What is cholesterol?
Cholesterol in the body is a waxy, fat-like substance found in cell walls that come from two sources: the body and the food we eat. The body, especially the liver, makes all the cholesterol it needs, and this is used to make essential substances like hormones and bile acids. Bile acids facilitate digestion and absorption of lipids in the small intestine.
Cholesterol circulates in the blood throughout the body and is transmitted through the blood plasma. The body uses it to form cell membranes and hormones; it is a fundamental part of the structural component of human cell membranes.
Why is cholesterol important?
Cholesterol is essential for the body because it produces bile acid, vitamin D, and steroid hormones. However, excessive cholesterol in the blood may be harmful.
Cholesterol is recycled by way of being first excreted by the liver through the bile, from which it then goes into the digestive tract. Almost half of all excreted cholesterol is reabsorbed into the bloodstream courtesy of the small bowel.
Understanding cholesterol levels
The National Institutes of Health (NIH) recommends everyone over the age of 20 have their cholesterol checked once every five years. A majority of cardiologists recommend a fast of 12 hours before a cholesterol test because triglycerides can shoot up 20%–30% after a meal. Alcohol will also cause a triglyceride surge.
The blood test, lipoprotein profile, or lipid panel, provides the following:
- Total cholesterol
- LDL “bad” cholesterol—the main source of cholesterol buildup and blockage in the arteries (makes up 60%–70% of total cholesterol)
- HDL “good” cholesterol—transports excessive cholesterol away from the arteries to the liver—helps protect against heart disease; it keeps cholesterol from building up in the arteries (makes up 20%–30% of total cholesterol)
- Triglycerides—another form of fat in the blood—triglycerides have been associated with the onset of atherosclerosis, deposits of plaque on the inside walls of the arteries.
Very low-density lipoprotein, or VLDL, makes up 10%–15% of total cholesterol. It is a known kind of lipoprotein manufactured by the liver and is a precursor of LDL. The purpose of VLDL is to move cholesterol and other lipids through the bloodstream. VLDL is regarded as the human body’s internal transmission system for lipids.
The LDL is calculated by plugging the measurements for total cholesterol, HDL, and triglycerides into an equation: Total cholesterol — HDL — (Triglycerides ÷ 5) = LDL.
LDL can also be measured directly in a non-fasting blood sample, as when triglycerides exceed 300 mg/dL (3.36 mmol/L)—when triglycerides are this high, the calculation will not be accurate.
A cholesterol ratio is often used to assess a person’s risk for heart disease. The HDL number is divided into the total cholesterol number. An optimal ratio is reported as less than 3.5-to-1. A higher ratio means a higher risk of heart disease.
Cholesterol levels are measured in milligrams (mg) of cholesterol per deciliter (dL) of blood. A full lipoprotein profile needs to be completed if the total cholesterol is greater than 200 mg/dL or if the HDL is less than 40 mg/dL. Table 1 shows the total cholesterol level in relation to its category and Table 2 displays LDL level in relation to its category.
Total cholesterol level and category
Total cholesterol level Category Less than 200 mg/dL Desirable 200–239 mg/dL Borderline high 240 mg/dL and above High
Note. Retrieved from the NIH.
LDL cholesterol level and category
LDL cholesterol level LDL-cholesterol category Less than 100 mg/dL Optimal 100–129 mg/dL Near optimal/above optimal 130–159 mg/dL Borderline high 160–189 mg/dL High 190 mg/dL and above Very high
Note. Retrieved from the NIH.
If outside of the U.S. take the U.S. mg/dL limits for all the numbers and divided by 38.66, which is the conversion factor. A U.S. cholesterol number of 200 mg/dL is the same as a SI (International System of Units) cholesterol number of 200/38.66 = 5.17 mmol/L.
What affects cholesterol levels?
Many factors can affect cholesterol levels.
Age and gender —Cholesterol levels rise as men and women age. After the age of menopause, women’s LDL levels tend to increase, which raises the total cholesterol level. Children can have high cholesterol; however, it is not as prevalent in children.
Heredity—Genes, to a certain degree, determine how much cholesterol the body makes.
