A desirable level of LDL (“bad”) cholesterol is less than 100 mg/dL – the lower your LDL, the better in terms of heart disease risk. Levels between 139 and 150 mg/dL are borderline high and those between 160 to 189 mg/dL are considered high, while LDL levels above 190 mg/dL are classed as very high. According to the American Heart Association, the mean level of LDL cholesterol for American adults age 20 and older is 115.0 mg/dL.
Plasma HDL is a small, spherical, dense lipid-protein complex that is half lipid and half protein. The lipid component consists of phospholipids, free cholesterol, cholesteryl esters, and triglycerides. The protein component includes apo A-I (molecular weight, 28,000) and apo A-II (molecular weight, 17,000). Other minor, but important, proteins are apo E and apo C, including apo C-I, apo C-II, and apo C-III.
However, although low levels of HDL predict increased cardiovascular risk, particularly in healthy individuals with no history of cardiovascular events, the relationship between HDL and CHD risk is complex, with HDL-C and cardiovascular disease having a nonlinear relationship. For example, research found that HDL levels above approximately 60 mg/dL showed no further improvement in prognosis, and the EPIC (European Prospective Investigation into Cancer and Nutrition)-Norfolk and IDEAL (Incremental Decrease in End Points through Aggressive Lipid Lowering) studies showed that very high levels of HDL may actually be associated with an increased risk of atherosclerotic disease. [5, 6, 2]
Hayek T, Chajek-Shaul T, Walsh A, Agellon LB, Moulin P, Tall AR, Breslow JL. An interaction between the human cholesteryl ester transfer protein (CETP) and apolipoprotein A-I genes in transgenic mice results in a profound CETP-mediated depression of high density lipoprotein cholesterol levels. J Clin Invest. 1992 Aug;90(2):505–510. [PMC free article] [PubMed]