Many of us try to sleep as little as possible—or feel like we have should. There are so many things that seem more interesting or important than getting a few more hours of sleep, but just as exercise and nutrition are essential for optimal health and happiness, so is sleep. The quality of your sleep directly affects the quality of your waking life, including your mental sharpness, productivity, emotional balance, creativity, physical vitality, and even your weight. No other activity delivers so many benefits with so little effort.

Sleep isn’t exactly a time when your body and brain shut off. While you rest, your brain stays busy, overseeing a wide variety of biological maintenance that keeps your body running in top condition, preparing you for the day ahead. Without enough hours of restorative sleep, you won’t be able to work, learn, create, and communicate at a level even close to your true potential. Regularly skimp on “service” and you’re headed for a major mental and physical breakdown.

The good news is that you don't have to choose between health and productivity. As you start getting the sleep you need, your energy and efficiency will go up. In fact, you're likely to find that you actually get more done during the day than when you were skimping on shuteye.


While we may not often think about why we sleep, most of us acknowledge at some level that sleep makes us feel better. We feel more alert, more energetic, happier, and better able to function following a good night of sleep. However, the fact that sleep makes us feel better and that going without sleep makes us feel worse only begins to explain why sleep might be necessary.

One way to think about the function of sleep is to compare it to another of our life-sustaining activities: eating. Hunger is a protective mechanism that has evolved to ensure that we consume the nutrients our bodies require to grow, repair tissues, and function properly. And although it is relatively easy to grasp the role that eating serves  given that it involves physically consuming the substances our bodies need eating and sleeping are not as different as they might seem.

Both eating and sleeping are regulated by powerful internal drives. Going without food produces the uncomfortable sensation of hunger, while going without sleep makes us feel overwhelmingly sleepy. And just as eating relieves hunger and ensures that we obtain the nutrients we need, sleeping relieves sleepiness and ensures that we obtain the sleep we need.

Scientists have explored the question of why we sleep from many different angles. They have examined, for example, what happens when humans or other animals are deprived of sleep. In other studies, they have looked at sleep patterns in a variety of organisms to see if similarities or differences among species might reveal something about sleep's functions. Yet, despite decades of research and many discoveries about other aspects of sleep, the question of why we sleep has been difficult to answer.


Research suggests that sleep plays an important role in memory, both before and after learning a new task.
Lack of adequate sleep affects mood, motivation, judgment, and our perception of events.
Although there are some open questions about the specific role of sleep in forming and storing memories, the general consensus is that consolidated sleep throughout a whole night is optimal for learning and memory.

Our bodies regulate sleep in much the same way that they regulate eating, drinking, and breathing. This suggests that sleep serves a similar critical role in our health and well-being.

Although it is difficult to answer the question, "Why do we sleep?" scientists have developed several theories that together may help explain why we spend a third of our lives sleeping.

Understanding these theories can help deepen our appreciation of the function of sleep in our lives.
It may seem obvious that sleep is beneficial. Even without fully grasping what sleep does for us, we know that going without sleep for too long makes us feel terrible, and that getting a good night's sleep can make us feel ready to take on the world.

Scientists have gone to great lengths to fully understand sleep's benefits. In studies of humans and other animals, they have discovered that sleep plays a critical role in immune function, metabolism, memory, learning, and other vital functions. The features in this section explore these discoveries and describe specific ways in which we all benefit from sleep.


Treatment of high blood cholesterol consists of first reducing the amount of saturated fat and cholesterol in the diet. Poultry and fish are low in cholesterol. Cereals, fresh fruit, and vegetables contain no cholesterol. Regular aerobic exercise--such as bicycling, running, and swimming--can further lower the cholesterol level. Medication should be considered only for people who are at high risk of heart disease and who have been unable to control their cholesterol with diet. Medications shown to reduce cholesterol levels and the risk of heart disease include cholestyramine, colestipol, gemfibrozil, lovastatin, and niacin.

Clinical research trials have indicated that lowering the amount of cholesterol in the blood can reduce the risk of heart attack in middle-aged men who had no history of heart disease. In men and women with atherosclerosis, reducing cholesterol in blood prevents further narrowing of the heart arteries.

High blood cholesterol is treated with lifestyle changes and medicines. The main goal of treatment is to lower your low-density lipoprotein (LDL) cholesterol level enough to reduce your risk for coronary heart disease, heart attack, and other related health problems.

Your risk for heart disease and heart attack goes up as your LDL cholesterol level rises and your number of heart disease risk factors increases.

Some people are at high risk for heart attacks because they already have heart disease. Other people are at high risk for heart disease because they have diabetesexternal link icon or more than one heart disease risk factor.

Talk with your doctor about lowering your cholesterol and your risk for heart disease. Also, check the list to find out whether you have risk factors that affect your LDL cholesterol goal:

  • Cigarette smoking
  • High blood pressure (140/90 mmHg or higher), or you’re on medicine to treat high blood pressure
  • Low high-density lipoprotein (HDL) cholesterol (less than 40 mg/dL)
  • Family history of early heart disease (heart disease in father or brother before age 55; heart disease in mother or sister before age 65)
  • Age (men 45 years or older; women 55 years or older)

You can use the NHLBI 10-Year Risk Calculatorexternal link icon to find your risk score. The score, given as a percentage, refers to your chance of having a heart attack in the next 10 years.


Drug therapy, also called chemotherapy, is used against a wide variety of cancers. Chemotherapy has proved especially effective in treating leukemia, lymphoma, and testicular cancer. Cancer cells divide much more rapidly than normal cells. Therefore, many cancer drugs are designed to interfere with cell division.

