By David Liu PHD

Wednesday Sept 5, 2012 (foodconsumer.org) -- High plasma high density cholesterol (HDL) or commonly known as good cholesterol has been linked with reduced risk for myocardial infarction in some epidemiological studies.  A new study recently published in the Lancet suggests what is responsible for the reduced risk may not be HDL.

Benjamin F Voight of University of Pennsylvania and colleagues performed two Mendelian randomization analyses and found evidence suggesting that HDL is not the cause for the reduced risk of myocardial infarction.

First analysis was to test a single nucleotide polymorphism (SNP) in the endothelial lipase gene or LIPG Asn393Ser in 20,913 myocardial infarction cases and 95,407 controls in 20 studies.  The second analysis was to determine a genetic score consisting of 14 common SNPs that exclusively associate with HDL cholesterol.  A positive control used in the study has a genetic score of 13 common SNPs exclusively associated with LDL cholesterol.

Individuals with the LIPG 396Ser allele had higher HDL cholesterol (0.14 mmol/L higher), but similar concentrations of other lipids and non-lipid factors for myocardial infarction, compared to those without this allele.  This difference was expected to cause a decrease in risk of myocardial infarction by 13 percent.  But the 396Ser allele was not correlated with risk of myocardial infarction.

From observational or epidemiological studies, an increase of 1 SD in HDL cholesterol was correlated with 38 percent reduced risk of myocardial infarction. However, a 1 SD increase in HDL cholesterol due to genetic score was not correlated with the risk of myocardial infarction. 

On the other hand,  for low density cholesterol (LDL) or commonly known as bad cholesterol, a 1 SD increase in LDL cholesterol was associated with 54 percent increased risk for myocardial infarction. From genetic scoring, the risk was increased by 113 percent.  The two values were not the same, but on the same direction.

The researchers concluded "Some genetic mechanisms that raise plasma HDL cholesterol do not seem to lower risk of myocardial infarction. These data challenge the concept that raising of plasma HDL cholesterol will uniformly translate into reductions in risk of myocardial infarction."