Triglyceride: The Hidden Spoiler
Much of what you’ve heard about triglycerides has made this compound
sound like cholesterol’s tag-along kid brother—annoying but not much of a threat.
Don’t believe it. Mounting research shows that this blood fat with the complex
name casts a long, menacing shadow in its own right.
You’re probably at least aware of the word “triglycerides.” It’s one of the dozens of medical terms that have worked their way into the lexicon of cardiac health in recent years. Maybe you even heard it from your own practitioner, who was telling you that your levels are too high. It’s probably time to pay attention.
Triglycerides are a type of fat found in the bloodstream. This little-understood substance is emerging as one of the body’s sinister scoundrels as it teams up with the more infamous spoiler cholesterol to wreak havoc, scientists increasingly believe, on the heart. Triglycerides may not share cholesterol’s spotlight, but more healthcare practitioners are taking another look at the compound and how it may do more than its fair share to contribute to obesity and many of the consequences associated with a wide girth: diabetes, heart attack, stroke and kidney failure.
“It’s underestimated and by far the most misunderstood of the heart disease risk factors,” says Michael Miller, MD, director of the Center for Preventive Cardiology at the University of Maryland Medical Center in Baltimore and associate professor of medicine and epidemiology at its medical school. “Triglycerides themselves are not harmful, and that’s why they are misunderstood. It’s kind of behind the scenes, but it’s a big instigator of trouble—very sneaky.”
Triglycerides have largely escaped scrutiny and concern as a heart disease risk factor because they do not behave like cholesterol, the material that builds up in the arteries and is therefore a more obvious menace. But triglycerides—the word refers to the three water-insoluble chains of carbon and hydrogen atoms in each triglyceride molecule—have been a more elusive culprit because they fluctuate wildly. And they break down into fatty acids, giving what some say is the misguided idea that they pose less of a risk. Low cholesterol levels, even though triglycerides may be high, also lull people into a false sense of immunity.
“It’s always been hard to do research in this area because triglycerides are so labile,” says John Morrison, PhD, a researcher at Cincinnati Children’s Hospital Medical Center. “They go up and down, they’re very fluctuating and not very steady. HDL [high-density lipoprotein, a type of cholesterol] is a very steady thing, so it’s easy to measure. It’s kind of reliable, whereas, even if you fast for 12 hours, your triglycerides will go way up if you were out the night before and had a bottle of wine with dinner.”
Triglycerides may also have gotten short shrift in research labs because a relatively small segment of the population manufactures excessive levels of the compound based solely on their genetic makeup. Most people are prone to high levels only when they become obese and do not exercise, says Gabriel Fernandez, PhD, professor of medicine at the University of Texas Health Science Center at San Antonio. “Triglycerides are one of the most neglected areas and that’s what contributes to killing diseases like pancreatitis or diabetes.”
Triglyceride levels less than 150 mg/dL are considered normal, levels between 150 and 199 mg/dL are borderline high and those from 200 to 499 mg/dL are high, according to guidelines set by the National Cholesterol Education Program (NCEP), an arm of the National Heart, Lung and Blood Institute. Some 3 million Americans have hypertriglyceride levels of above 500 mg/dL, a towering number, while another 22 to 25 million have triglyceride levels between 200 to 500 mg/dL, Fernandez notes.
Miller, the Baltimore cardiologist, said he expected to release new research early this year showing that triglycerides “contribute to hardening of the arteries in more ways than we have basically conceptualized.” Though he would not discuss many details of the research because it had not yet been published, he says the work puts triglycerides “in perspective relative to cholesterol.”
Even as triglycerides break down into fatty acids, they appear to cause the blood to thicken or clot, Miller says. “As we understand heart disease, the process of a heart attack is the combination of blood clotting on top of cholesterol plaque,” he says. Plaque narrows arteries; a heart attack or stroke happens when a clot gets stuck in the restricted vessel.
“If you think of triglycerides as the avenue of blood clotting rather than as hardening of the arteries, you can see a potential role where triglycerides may fit in,” Miller adds. “If you just focus on triglycerides causing hardening of the arteries you may get sidelined into a false belief. Triglycerides make the LDL cholesterol much more artheriogenic [likely to block arteries]. They are by themselves not artheriogenic but they promote the increase of hardening of the arteries through LDL.”