Chemotherapy causes side effects by injuring the normal body cells, especially those that divide most rapidly. Rapidly dividing normal cells include blood-forming cells, cells that line the intestines, and hair-forming cells. Damage to blood-forming cells may increase a patient's risk of developing anemia or an infection. Injury to intestinal cells may cause nausea and vomiting. Disruption of hair-forming cells can cause hair loss. Researchers work constantly to develop drugs that reduce harm to normal cells.

Effective chemotherapy usually involves combinations of drugs. Doctors combine drugs that have different methods of acting on cancer cells and that produce different side effects. Combination therapy reduces the chance that cancer cells will develop resistance to the drugs. It also helps avoid serious side effects from large doses of a single drug.

Treatment Methods

Questions to Ask Your Doctor About Treatment
Suggested questions for cancer patients to ask their doctors about treatment choices and the possible side effects of treatment.

Types of Treatment
Information on chemotherapy, radiation therapy, targeted therapies, and other cancer treatment methods.
Complementary and Alternative Medicine
Healing philosophies, approaches, and therapies used in complementary and alternative medicine (CAM) in cancer care.
Cancer Treatment Scams
Information from the Federal Trade Commission for cancer patients about how to spot false health claims and the importance of talking with their physicians about treatments they are considering.

Cancer Treatment Facilities

How To Find a Doctor or Treatment Facility If You Have Cancer
A fact sheet that offers suggestions for choosing a physician and facility for cancer treatment.
NCI-Designated Cancer Centers
NCI-Designated Cancer Centers develop and translate scientific knowledge from promising laboratory discoveries into new treatments for cancer patients. They are at the forefront of NCI-supported efforts at universities and cancer research centers across the United States. Find a center near you and learn about their research capabilities and patient services.
Cancer Clinical Trials at the NIH Clinical Center
A fact sheet about cancer clinical trials at the NIH Clinical Center in Bethesda, Maryland.


A variety of things can affect cholesterol levels. These are things you can do something about:

■ Diet. Saturated fat and cholesterol in the food you eat make your blood cholesterol level go up. Saturated fat is the main culprit, but cholesterol in foods also matters. Reducing the amount of saturated fat and cholesterol in your diet helps lower your blood cholesterol level.

■ Weight. Being overweight is a risk factor for heart disease. It also tends to increase your cholesterol. Losing weight can help lower your LDL and total cholesterol levels, as well as raise your HDL and lower your triglyceride levels.

■ Physical Activity. Not being physically active is a risk factor for heart disease. Regular physical activity can help lower LDL (bad) cholesterol and raise HDL (good) cholesterol levels. It also helps you lose weight. You should try to be physically active for 30 minutes on most, if not all, days.

Things you cannot do anything about also can affect cholesterol levels.
These include:
Age and Gender. As women and men get older, their cholesterol levels rise. Before the age of menopause, women have lower total cholesterol levels than men of the same age. After the age of menopause, women’s LDL levels tend to rise.
Heredity. Your genes partly determine how much cholesterol your body makes. High blood cholesterol can run in families.

In adults, a cholesterol level of less than 200 milligrams per 1 deciliter (3 ounces) of blood is considered desirable. Above that level, the risk of heart disease increases dramatically. Adults also are at an above-average risk of heart disease if they have an LDL-cholesterol level of more than 160 milligrams per deciliter of blood or an HDL-cholesterol level of less than 40 milligrams per deciliter.

Besides cholesterol levels, other factors increase the risk of heart disease. These factors include cigarette smoking, high blood pressure, diabetes, a family history of premature heart disease, and being a male over 44 years of age or a female over 54. Individuals with two or more of these factors have high risk of heart attack, particularly if they also have atherosclerosis (narrowing of the arteries because of fatty deposits).


The TLC Diet. This is a lowsaturated- fat, low-cholesterol eating plan that calls for less than 7 percent of calories from satrated fat and less than 200 mg of dietary cholesterol per day. The TLC diet recommends only enough calories to maintain a desirable weight and avoid weight gain. If your LDL is not lowered enough by reducing saturated fat and cholesterol intakes, the amount of soluble fiber in your diet can be increased. Certain food products that contain plant stanols or plant sterols (for example, cholesterollowering margarines) can also be added to the TLC diet to boost its LDL-lowering power.

Weight Management. Losing weight if you are overweight can help lower LDL and is especially important for those with a cluster of risk factors that includes high triglyceride and/or low HDL levels and being overweight with a large waist measurement (more than 40 inches for men and more than 35 inches for women).

 Physical Activity. Regular physical activity (30 minutes on most, if not all, days) is recommended for everyone. It can help raise HDL and lower LDL and is especially important for those with high triglyceride and/or low HDL levels who are overweight with a large waist measurement.

Complications of obesity. Obesity impairs the function of many organ systems in the body, such as the circulatory system. The risk of serious medical conditions increases with higher BMI values. In addition, obesity reduces quality of life, complicates recovery from surgery, and causes premature death. There is also discrimination against obese people. Obese people often have less social success than thinner people and find it harder to get jobs.

Effect of weight loss. Weight loss in obese people improves or eliminates obesity-related medical conditions and improves quality of life. Many of the results are directly related to the amount of weight lost. Beneficial health effects are even seen after modest weight losses and increase with greater weight loss. Obese people do not have to become lean to benefit from weight loss. Weight loss of as little as 10 percent of total body weight can produce significant health benefits, even in people who remain obese.