Race or ethnic group—explained in Table 3
Cholesterol levels vary by race
Racial or ethnic group Men (%) Women (%) Non-Hispanic Blacks 30.7 33.6 Mexican Americans 38.8 31.8 Non-Hispanic Whites 29.4 32.0 All 31.0 32.0
Note. Table retrieved from the CDC.
Diet—Saturated fat and cholesterol in food can make blood cholesterol levels go up. Reducing the amount of saturated fat and cholesterol in the diet helps lower blood cholesterol levels. Dietary cholesterol is found in foods from animal sources, such as meat, dairy, egg yolks. The liver will produce more cholesterol when consuming a diet high in saturated and trans fats. Interestingly, the NIH reports,
“…that there was not enough evidence across a broad range of dietary cholesterol intake to make a recommendation regarding dietary cholesterol for treatment of high levels of LDL cholesterol.”
Weight—Being overweight tends to increase cholesterol. Losing weight can help lower LDL and total cholesterol levels, as well as increase HDL. Losing weight will also decrease triglycerides.
Physical activity—Regular physical activity helps lower LDL and raise HDL levels.
Vitamin D—Because vitamin D is synthesized from cholesterol, researchers show interest in exploring its potential role in cholesterol regulation.
Cholesterol levels and heart disease
High blood cholesterol, or hyperlipidemia, is prevalent in America and is one of the major risk factors for developing heart disease; therefore, it is crucial to monitor cholesterol levels along with assessing other risk factors.
Heart disease and damaged arteries are associated with high cholesterol, but having high cholesterol doesn’t necessarily mean a person will develop heart disease. Risk factors for heart disease include:
- Cigarette smoking
- High blood pressure (140/90 mmHg or higher)
- Low HDL cholesterol (less than 40 mg/dL)
- Family history
- Women 55 years or older; men 45 years or older
The NIH explains that the more risk factors a person has, the greater the chances are of developing heart disease or having a heart attack. Some people are at high risk because they already have heart disease and other people are at high risk for developing heart disease because of a combination of risk factors.
Low cholesterol, or hypolipidemia, is better than high cholesterol most of the time, such as when taking cholesterol-lowering agents, such as statins, to lower high cholesterol.
It is when the cholesterol level drops for no apparent reason that is of concern. Further research is needed in the area of low cholesterol because cholesterol is vital for the production of hormones and brain function.
While high cholesterol can be a daunting issue for a person, there are many healthy benefits in trying to stave off out-of-control cholesterol levels. Having the right mix of attitude and determination can do a great deal to ensure that cholesterol levels do not get too high.
For example, one can engage in a certain amount of cardiovascular exercise a few times a week, such as walking or running for up to 30 minutes, which really makes a difference in keeping high levels of bad cholesterol at bay. Additional good advice is to eat a balanced diet with lean meat, vegetables, whole-grains, and fruits and avoid processed foods and sugar.
What is Cholesterol: https://www.nhlbi.nih.gov/health/health-topics/topics/hbc
Questions and Answers on Cholesterol and Health with NHLBI Nutritionist Janet de Jesus, M.S., R.D.: https://www.nhlbi.nih.gov/news/spotlight/fact-sheet/questions-and-answers-cholesterol-and-health-nhlbi-nutritionist-janet-de-jesus-ms-rd
Bile Acids and Metabolic Regulations: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2811459/
Millan J. et al. . Lipoprotein ratios: Physiological significance and clinical usefulness in cardiovascular prevention. Vascular health and risk management 5, 757–765 (2009). Retrieved from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5341156/
High Cholesterol Facts: https://www.cdc.gov/cholesterol/facts.htm
Information on the Development of the 2015 Dietary Guidelines for Americans: https://health.gov/sites/default/files/2019-09/2015-2020_Dietary_Guidelines.pdf
What is Metabolic Syndrome: https://www.nhlbi.nih.gov/health/health-topics/topics/ms
High Blood Cholesterol: What You Need to Know: https://www.nhlbi.nih.gov/health/resources/heart/heart-cholesterol-hbc-what-html
Medline Plus Cholesterol Information: https://medlineplus.gov/cholesterol.html