Cholesterol is bad, right? Not exactly
When his patients want to talk about cholesterol, cardiologist Dariush Mozaffarian knows he has his work cut out for him. Confusion about the much-maligned substance is common: surveys of adults around the world show that although most people are concerned about their cholesterol, fewer than half know recommended cholesterol levels or understand what those numbers mean for their health.
"There's a lot of confusion and controversy around cholesterol," says Mozaffarian, an associate professor of medicine and epidemiology at Harvard Medical School. "There is even confusion among the scientists who study it."
That confusion can lead both patients and doctors astray, which is why Mozaffarian and many other physicians are working to dispel cholesterol myths.
"People talk and write about cholesterol as 'artery-clogging fat,' " Mozaffarian says. "But this idea that you eat something, it gets into your bloodstream and it clogs your arteries is just false. Nothing remotely like that is happening."
In fact, most of the cholesterol in your body doesn't come from food - it's made by the body itself. The liver produces this waxy, fatlike substance, which is just one component - along with calcium and other debris - of the plaque that can clog arteries and cause heart attacks and certain kinds of stroke. But most of the time, cholesterol isn't there to cause trouble; it travels through the bloodstream doing a number of important jobs. It helps make key hormones such as oestrogen and testosterone, synthesise vitamin D, and build and maintain cell membranes, all of which are "absolutely mandatory" for good health, says Michael Blaha, director of clinical research at the Johns Hopkins Ciccarone Centre for the Prevention of Heart Disease.
To transport and store cholesterol, the liver packages it into lipoproteins - particles that are part fat and part protein. Low-density lipoproteins (LDL) carry cholesterol to the body's cells; high-density lipoproteins (HDL) bring it back to the liver, where it gets recycled or excreted. Cholesterol tests, or "lipid panels," measure the levels of lipoproteins circulating in the blood, along with triglycerides, fats that are often packaged with lipoproteins.
In a healthy cardiovascular system, LDL, HDL and triglycerides are in balance. Smoking, lack of exercise, obesity, poor diet and other factors can throw the balance out of whack, and that's what sets the stage for plaque buildup and heart disease, Mozaffarian says.
THE GOOD AND THE BAD
Until recently, physicians focused on the total cholesterol level - the combination of LDL and HDL in the blood - when screening patients for heart disease risk, and they had good reason, says Paul Ridker, director of the Centre for Cardiovascular Disease Prevention at Brigham and Women's Hospital in Boston.
"Studies showed us that high cholesterol levels were one of the most important risk factors for the development of heart attack and stroke, and we had evidence that lowering cholesterol lowers the risk of heart attack and stroke," Ridker says. "You can't say that about most everything else."
But looking at just one number doesn't provide a detailed-enough picture to precisely assess risk, because it doesn't account for the interplay among LDL, HDL and triglycerides, or the fact that each of these affects risk in a different way, Mozaffarian says.
Several studies, including the Atherosclerosis Risk in Communities Study, which tracked more than 11,000 men and women over 11 years, have shown that high LDL (commonly referred to as "bad" cholesterol) levels are associated with greater risks of heart attack and stroke. High triglycerides can also spell trouble: a 2007 analysis found a significant association between high triglyceride levels and both fatal and non-fatal heart attacks and stroke. Yet studies dating to the late 1970s have shown that high levels of HDL, or "good" cholesterol, seem to protect against heart attacks and stroke. These findings have prompted many physicians to test for and evaluate LDL, HDL and triglycerides individually.
What does this mean for patients? Although the research is complex, the gist of it is simple, Blaha says: "HDL is good - the more you have, the lower your risk of heart disease. Everything else, you want to keep the levels low."
Specifically, the National Heart, Lung, and Blood Institute recommends a total cholesterol level of less than 200 milligrams per decilitre of blood, an LDL level of less than 100 mg/dL and an HDL level over 60 mg/dL for optimal health. Optimal triglyceride levels should come in below 100 mg/dL, according to a 2011 American Heart Association scientific statement.