Miller has long wanted the NCEP guidelines adjusted downward, saying a triglyceride level of 150 mg/dL may be unhealthy. For more than a decade, he has called for setting the normal benchmark at 100 mg/dL for a wider margin of safety. Some of Miller’s early research came in 1996, when the NCEP benchmark for normal triglycerides was 200 mg/dL. Back then, a study of 460 men and women found that patients with levels of 100 and higher were twice as likely as patients with levels below 100 to have a heart attack.
A 100 mg/dL standard, Miller says, would also help minimize the risk that may come from high triglyceride levels that register after a meal. He bases this statement on his follow-up study in 2003, in which 50 healthy men and women of appropriate weight were given milkshakes with the fat content of an extra-large double hamburger and large shake. Four hours later, triglyceride levels in those with a so-called fasting triglyceride between 101 and 149 rose to an average 200 mg/dL, while those with a fasting triglyceride of less than 100 peaked at 124 mg/dL, on average.
Average triglyceride levels among Americans, Miller says, are 134 mg/dL versus levels below 100 mg/dL seen in countries with low heart disease rates.
Health authorities, however, do not universally agree on lowering triglyceride standards. “Whenever you have guidelines, you try to be consistent with the current evidence and you try to make sure that the people at highest risk get treated and people at low risk are not overly treated,” says Neil J. Stone, MD, a member of the NCEP committee that helped draft the existing guidelines. He believes that setting a normal benchmark of 100 mg/dL might prompt people with levels slightly above that to begin taking medication, perhaps unnecessarily. He adds the committee would likely revisit the guidelines to evaluate new evidence as it arises.
Healthcare providers should be more aware of the dangers posed by high triglycerides no matter where the cutoff level eventually settles. Stone cites the following passage in the group’s 2002 report: “Greater emphasis should be placed on elevated triglycerides as a marker for increased risk for coronary heart disease.” The current guideline of 150 mg/dL “represents a target, especially in people who are overweight, obese, sedentary or cigarette smokers,” he says.
Traditional triglyceride testing is also being called into question. Because triglycerides rise after eating, their levels are generally measured after fasting from 9 to 12 hours, with only water allowed, to determine risk. But two studies, one of 26,500 women in the United States and one of about 7,600 women and 6,400 men in Denmark, support the measurement of triglycerides after meals have affected the body (JAMA 7/18/07).
Fasting may not link triglyceride levels with heart attacks or other cardiovascular problems, the Danish study showed, because “remnant” lipoprotein particles—a possible risk factor for hardening of the arteries—might not show up after fasting. Lipoproteins carry cholesterol, fat and protein through the blood.
Recent research also shows that the dangers posed by high triglycerides don’t stop with heart disease. For example, excessive cholesterol and triglyceride levels do not let the immune system’s cells function normally, says Fernandez of the University of Texas.
The connections among exercise, a proper diet and weight loss are well documented, and recent research now links walking with lower triglycerides. Researchers from Scotland’s University of Glasgow showed that men who walked moderately for 90 minutes on a treadmill before a fatty meal registered triglyceride levels 25% lower than men who had not exercised. If you don’t have 90 minutes, two or three smaller sessions could yield similar results.
In addition to eating right and staying active, research shows that a number of natural compounds can help stave off high triglycerides or their harmful effects.
A Mexican study published in Lipids in Health and Disease in November showed that 36 men and women who took the algae spirulina saw significant decreases in triaglycerols (a form of triglyceride) and total cholesterol. Blood pressure was also reduced.
In a study out of Taiwan, natural antioxidant flavonoids and phenolic acids were found to inhibit fat formation. The study, published in the Journal of Agricultural and Food Chemistry in September, cited o-coumaric acid, found in the spice and herbal remedy turmeric, and the bioflavonoid rutin as the strongest inhibitors of the glycerol-3 phosphate dehydrogenase (GPDH) enzyme that forms triglycerides.
Noni, a South Pacific plant used in Polynesian folk medicine, was found to reduce cholesterol and triglycerides in a 2006 study by Mian-Ying Wang of the University of Illinois. And omega-3 fats found in salmon, sardines, walnuts and flaxseed oil are also often recommended. Fish oils, as well as the B vitamin niacin, increase the density of lipoproteins, making them difficult to enter and thicken blood vessels, Fernandez says.
The threat posed by high triglycerides is finally coming out into the open. So know your level and take steps to keep this once-hidden danger at bay. Next time you go for bloodwork, get your cholesterol—and your triglycerides—checked.