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Conflicting Opinions On HDL As ‘Good’ Cholesterol

May 18, 2012
Image Credit: argus / Shutterstock

Connie K. Ho for RedOrbit.com

High-density lipoprotein, otherwise known as HDL, was thought to be “good” cholesterol. However, a new study, based on databases of genetic information, disproves the HDL theory and states that rising HDL may not have any change to heart disease risk. As such, people who have inherited genes that have a high amount of HDL do not have any less of a chance of having heart disease than those who have inherited genes that have lower levels of HDL.

According to the New York Times, lipoproteins are composed of fat and protein. They are able to transport cholesterol, lipids, and triglycerides to other parts of the body via the blood stream. The research, published in a recent edition of the Lancet, discusses the effect of HDL levels in relation to heart diseases. The authors weren´t questioning whether HDL could or could not lower risk of heart disease; they were looking more at the causality of HDL. Based on their research, the scientists theorized that HDL moved cholesterol out of arteries that they weren´t supposed to be in.

“This is an interesting study because we´ve long held that HDL cholesterol and protective from epidemiological studies — and this is looking at if this has been the right course of thought,” Dr. Nieca Goldberg, a cardiologist and medical director of the Joan Tisch Center for Women’s Health at New York University´s Langone Medical Center, mentioned to Fox News.

In the project, Dr. Sekar Kathiresan, director of preventive cardiology at Massachusetts General Hospital and a geneticist at the Broad Institute of M.I.T. and Harvard, worked with colleagues in using Mendelian randomization, a method that has become more prominent due to quick and low-cost genetic analyses. One study looked at the variant in those who had experienced heart attacks, which was found in 21,000 people, as well as those with no heart attack history, which was found in 95,000 people. They looked at how people could inherit a wide variety of genetic variations and how the randomness determines how much HDL the genes will produce in a person. If HDL reduces the chance of heart disease, then those who have genes that produce more HDL will have less of a risk of having heart disease.

The researchers compared the studies of HDL to LDL, which is considered bad cholesterol. The researchers looked at 13 genes that had determined levels of LDL. They found that genes that raised LDL levels increased risk, while genes that lowered LDL levels decreased risk.

“That speaks to how powerful LDL is,” Kathiresan said in the New York Times article.

However, when the researchers examined endothelial lipase, a gene that affects only HDL, they found that the variation affected participants´ level by six points. About 2.6 percent of the population has that variation. Scientists observed data from 116,000 people on whether those who had the HDL-raising variant had a lower risk for heart disease.

“We found absolutely no association between the HDL-boosting variant and risk for heart disease,” noted Kathiresan in the New York Times article. “That was very surprising to us.”

According to WebMD, in the second study, the researchers continued by looking at a group of 14 gene variants that affected HDL levels. They wanted to find if there was a connection between the variants and a risk of heart disease. The data was based off 53,500 people. No link was found between increased HDL and the risk of heart disease. Kathiresan believes that HDL may be related to a number of things.

“The number of factors that track with low HDL is a mile long,” Kathiresan told the New York Times. “Obesity, being sedentary, smoking, insulin resistance, having small LDL particles, having increased cholesterol in remnant particles, and having increased amounts of coagulation factors in the blood“¦ Our hypothesis is that much of the association may be due to these other factors.”

Before the study was published, a number of companies had been developing drugs that could raise HDL levels. According to Forbes, previous HDL-boosting drugs haven´t always been able to prevent heart attacks. This includes Pfizer´s experimental drug torcetrapib that boosted HDL, but also increased the death rate in the clinical trial. A Roche drug, similar to the Pfizer medication, was stopped as well because there wasn´t much of a chance that it would show tangible benefits after boosting HDL levels. Besides the drugs, patients who had low HDL levels were advised to raise these levels through exercising, dieting, or taking the vitamin niacin.

As a result of the report, some doctors are skeptical of the role HDL plays in the risk of heart disease.

“The current study tells us that when it comes to HDL we should seriously consider going back to the drawing board, in this case meaning back to the laboratory,” Dr. Michael Lauer, director of the division of cardiovascular sciences at the National Heart, Lung and Blood Institute, told the New York Times. Lauer is unaffiliated with the study. “We need to encourage basic laboratory scientists to figure out where HDL fits in the puzzle – just what exactly is it a marker for.”

However, other physicians and researcher remain optimistic about HDL.

“It´s certainly a strike against the overall HDL hypothesis. But I for one am not convinced that we should abandon HDL,” Daniel Rader, a researcher at the University of Pennsylvania and a coauthor on the Lancet paper, told Forbes.


Source: Connie K. Ho for RedOrbit.com



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