HOW TO GET THE RIGHT BALANCE
Researchers agree about some of the ways to reach these cholesterol goals: losing weight, quitting smoking and exercising more have all been linked to more optimal cholesterol levels and lower heart disease risk. But there is some disagreement over which dietary changes are best for heart health, says Roger Blumenthal, director of the Ciccarone Centre.
Although physicians and U.S. dietary guidelines have long recommended that people with high total cholesterol or LDL avoid foods that are high in cholesterol, such as eggs, that advice may be overstated. "For most people, cholesterol from food isn't a contributor to their cholesterol levels," Blumenthal says.
High-fat foods, such as cheese and chocolate, have also been regarded as verboten, yet "the evidence for this may not be as strong as we once thought," he says.
In fact, a 2006 study of nearly 50,000 women showed that a low-fat diet did not protect them from heart disease or stroke. And a 2014 study co-authored by Mozaffarian that analysed data from 76 studies involving more than 600,000 participants found scant evidence to support recommendations that people avoid saturated fat - the kind found in such foods as red meat, butter and cheese, the kind that has long been vilified as bad for heart health.
"Basically, foods are more than just the cholesterol or just the fat in them," Mozaffarian says. "We need to eat healthy, minimally processed foods overall - especially plants and olive oil and nuts - and not define those foods by the nutrients they have or lack," he says, citing the 2013 PREDIMED study. That study tracked the health effects of a relatively high-fat Mediterranean-style diet - one that emphasised olive oil and nuts along with fruits, vegetables, fish and other unprocessed foods - vs. a low-fat diet in more than 7,000 participants. It found that the Mediterranean-style diet reduced the risk of heart attacks and stroke by about 30 percent.
WHEN LIFESTYLE CHANGES DON'T WORK
When food and lifestyle changes fail to bring a patient's cholesterol levels into line, many physicians turn to cholesterol-lowering medications called statins. Although statins are commonly prescribed and although clinical studies - including the JUPITER trial, a collaboration led by Ridker involving 1,315 physicians in 26 countries - have shown that they do reduce the number of heart attacks, even in people with normal LDL levels, the drugs remain controversial due to reports of serious side effects and a perceived push to prescribe them more frequently than is warranted.
New cholesterol treatment guidelines formulated by the American Heart Association and the American College of Cardiology rely on a formula, or "calculator," for heart disease risk that some researchers say could lead to overtreatment with statins. The new guidelines lower the threshold for treatment so that anyone with a 7.5 percent risk of a heart attack or stroke over the next 10 years is considered a candidate for statins.
According to researchers who worked on the guidelines and who support the lower threshold, the new guidelines mean that as many as 31 percent of Americans age 40 to 75 with no existing cardiovascular disease would be eligible for statin therapy.
For Ridker, who considers himself "pro-statin," that's just too many people. His own analysis suggests the new calculator overestimates risk by as much as 75 to 150 percent.
"If you're a man over age 66 or a woman over age 70, it says you automatically have a risk above the threshold for statin-taking," Ridker says. He says the new guidelines have value, especially in that they recommend counselling patients on lifestyle changes to control cholesterol as a first step, but they should be considered with care.
"We have to be physicians," he says. "We can't be robotic in how we apply these things."
Johns Hopkins' Blaha agrees. "These guidelines are a good starting tool," he says, "but we can't account for all the variability and complexity in your life with an equation."
That's why he, Ridker and Mozaffarian urge patients to discuss the issue with their health-care providers, to learn as much as they can about their options for preventing heart attack and stroke - and not to get too hung up on cholesterol.
"The biggest takeaway is that heart disease risk is about much more than cholesterol," Mozaffarian says. "Do you smoke? Are you active every day? Do you eat well? All of it matters. The key is your overall holistic health, and not just a single number on a piece of paper."
- Telis is a freelance health and science writer.
- The Washington Post