Cholesterol, a yellowish fatty substance, is one of the essential ingredients of the body. Cholesterol is a building block of the outer membrane of cells. It is the principal ingredient of the digestive juice bile (needed to metabolise fat), in the fatty sheaths that insulate nerves and in sex hormones.  It performs several functions in the body.The amount of cholesterol is measured in milligrams per 100 millimeters of blood. Normal level of cholesterol varies between 150- 250 mg. per 100 ml. Though a useful substance in the body, excess cholesterol is harmful.In blood, cholesterol is bound to certain proteins - lipoproteins which have an affinity for blood fats, known as lipids. There are two main types of lipoproteins: a low density one (LDL) and a high density one (HDL). The low density lipoprotein is the one which is harmful and increases risk of heart diseases. While high density lipoproteins (HDL) are useful. Higher levels of HDL minimize the risk of heart problems.Excess of cholesterol in the body can accelerate the deposition of fat over the inner lining of blood vessels. This causes their occlusion in variable degree, thus impeding free flow of blood and necessary oxygen (carried by blood) to various body parts. Total obliteration of the coronary (bringing blood to heart) vessels can lead to heart attacks, while blockage of blood flow to the brain can result in stroke. A small clot can break from the fat deposit over the blood vessels and pass to the brain or lung causing serious problems of embolism. Impaired blood supply to the limbs can lead to one having painful cramps while working or walking.Apart from this, one is also at the risk of having high blood pressure due to occlusion of the vessels by fat. It is mostly saturated fats in the diet which lead to elevated cholesterol levels. Intake of fried foods, cheese, margarine, cream and butter, eggs, meat products except fish, all increase the risk of high cholesterol levels in the body.Lack of exercise also leads to obesity and high cholesterol levels in the body. Alcohol and cigarette smoking further contribute to the process.  Physical and mental stress release hormones which tend to increase the blood cholesterol levels. Apart from all these factors, in some people high cholesterol levels are inherited via genes.Some middle aged persons, mainly women have orange, yellow pigmentation around eyes, suggestive of high blood cholesterol. In elderly people, it may manifest as whitish ring around the eye ball. But apart from this, there are no marked features suggestive of high blood cholesterol.Diagnosis of high cholesterol levels is made by a simple blood test. It is done ideally without food in the morning so that food taken does not influence the results. If a lipid profile is ordered by the doctor, it includes the total cholesterol as well as high and low density lipoproteins and total triglycerides (another component of fats in the blood).To prevent high cholesterol levels and its attendant problems, one should avoid taking foods with high amount of fats. Intake of plenty of fresh vegetables and fruits, whole grains, nuts and fish helps in keeping blood cholesterol levels within normal limits. If habituated, one should try to quit alcohol and smoking. This will prevent rise in blood cholesterol and also help in avoiding other health related problems. Regular physical exercise is very useful to burn the extra calories consumed and helps to keep blood cholesterol within normal range. One should get tested for blood cholesterol after 40 years or so, at least once in a year. Because, with increasing age, process of atherosclerosis (fat deposited over inner lining of blood vessels) becomes advanced enough in the body to cause problems.If the blood cholesterol is high in spite of preventive measures, there is a need to take cholesterol lowering drugs like statins. These drugs are taken under medical supervision and can be stopped after the levels come to normal. As more people become aware of the harmful effects of high blood cholesterol, many related problems can be prevented or minimized.