A study has raised questionsabout a widely held belief involving cholesterol.The belief is that high levels of so-calledgood cholesterol in the bloodcan reduce the risk of a heart attack.The medical name for "good" cholesterolis high-density lipoprotein, or HDL.Doctors commonly believe it reducesthe risk of heart attack by removing fatty depositsthat can block the flow of bloodin the arteries of the heart.But Dr. Sekar Kathiresanat Massachusetts General Hospital in Boston saysthe effects of high HDL have never been proven.He says the new study that he and other researchersdid suggests that HDL cholesteroldoes not affect the risk of heart attack.SEKAR KATHIRESAN: "This has been the major assumptionover the last thirty years, that if you raise HDL cholesterol,the risk for heart disease will be lowered.And I think we have now broken that assumption,broken that link using this gene variant."The researchers say about four percent of peoplehave a genetic changethat gives them a naturally high level of HDL.The study found that those who were genetically "programmed"to have higher HDL levels were just as likelyto suffer heart attacks as those who were not.A second analysis looked at fourteen gene variantsthat increase good cholesterol.Dr. Kathiresan says people with the most variantshad no more protection against heart attacks than anyone else.But he says there is no disputeabout low-density lipoprotein, or LDL. LDL,the so-called bad cholesterol,causes a buildup of fatty substances inside arteriesand increases the risk of heart attack.Dr. Kathiresan and his colleaguespublished their findings in the Lancet medical journal.Another widely held medical beliefhas also come into question recently.For years, men over the age of forty have been toldto get a simple blood test to see if they have prostate cancer.Now, experts on a government committee are advising them not to.Dr. Virginia Moyer heads the United StatesPreventive Services Task Force.VIRGINIA MOYER: "Close to two-thirds of older menhave prostate cancer and yet the huge majority of themnever have a problem from it in their lifetime."The task force examined two large studiesbefore deciding that treating the cancerfound by the PSA test can do more harm than good.Effects of the treatment can include a loss ofsexual ability and bladder control,as well as other problems including heart attacks.Some experts support the findings of the task force,but others disagree.Urologist Deepak Kapoor saysin about twenty years of PSA testing,death rates for prostate cancerhave dropped by thirty-eight percent.And that's the VOA Special English Health Report.