TUESDAY, July 17, 2007 (HealthDay News) -- In findings that could change the way cholesterol tests are done, two studies show that high blood levels of the fats called triglycerides are associated with an increased risk of cardiovascular problems such as heart attack.
But that holds true only if the triglycerides are measured in the hours immediately after a meal.
The studies, one done in Denmark, the other in the United States, found such a relationship in what are called "nonfasting tests." One study found no relationship when blood fat levels were measured in the usual way -- after a 12- to 14-hour fast.
The nonfasting test results were striking, said Dr. Borge G. Nordestgaard, professor of medicine at Herlev University Hospital in Denmark and lead author of one of the two reports in the July 18 issue of the Journal of the American Medical Association.
"The main and most important finding is that people with very high triglyceride levels had a major increase in myocardial infarct [heart attack]," Nordestgaard said. "So far, this has mainly been ignored by clinicians. They have focused on cholesterol."
In the study, which followed almost 14,000 residents of Copenhagen for an average of 26 years, women with the highest blood levels of triglycerides when tested in the hours after a meal had up to five times the risk of dying from a heart attack or other cardiovascular event than those with the lowest levels. Men with the highest triglyceride levels had double the risk of those with the lowest levels. The difference between the genders was probably due to the fact that men in Denmark tend to be heavy drinkers, and alcohol affects blood triglyceride levels, Nordestgaard said.
The American study, done by Harvard researchers, included more than 25,000 participants in the Women's Health Study who were followed for an average of more than 11 years. The study found a 44 percent increased risk of an adverse cardiovascular event in women with the highest triglyceride levels in the hours immediately after a meal. The triglyceride-associated risk decreased steadily in the hours after a meal, vanishing after about four hours.
Past research has shown a relationship between high triglyceride levels and cardiovascular risk, said Dr. Patrick E. McBride, professor of medicine at the University of Wisconsin School of Medicine and Public Health and author of an accompanying editorial in the journal. "But these are the first studies I've seen that show that a nonfasting test is a better predictor of risk," he said.
The concept of triglycerides is often difficult to explain to nonscientists, McBride said. "They are the first fats that come into the bloodstream after we eat," he said, and then are processed by the body into the full range of blood fats, including LDL cholesterol, the "bad" kind that clogs arteries, and HDL cholesterol, the "good" kind that prevents formation of artery-blocking deposits.
"In the past decade, we have learned that after a meal, triglyceride levels stay up in some people for a short time but can stay up in some people for many hours," McBride said. Referring to the standard practice of requiring a long fast before a blood fat test, "we may have missed the boat and should have looked to see what it was like when someone was living a normal life," he said.
The new study results "suggest we look more carefully at when a blood test should be done," McBride said. "But I don't say we are ready to abandon the current practice."
Whatever the testing routine may ultimately turn out to be, dangerously high triglyceride levels require the same corrective measures as high cholesterol levels, McBride said, with close attention to the well-known risk factors such as high blood pressure, obesity, diabetes and inactivity.
You can learn more about triglycerides at the American Heart Association.