Q&A: What Do My Cholesterol Levels Mean?

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Question: I had my cholesterol checked, and I got four numbers back. Which one is most important, and what do the numbers mean with regard to my health?

Focus on cholesterolImage credit: Focus on cholesterol via Shutterstock

Answer: Cholesterol is a fatty molecule that is quite common in nature. While it has a bad nutritional reputation, it’s actually critical to normal cellular function. Cholesterol is the chemical precursor for the steroid hormones — estrogen, progesterone, and testosterone among them — and is converted into vitamin D in the skin cells with the help of sunlight. Furthermore, cholesterol helps cells maintain their membranes at the appropriate level of fluidity; too much cholesterol makes cell membranes stiff, but too little makes them overly fluid and weak.

While the body needs an appropriate amount of cholesterol in the cells to maintain normal function, too much cholesterol leads to heart disease. This is because cholesterol in excess of cellular needs builds up in the bloodstream, and eventually forms fatty deposits on the interior walls of arteries. This clogs the arteries and limits blood flow. Over time, it also hardens and weakens the arterial walls, which is known as atherosclerosis. Clogged arteries and atherosclerosis increase the risk of heart attack and stroke.

Perhaps the most confusing issue associated with understanding cholesterol numbers is that there are two “types” of cholesterol in colloquial parlance. These are referred to as “good” and “bad” cholesterol. From a stricter scientific perspective, however, these “types” of cholesterol are actually types of cholesterol transporter particles. What’s commonly called “bad cholesterol” is LDL, or low-density lipoprotein. This is a transporter particle that carries cholesterol from the liver to the body cells for uptake. High levels of LDL are associated with increased risk of atherosclerosis, heart attack and stroke. What’s commonly called “good cholesterol” is HDL, or high-density lipoprotein. HDL is a cholesterol transporter that carries cholesterol molecules from the body cells to the liver, which excretes them. High levels of HDL are associated with reduced risk of heart disease. Simply stated, the cholesterol molecules transported by LDL and HDL are identical; the major functional difference between the particles is the direction in which they carry cholesterol.

When healthcare professionals check a patient’s cholesterol, they are interested in three values. The first is LDL level, which should ideally be lower than 100 mg/dL. The second is HDL level, which should be higher than 60 mg/dL. HDL levels lower than 40 mg/dL for men (or 50 mg/dL for women) are indicative of greatly increased risk of heart disease. The third number is the triglyceride level, which should ideally be lower than 150 mg/dL. Triglycerides are fats in the bloodstream, and increase the risk of heart disease. Total cholesterol is calculated as LDL + HDL + one-fifth of triglycerides, and the American Heart Association recommends that it be less than 200 mg/dL. However, the caveat to this is that the breakdown of cholesterol levels by type provides much more information than the total cholesterol count. For instance, consider two scenarios:

Patient A has an LDL of 120 mg/dL, an HDL of 30 mg/dL, and a triglyceride level of 150 mg/dL. His total cholesterol is 120 mg/dL + 30 mg/dL + 30 mg/dL = 180 mg/dL. From glancing at the total cholesterol, the patient might assume that his risk of heart disease is low. By looking at the individual numbers, however, it’s clear that his risk is rather high. His LDL is above optimal, and his HDL is so low as to be a major risk factor.

Patient B has an LDL of 70 mg/dL, and HDL of 120 mg/dL, and a triglyceride level of 120 mg/dL. Her total cholesterol is 70 mg/dL + 120 mg/dL + 24 mg/dL = 214 mg/dL. This total cholesterol count ostensibly puts her in a higher risk category for heart disease, but by looking at the individual numbers, it becomes clear that her risk is actually quite low. Her LDL and triglycerides are well within the optimal range, and her HDL is exceedingly high, which is very cardioprotective.

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About the Author

Kirstin Hendrickson, Ph.D., is a science journalist and faculty in the Department of Chemistry and Biochemistry at Arizona State University. She has a PhD in Chemistry, and studied mechanisms of damage to DNA during her graduate career. Kirstin also holds degrees in Zoology and Psychology. Currently, both in her teaching and in her writing, she’s interested in methods of communicating about science, and in the reciprocal relationship between science and society. She has written a textbook called Chemistry In The World, which focuses on the ways in which chemistry affects everyday life, and the ways in which humans affect each other and the environment through chemistry.