm this. Dr. Nathaniel Watson was the lead writer of the study. He is also co-director of the university's Medicine Sleep Center at Harborview Medical Center.

　　Watson says his study shows that the immune system works best when the body gets enough sleep.

　　For the study, Watson and his team studied 11 pairs of identical twins. This is an important difference from other sleep studies. Other research did not study identical twins.

　　The identical twins, however, had different sleep patterns. Researchers found that the twin who slept less had a weaker immune system.

　　Watson says his study showed for the first time that a long-term lack of sleep shuts down parts of the immune system. He says parts that move white blood cells around the body are affected. White blood cells fight infection in the body.

　　Watson adds that the results confirm a finding of other sleep studies. They found that when sleep-deprived people are given a vaccine, fewer antibodies are produced. If sleep-deprived people are then exposed to a virus, he says, "they are more likely to get the virus."

　　Watson's study provides more evidence that sleep is important to "overall health and well-being." And sleep is especially important to immune health.

　　The researchers published their findings in the journal Sleep.

　　How much sleep is enough?

　　To stay in good health, experts at the Mayo Clinic say that adults should get seven to eight hours of sleep. Teenagers need nine to 10 hours. And school-aged children may need more than 10 hours of sleep a night.

　　Experts say the quality and quantity of our sleep becomes poor as we age. This happens because brain circuits that control sleep slowly begin to weaken.

　　Experts say the process begins in our 30s. By the time we reach our 50s, the average person has lost 50 percent of their ability to have a restful sleep.

　　These people also have trouble falling asleep and staying asleep through the night. From middle age on, they say these problems only get worse, and they can affect our health.

　　Signs you may not be getting enough sleep

　　The website Health.com lists several signs that may mean you are not getting enough sleep.

　　•You're always hungry or you've gained weight. A lack of sleep can affect the hormones that tell your brain you have eaten enough.

　　•You have trouble making decisions. A lack of sleep may affect your higher level brain functions, such as problem solving.

　　•You have trouble remembering things. Sleep helps prepare the brain for new memories.

　　•You feel very emotional. People who are sleep deprived may feel unable to control their emotions, whether they be angry, sad or happy.

　　•Your skin doesn't look good. When we sleep, the body repairs damaged cells, like skin cells. (We don't call it beauty sleep for nothing!)

　　•You are having trouble seeing. When you're tired you may not be able to control your eye muscles.

　　How to improve your sleep

　　There are things people can do get better sleep.

　　Health experts recommend exercise and avoiding work on computers and electronic devices before bed. A cool room is also a better environment for sleeping.

　　And that's the Health & Lifestyle report.

　　I'm Anna Matteo.

　　Jessica Berman reported this story for VOA News. Anna Matteo adapted it for Learning English. Mario Ritter was the editor.

　　What are your sleep habits? Do you think you're getting enough beauty sleep? Or could you use more shut-eye? Let us know in the Comments Section.