A Close Look at Cholesterol
A Close Look at Cholesterol
January 27, 2023
Joy Stepinski, MSN, RN-BC
The public is constantly informed to keep cholesterol levels low. High cholesterol is a big risk factor for cardiac disease, the leading cause of death in the United States. Yet what is its purpose in the first place? Cholesterol does have benefit and a role in the body, and in fact is vital for life [1]. The molecule plays a role in the structure of the cell membranes and is important for its fluidity. Furthermore, the building of vitamins and hormones depend on cholesterol. Vitamin D, steroid hormones, and sex hormones are derived from it. Finally, bile salt contains cholesterol. Bile salt is found during digestion, and is needed by the body to absorb vitamins that dissolve in fat.
So how do the LDL and HDL cholesterol come into play? LDL cholesterol is commonly known as the “bad cholesterol,” while HDL cholesterol is known as “good.” These are formally known as low-density and high-density lipoproteins, which serve as cholesterol transporters. They are made of a protein membrane that surrounds a lipid (fat) center. LDL carries the cholesterol into the tissue, while HDL carries cholesterol from circulation to the liver where it is processed. LDL is considered “bad” because of this role, and is associated with the plaque that builds up in the arteries that can lead to disease, including heart attacks and stroke.
A fine balance is needed. The body requires cholesterol, yet too much puts stress on the cardiovascular system, and is a large risk factor for cardiovascular disease. When an excessive quantity of LDL exists in the body, atherosclerotic plaques can occur in the arteries. The lining of the arteries is called the endothelium. The endothelial lining allows cholesterol to enter through the artery wall. When too much LDL is present, the lining can become damaged and the amount of LDL that travels into the cell increases. Consequently, an inflammatory response occurs. Lipoproteins accumulate in the blood vessel wall, which attract certain white blood cells. The action of the white blood cells (specifically, macrophages) lead to the formation of foam cells, named for its appearance as soap bubbles [2]. The foam cell gives the fatty streak appearance of the plaque [3].
The body makes all the cholesterol it needs by the liver [4]. The rest comes from an unhealthy lifestyle: unhealthy diet, physical inactivity, tobacco exposure, and obesity. What about genetic predisposition? Often high cholesterol is blamed as a familial trait. One study [5] used three large cohorts and one cross-sectional analysis to investigate the effect of a healthy lifestyle on genetic risk. A total of 55,685 subjects were used. The study used a scoring system with the following measures: current smoking status, weight, physical activity, and healthy diet. The genetic risk factor was also determined. A high score was earned with no smoking; BMI <30; physical activity once weekly, and a dietary pattern of fruits, vegetables, nuts, whole grains, fish, and dairy products. The authors defined an unhealthy diet containing refined grains, processed meats, unprocessed read meats, trans-fats, sodium, and sugary beverages.
Subjects were classified according to genetic risk (high, medium, and low) and favorable lifestyle (high, medium, and low). The results found that even among people with a high genetic risk, which appeared to be independent of other factors, optimal lifestyle was associated with a reduction of coronary artery disease [5]. Higher coronary events occurred in the subjects who engaged in an unhealthier lifestyle. Comparably, participants with a low genetic risk were at greater risk of coronary events with an unhealthy lifestyle. Although patients may perceive that a lack of control to improve their outcomes with a high genetic risk, this study brings insight into showing that lifestyle factors can deeply affect health outcomes.
References
1. Huff, T., Boyd, B., & Jialal, I. (2022). Physiology, cholesterol. StatPearls [Internet]. https://www.ncbi.nlm.nih.gov/books/NBK470561/
2. Rader, D. J., & Puré, E. (2005). Lipoproteins, macrophage function, and atherosclerosis: beyond the foam cell?. Cell Metabolism, 1(4), 223-230. https://doi.org/10.1016/j.cmet.2005.03.005
3. Maguire, E. M., Pearce, S. W., & Xiao, Q. (2019). Foam cell formation: A new target for fighting atherosclerosis and cardiovascular disease. Vascular Pharmacology, 112, 54-71. https://doi.org/10.1016/j.vph.2018.08.002
4. American Heart Association. (2023). What is cholesterol? https://www.heart.org/en/health-topics/cholesterol/about-cholesterol
5. Khera, A. V., Emdin, C. A., Drake, I., Natarajan, P., Bick, A. G., Cook, N. R., ... & Kathiresan, S. (2016). Genetic risk, adherence to a healthy lifestyle, and coronary disease. New England Journal of Medicine, 375(24), 2349-2358. 1. https://doi.org/10.1056/NEJMoa1605086