Cholesterol is a fatty substance that has strong links to cardiovascular disease, and adults are advised to have a cholesterol test to check whether their levels fall within the acceptable range. Cholesterol levels tend to stay fairly constant from day to day due to the complex mechanisms that control the levels in your blood. Long-term lifestyle changes and some medications are the only way to guarantee sustainable decreases in your cholesterol levels.
Definition
Cholesterol is a molecule produced in your body and present in some foods you eat. It is a fatty substance found in the highest quantities in foods such as red meat, liver, eggs and cheese. It is frequently branded as a dangerous chemical in the press, responsible for causing diseases such as strokes and heart attacks. Although excessive intake of cholesterol has been tied to an increased chance of developing cardiovascular conditions and should certainly be avoided, cholesterol is needed in small quantities to perform essential functions in your body.
Types of Cholesterol
Cholesterol is carried around your blood bound to certain proteins called lipoproteins. These can transport cholesterol to the liver, where they are removed from the body, a very normal process. However, there are two types of cholesterol-carrying proteins called low-density lipoprotein, or LDL, and high-density lipoprotein, or HDL. High levels of LDL have been tied to adverse health effects of cholesterol, while high levels of HDL seem to play a protective role.
Cholesterol Levels
When doing a cholesterol test, the doctor will be looking at how high your LDL levels are compared with your HDL, and how much total fat, or triglycerides, you have circulating in your blood. A combination of high triglycerides, low HDL and high LDL can indicate an increased risk of developing cardiovascular disease. According to the National Institutes of Health, the following levels are guidelines to follow when doing a cholesterol test: Total cholesterol less than 200 is considered low risk--above 240 mg/dL is considered high risk; an LDL less than 100 mg/dL is optimal, 130-159mg/dL is considered borderline high and above 190mg/dL is very high; and triglycerides less than 150mg/dL are normal--above 200mg is considered high to very high.
Cholesterol Tests
A cholesterol test is performed by taking a sample of your blood after 9 to 12 hours of fasting. This is important as the liver will remove cholesterol from your blood for 8 hours after a meal, and eating prior to the test may reduce the accuracy of the results. Researchers at the National Heart, Lung and Blood Institute found that people who break their fast before getting tested underestimated their LDL by approximately 4 percent and their triglyceride levels by 20mg/dL. This may not seem like much, but it will certainly seem more significant if your levels are borderline high.
Daily Variations in Cholesterol
The liver produces about 15 percent of the circulating cholesterol itself, and because of this, blood levels can be controlled by reducing or increasing synthesis. Cholesterol levels remain fairly constant during the day. As well as being able to synthesize cholesterol, the body reabsorbs much of the excreted cholesterol in the small intestine, resulting in a finely balanced mechanism that controls blood cholesterol. A 2009 study by PM Clifton and colleagues, published in the "American Journal of Clinical Nutrition," showed that giving subjects a high dose of cholesterol during a meal had no significant effect on LDL levels after the meal.
Accuracy of Cholesterol Tests
The ability to judge cholesterol levels depends heavily on the accuracy of the tests that are employed. It has been known since the early 1930s that cholesterol measurements are strongly influenced by the surrounding temperature and that variations of 15 percent can occur within an individual's test outcome if the test is taken under different temperature conditions. Even if the same tests are used, there can be other reasons for variations. For example, seasonal variations have been reported, with one 2004 study in the "Archives of Internal Medicine" reporting that 22 percent more adults had cholesterol levels much higher in the winter than the summer months, although the reasons for this are unknown.
Reducing Cholesterol
Cholesterol is therefore unlikely to vary much from day to day, although fasting is recommended before a test to ensure more accurate results. Reducing overall cholesterol intake in the long run is much more effective at reducing cholesterol levels. A 2000 study in the "Journal of the American Medical Association" showed that by replacing butter with a low-cholesterol margarine, subjects experienced a drop in their cholesterol levels of 11 percent in just two weeks.
References
- National Cholesterol Education Program
- National Institutes of Health: Cholesterol Testing
- "Diurnal Variations of the Cholesterol Content of the Blood"; Maurice Bruger and Irving Somach; 1932
- "Archives of Internal Medicine"; "Seasonal Variations in Blood Cholesterol levels"; 2004
- Cholesterol Synthesis and Control
