Having naturally high levels of "good" cholesterol doesn't lower the risk of heart attacks as believed.
LDL cholesterol is referred to as "bad" cholesterol because when there's too much, it promotes the build-up of plaque in artery walls.
HDL cholesterol is known as "good" cholesterol because higher concentrations have been associated with lower risk of heart attacks in observational studies.
The hoped for benefits of increasing high-density lipoprotein or HDL cholesterol for lowering heart attack risk haven't panned out in randomized trials of experimental drugs.
According to conventional wisdom, those who inherit genetic variants for higher HDL levels should have lower cardiovascular risk. When researchers tested 116,000 people, they found 2.6 per cent of them were genetically predisposed to have higher concentrations of HDL.
These people did have higher levels of HDL, but there was no evidence that they actually enjoyed a lower susceptibility to heart attack, also called myocardial infarction.
"Some genetic mechanisms that raise plasma HDL cholesterol do not seem to lower risk of myocardial infarction," Dr. Sekar Kathiresan of Harvard Medical School in Boston and his co-authors concluded in Thursday's issue of the medical journal The Lancet.
"If an intervention such as a drug raises HDL cholesterol, we cannot automatically assume that risk of myocardial infarction will be reduced."
The findings refute the thinking that low HDL plays a causal role in heart disease, Steve Humphries and his colleagues of University College London in the UK said in a journal commentary.
The observation from the genetic analysis "calls into question whether raising of HDL cholesterol therapeutically would translate into the expected clinical benefit," the commentators said.
Eating foods such as walnuts, almonds and salmon seems to help cholesterol levels.
The vitamin niacin was also proposed as a way of raising HDL but a U.S.-government funded trial into it was stopped early last year when those taking it showed no reduction in heart attacks and strokes.
The British Heart Foundation said the relationship between HDL and heart attack risk is complex and more research is needed to understand how it interacts with other risk factors.
"What we do know is that having too much harmful cholesterol in your blood can increase your risk of getting cardiovascular disease," said Shannon Amoils, the group's research advisor.
"A healthy lifestyle is vital to improve your overall cholesterol levels and protect your heart. Cutting down on fatty and sugary foods, as well as reducing the amount of alcohol you drink, will all have a beneficial effect on your heart health."
Many of the authors have received grants or are employed by pharmaceutical companies selling medications to lower LDL cholesterol levels.
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