CRP is an indicator of inflammation. High levels of CRP have been linked to increased risk of heart attack, stroke, and type 2 (non-insulin dependent) diabetes.
Metabolic syndrome is the clustering of three or more of five conditions: abdominal obesity, high triglycerides, low levels of "good" HDL cholesterol, high blood pressure, and high glucose (blood sugar). It is associated with a significant increase in cardiovascular risk.
In the study, Harvard researchers examined data from 14,719 healthy participants enrolled in the ongoing Women's Health Study (WHS), which began in late 1992. They excluded women receiving estrogen replacement therapy or who had diabetes.
Among the women, 3,597 had metabolic syndrome when they entered the WHS study.
After eight years of follow-up, the age-adjusted rate for heart attacks, strokes, operations to restore blood flow to the heart, and death from cardiovascular disease for those with metabolic syndrome and CRP levels above 3.0 milligrams per Liter (mg/L) was 5.9 per 1,000 people per year. For those with the metabolic syndrome but CRP levels less than 3.0 mg/L, the event rate was 3.4.
An analysis of the women with metabolic syndrome showed that those with the highest CRP levels (greater than 3.0 mg/L) were 2.1 times more likely to have a cardiovascular event than those with the lowest CRP levels (less than 1.0 mg/L).
"We have previously shown that CRP predicts cardiovascular risk in healthy individuals. Now we have evidence that CRP also does a very good job of distinguishing lower, moderate, and higher risk, even among people with metabolic syndrome," says lead author Paul M. Ridker, M.D., a professor of medicine at Harvard and director of the Center for Cardiovascular Disease Prevention at Brigham and Women's Hospital in Boston.
Although his team studied only women, "we believe these data are likely true for men because other studies have linked CRP to individual components of the metabolic syndrome," he says.
These results also add evidence to the hypotheses that inflammation plays a significant role in cardiovascular disease.
He also notes that "we don't yet have evidence that lowering CRP will necessarily lower cardiovascular risk. Studies evaluating this idea are only now starting."
Lifestyle changes such as a heart-healthy diet, regular exercise, weight loss and stopping smoking can reduce the risk of heart disease and diabetes.
Ridker's results support the new American Heart Association/Centers for Disease Control recommendations on the clinical use of CRP testing, which are published in the same issue of Circulation, says Thomas A. Pearson, M.D., Ph.D., co-chair of the writing group that crafted the new recommendations. "These recommendations suggest that CRP testing should be limited to those patients with intermediate risk, such as women with metabolic syndrome, and that hs-CRP testing is an optional tool to further define their coronary risk.
"Dr. Ridker's results confirm the importance of the metabolic syndrome as a predictor of coronary events in women," Pearson adds.
Co-authors are Julie E. Buring, M.D.; Nancy R. Cook, M.D.; and Nader Rifai, M.D. This study was supported partly by the National Heart, Lung and Blood Institute.
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