Structure of HDL
HDL is the smallest of the lipoproteins. They are the densest because they contain the highest proportion of protein. The liver synthesises these lipoproteins as empty flattened spherical protein particles. They are capable of picking up cholesterol, carried internally, from cells they interact with. They increase in size as they circulate through the bloodstream. Thus it is the concentration of large high density lipoprotein particles which more accurately reflect protective action, as opposed to the concentration of total high density lipoproteins particles. This ratio of large high density lipoproteins to total HDL particles varies widely and is only measured by more sophisticated lipoprotein assays using either electrophoresis, the original method developed in the 1970s, or newer NMR spectroscopy methods, developed in the 1990s.
Men tend to have noticeably lower HDL levels, with smaller size & lower cholesterol content, than women. Men also have an increased incidence of atherosclerotic heart disease. Epidemiological studies have shown that high concentrations of HDLs (over 60 mg/dL) have protective value against cardiovascular diseases (such as ischemic stroke and myocardial infarction).