Until today I knew that there were two different kinds of cholesterol, a “good” one (HDL) and a “bad” one (LDL).
What really mattered was to keep an eye on the latter, “The Bad Guy”, responsible for health problems and cardiovascular diseases. While the former could be considered “The Good Guy”, thanks to its ability to remove cholesterol from within artery atheroma and transport it back to the liver for excretion or re-utilization.
In other words - to be healthy - we needed more HDL and less LDL: easy as that!
Unfortunately, as it often happens, things are not as black and white as one would want (and hope) to believe. And, as a matter of fact, a new study by Harvard School of Public Health (HSPH), published online in the Journal of the American Heart Association, has found that there is a subclass of the "good" cholesterol (HDL), that does not protect against coronary heart disease and may, instead, be harmful.
This is the first study to show that a small protein (called apolipoprotein C-III or apoC-III) that sometimes resides on the surface of HDL cholesterol may increase the risk of heart disease.
In general terms, a high level of HDL cholesterol is strongly predictive of a low incidence of coronary heart disease (CHD).
However, trials of drugs that increase HDL cholesterol have not consistently shown decreases in CHD, leading to the hypothesis that HDL cholesterol may contain both protective and non-protective components.
ApoC-III, a proinflammatory protein secreted mostly by the liver and, to a lesser extent, by the intestine, resides on the surface of some lipoproteins both HDL and low-density lipoproteins, or LDL ("bad") cholesterol.
In this study the researchers - led by Frank Sacks, professor of cardiovascular disease prevention at HSPH and Majken Jensen, research associate in the Department of Nutrition at HSPH - examined whether the existence or absence of apoC-III on HDL cholesterol affected the "good" cholesterol's heart-protective qualities.
In addition, they tested whether its existence could differentiate HDL cholesterol into two subclasses: those which protect against the risk of future heart disease and those which do not.
The researchers collected more than 50,000 blood samples from both women and men in the early 90s. During the following 10 to 14 years of follow-up, 634 cases of coronary heart disease were documented and matched with controls for age, smoking, and date of blood drawing.
Their findings showed that the HDL cholesterol that had apoC-III present on its surface was associated with higher risk of coronary heart disease.
It should be noted, however, that only a small fraction (i.e., 13%) of HDL cholesterol had the proinflammatory protein on the surface.
Furthermore, the study confirmed that the major HDL type (which lacks the portein apoC-III) had the expected heart-protective association with coronary heart disease.
"This finding, if confirmed in ongoing studies, could lead to better evaluation of risk of heart disease in individuals and to more precise targeting of treatments to raise the protective HDL or lower the unfavorable HDL with apoC-III," said Sacks.
The results suggest that measuring HDL apoC-III and HDL without apoC-III rather than the simpler measure of total HDL may be a better gauge of heart disease risk (or of HDL's protective capacity). "Reduction in HDL-apoC-III by diet or drug treatments may become an indicator of efficacy," said Jensen.
While we’ll wait to get more details on how to address the issue of the HDL cholesterol with apoC-III; we’ll continue with our healthy habits, knowing that not only LDL is bad but that, in some circumstances, also HDL can be bad.
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