Cholesterol is an essential nutrient for human health that saves lives. It helps to protect against infectious disease and repairs damaged tissue. Cholesterol is naturally present in cell walls or membranes everywhere in the body, including the brain, nerves, muscles, skin, liver, intestines, and heart. Cholesterol is required in the membrane of mammalian cells for normal cellular function, and is either synthesized in the endoplasmic reticulum, or derived from the diet, in which case it is delivered by the bloodstream in low-density lipoproteins. Cholesterol can also be converted to vitamin D in our body and used for the calcification of bones and teeth. The precise causes of a high level of blood cholesterol are very complex, with many genetic factors playing important roles. The causes which are now seen as contributing to higher-than-normal cholesterol levels are: hereditary factors, which are the most important; then high blood pressure; followed by stress, smoking, obesity and dietary cholesterol. Unfortunately, some individuals have very high cholesterol levels, and the cause is hereditary; about 25 people in 10,000 carry this trait. Some drugs that are known to increase cholesterol levels include anabolic steroids, beta blockers, epinephrine, oral contraceptives, and vitamin D. Some studies have shown that fish oil supplementation may increase the level of LDL-cholesterol (the "bad" kind), but that the ratio of HDL-cholesterol (the "good" kind) to LDL remains unchanged. Another study found an average reduction of 38% in triglyceride levels and an increase of HDL levels of 24% in both men and women consuming fish on a daily basis. Healthy lifestyle changes such as losing excess weight and exercising regularly can help lower triglyceride levels. Physical fitness is to the human body what fine tuning is to an engine. Physical fitness is the capacity of the heart, blood vessels, lungs, and muscles to function at optimum efficiency. In previous years, fitness was defined as the capacity to carry out the day's activities without undue fatigue. Physical fitness is now defined as the body's ability to function efficiently and effectively in work and leisure activities, to be healthy, to resist hypokinetic diseases, and to meet emergency situations. Whether exercise is aerobic or anaerobic, exercise, health, and physical fitness go together for life. Aerobic fitness reduces brain tissue loss in aging humans. The decision to carry out a physical fitness program cannot be taken lightly. Unless you are convinced of the benefits of fitness and the risks of unfitness, you will not succeed. As you undertake your fitness program, it's important to remember that fitness is an individual quality that varies from person to person. Your goals, your present fitness level, age, health, skills, interest and convenience are among the factors you should consider. Exercise that doesn't raise your heart rate to a certain level and keep it there for 20 minutes won't contribute significantly to cardiovascular fitness. The best-laid plans of many a fitness program have been ruined by too much enthusiasm on the first day andsore muscles on the second. An aerobic exercise program can burn fat and increase the metabolic rate. Popular aerobic conditioning activities include brisk walking, jogging, swimming, cycling, rope-jumping, rowing, cross-country skiing, and some continuous action games like racquetball and handball. It is generally recommended that aerobic exercises be done three to five days per week, from twenty to sixty minutes of continuous activity at a time, such that the heart rate increases from 50 to 90 percent, depending on the intensity of the workout. Heart rate is widely accepted as a good method for measuring intensity during running, swimming, cycling and other aerobic activities. In a nation of couch potatoes, suggesting that people find whatever kind of exercise works for them is sound health advice. Weight training exercise is essential for enhancing muscular strength and endurance, helping to prevent the decline of muscle mass (and metabolic rate) that accompanies aging, and promoting bone health.
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