The specific culprits include blood fats called triglycerides, as well as the size and number of certain cholesterol “particles” in the blood. Researchers say they may be better predictors of stroke risk than the traditional LDL number.
The study, reported in the journal Stroke, focused on 774 middle-aged and older U.S. women who suffered a stroke over about eight years. Each was compared with another stroke-free woman the same age and race.
Overall, the one-quarter of women with the highest triglycerides at the outset were 56 percent more likely to suffer a stroke than the one-quarter with the lowest triglycerides.
That doesn’t prove that the triglycerides are to blame. But the link held even when the researchers accounted for other stroke risk factors, like high blood pressure and diabetes.
And high triglycerides are already considered a risk factor for stroke, by groups like the American Heart Association (AHA).
“Studies such as ours really underscore the importance of triglycerides,” said lead researcher Dr. Jeffrey S. Berger, of New York University Medical Center.
According to the AHA, triglyceride levels of 150 to 199 milligrams per deciliter (mg/dL) are “borderline high,” while levels of 200 and up are considered “high.”
But while triglycerides were linked to strokes in this study, low-density lipoprotein—that is, “bad” LDL cholesterol—was not. Instead, more-specific measures of blood fats were.
That included so-called intermediate-density lipoprotein, or IDL. The one-quarter of women with the most IDL particles in their blood had a 46 percent higher stroke risk than the quarter of women with the lowest IDL numbers.
There was a similar effect when it came to the size of particles known as very low-density lipoprotein, or VLDL: Women with the largest VLDL particles had a higher stroke risk.
The study could only look at relative risks. So for any one woman with a lot of VLDL particles, for instance, it’s not clear how much of a stroke risk she would face.
“From this type of study, it’s not possible to understand the absolute risk,” Berger told Reuters Health.
But, he said, the findings do add to research from recent years suggesting that non-traditional measures of blood fat can be important.
Traditional numbers like total cholesterol and LDL, Berger said, “may really not be enough”—at least when it comes to the risk of ischemic stroke. (Ischemic strokes, which are caused by a clot that blocks blood flow to the brain, are the most common type of strokes.)
The new study was supported by the National Institute of Neurological Disorders and Stroke. One of the researchers is an employee of LipoScience, a company marketing a test that measures the number of cholesterol-carrying particles in the blood.
Berger said the findings don’t mean everyone needs to know their VLDLs and IDLs.
But some doctors, he noted, are already testing non-traditional markers—those other than LDL, “good” HDL cholesterol and triglycerides. That’s particularly true of preventive cardiologists, who see patients at higher-than-normal risk of heart attack and stroke.
According to Berger, non-traditional markers may be helpful for so-called “intermediate-risk” patients.
Those are people who are at higher-than-average risk of heart attack and stroke—because of factors like age and high blood pressure, for instance—but not considered “high-risk.” Someone with diabetes or a history of heart disease would automatically be considered high-risk.
Additional blood-fat measures might help weed out the intermediate-risk people who would benefit the most from therapies like a daily aspirin or cholesterol-lowering statins, according to Berger.
But so far, the tests haven’t been shown to help save lives or stave off strokes. The government-backed U.S. Preventive Services Task Force recommends screening women for blood fat problems if they are at increased risk of heart disease.
Berger said that when doctors order extra tests, it costs more money—another reason not to do them in everyone.
Experts say excessive medical testing may cost the U.S. up to $250 billion a year and is harming patients who end up getting invasive tests unnecessarily. The American College of Physicians, a leading medical group, is currently rolling out guidelines to curb the overuse.
Like the better known forms of cholesterol, VLDL and IDL can be changed through diet and exercise. And triglycerides, Berger said, are “very responsive” to lifestyle changes.
Cutting down on calories, starches, alcohol and saturated and trans fats often lowers triglyceride levels. Substituting “bad” fats with “good” ones—from olive oil and fish, for example—also helps, as does regular exercise.
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