Cholesterol is a fatty substance present in all cells of the body. Although too much cholesterol in the blood contributes to medical conditions, for example by increasing the risk for heart disease, cells in the body require cholesterol to produce hormones, make vitamin D and create bile, which aids in digestion. Therefore doctors set limits for normal, high and low for the different types of cholesterol to help people take steps to maintain healthy levels.
Types of Cholesterol
In order for cholesterol, a fatty substance, to move through the blood, which contains water, it must bind to a lipoprotein -- a specialized kind of protein. Two different lipoproteins bind cholesterol; low-density lipoprotein, known as LDL, and high-density lipoprotein, known as HDL. When testing a sample of blood for cholesterol, doctors report the total cholesterol level, a number that reflects the LDL and HDL together. The National Heart Lung and Blood Institute reports that total blood cholesterol should remain under 200 mg/dL for optimal health.
LDL Normal Limits
LDL binds cholesterol and carries it to the cells throughout the body. Excess cholesterol binds to LDL and remains in the bloodstream where it can accumulate along the walls of blood vessels, forming a substance called plaque. The formation of plaque restricts the flow of blood and increases the risk of heart disease, according to the American Heart Association. Doctors refer to LDL as the "bad" cholesterol because of its negative effects on the body. You should strive to keep your LDL levels low; less than 100 mg/dL is optimal, with 129 mg/dL the upper limit of normal.
LDL High Limits
As LDL levels become higher, more plaque forms, further restricting the flow of blood. Patients with LDL cholesterol values of 130 to 159 mg/dL border on the high limits. Doctors consider people with between 160 and 189 mg/dL in the high range and at risk for heart disease. Over 190 mg/dL exceeds the high limits and requires immediate attention to avoid additional health problems.
Effects of HDL
Although doctors often focus on lowering the levels of LDL to help maintain a healthy heart and healthy blood vessels, the amount of HDL also affects the body. HDL binds cholesterol and carries it to the liver for removal from the body. This means HDL helps protect the body from the harmful effects of excess cholesterol, making it the "good" cholesterol. Doctors therefore recommend increasing levels of HDL, keeping it above the lower limit of 40 mg/dL to counteract the effects of LDL.
Effects of Lifestyle Choices
Although only 25 percent of the cholesterol in the body comes from food, according to the American Heart Association, making healthy lifestyle choices affects the cholesterol levels in the blood. Eating a diet low in saturated and trans fats helps to keep LDL levels below the high limits while also increasing the levels of HDL. Avoid smoking, participate in plenty of physical activity and consume only moderate amounts of alcohol to help maintain healthy cholesterol levels.
