Cholesterol is a necessary component in the production of several important hormones, including cortisol, which modulates the stress response; aldosterone, which regulates water balance in the body; and the sex hormones estrogen, progesterone and testosterone. Cholesterol is also used in the digestive system to form bile, which breaks down fats and makes them more digestible, and in turn makes the fat-soluble vitamins A, D, E and K more absorbable. Excess cholesterol is implicated in the high rates of cardiovascular disease; however, insufficient cholesterol also poses serious health risks.
Immunity
Low cholesterol levels were shown to impair an HIV treatment known as highly active antiretroviral therapy, in a study published in the 2010 "Journal of the International AIDS Society." The researchers found that cholesterol's immunomodulary properties interact with the drug therapy. The study measured viral-immune status over 24 weeks of highly active antiretroviral therapy. At baseline, the hypocholestrolemic patients -- those with cholesterol levels of less than 150 mg/dl -- had lower CD4 immune cell levels and more prevalence of detectable virus. After highly active retroviral therapy, participants with low cholesterol had twice the drug failure rate of those without low cholesterol levels. The researchers also report that for every 50 mg/dl rise in cholesterol, the CD4 count was restored by 50 cells.
Critical Care
Very low cholesterol levels are often found concurrently with critical illness, such as multiple traumas, extensive surgery or major infection, according to a meta-analysis published in the 2008 "Biomedical Papers of the Medical Faculty of the University of Palacky, Olomouc Czech Republic." The study examined the role of cholesterol during the stressful period of intensive care. The researchers reported that low cholesterol levels were associated with higher incidence of post-operative infections, and in one large hospital study were associated with a ten-fold increase in mortality. The study cites an important function of cholesterol in neutralizing endotoxins -- components of certain bacteria that cause an immune system response -- as one of the potential mechanisms of importance in the relationship between cholesterol and immunity in the critical care setting.
Artery Plaque Formation
One of the initial phases of plaque formation, which narrows arteries and can lead to heart attacks and strokes, involves a process whereby certain immune cells, known as macrophages, absorb cholesterol and undergo degeneration into a form known as foam cells. Foam cells accumulate in the linings of arteries and cause further accumulation of platelets and other components of blood, eventually forming an atheroma, or plaque, within the artery. A study published in 2008 in "Circulation Research" reported that foam cells formed in mice in the presence of low cholesterol levels, implying that cholesterol is not the instigator of atherogenesis that it is widely believed to be. In the study, mice with severely low cholesterol had massive foam cell formation but no lipid accumulation in the walls of their arteries. This experiment suggests that controlling cholesterol levels may not be the most important factor in preventing arterial plaque formation since foam cell formation and subsequent plaque formation can occur without elevated cholesterol.
References
- PubMed.gov: Low cholesterol? Don't brag yet ... hypocholesterolemia blunts HAART effectiveness: a longitudinal study
- PubLib: Hypocholesterolemia in Clinically Serious Conditions
- Circulation Research: Coexistence of Foam Cells and Hypocholesterolemia in Mice Lacking the ABC Transporters A1 and G1
- Textbook of Bacteriology: Bacterial Endotoxin
- Virginia.edu: Macrophage Differentiation to Foam Cells
