Many people think that cholesterol levels, high blood pressure and high blood sugar are the end-all and be-all of gauging heart attack and stroke risk. But new evidence shows that a high level of white blood cells may be an entirely separate forecaster of cardiovascular events.
Measuring white blood cell levels to predict heart risk is not an entirely new idea. Previous studies have shown this simple blood test to be a useful measure for men, but a recent study, published in the Archives of Internal Medicine, was the first to look at white blood cell counts and heart disease risk for women, specifically postmenopausal women.
"This study represents a group that had been poorly represented in previous studies," said Dr. Karen Margolis, associate medical director of the Berman Center for Outcomes and Clinical Research at Hennepin County Medical Center in Minneapolis.
In the study, more than 72,000 women aged 50 to 79 were followed for an average length of six years. Their white blood cell counts were measured at the beginning of the study, and follow-up questionnaires or physicals were conducted annually. Ultimately, it was shown that women with a white blood cell count over 6.7 billion cells per liter, well above the average number of 5.8 billion cells per liter, were more than twice as likely to die from heart disease as women with lower white blood cell counts.
Previously, it has been shown that inflammation of the arteries contributes to atherosclerosis, the hardening and thickening of the arteries that leads to heart attack, stroke and death from heart disease. Although the connection between white blood cells and the inflammation of the arteries is not well understood, Margolis theorized that once a small lesion develops in an artery—from high blood pressure or high cholesterol levels, for example—white blood cells are attracted to that region. After they gather in the artery, white blood cells release disease-fighting chemicals, which may cause more inflammation and damage at the site. But it's also possible that white blood cells are just an indication of inflammation, not the root cause of it.
Be aware, though, a high white blood cell count isn't always cause for panic. High levels may also be caused by some medications, emotional stress or an infection. Be sure to discuss any concerns with a doctor.
"We're in a very early stage of figuring out how this works, but [our study] is one important step to understanding that inflammation is a key factor leading up to cardiovascular events," Margolis said. "It's possible that it's just the abundance of white blood cells that cause the inflammation, or they could just be a marker for disease; it's hard to know what came first, the chicken or the egg."
Interestingly, other studies have connected poor oral health, diabetes, high cholesterol and other risk factors for heart disease to high levels of white blood cells in the body.
It has also been shown that high blood levels of another marker inflammation, C-reactive protein (CRP), are tied to cardiovascular risk. However, white blood cell count tests are cheaper, more widely available and more automated than C-reactive protein tests, so one can compare results from different labs more easily. While white blood cell and CRP levels do not always correlate, the study showed that people with high levels of both white blood cells and CRP are at the highest risk; they were seven times more likely to suffer from cardiovascular disease than the average person.
Margolis suggests that women with a moderate risk of heart disease monitor their white blood cell count. If results show high levels of white blood cells, one should start taking steps to reduce other risk factors. Those at low risk have no need for this extra test and those at high-risk already know that they're at risk for cardiovascular disease, so this test doesn't provide any additional information. As always, exercise, healthy diet, eliminating smoking and coping with other risk factors are the best ways for these people to lower their risk.
"Inflammation is obviously a very important factor in the causation of cardiovascular events," Margolis said. "It has not been a factor in most risk equations until now and we need to understand how to use this information about white blood cells."