What is inflammation?

Ask the doctor


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Q. I often hear that inflammation is dangerous, especially in terms of contributing to heart disease. But what exactly is inflammation, and how do I know if I have it?

A. Think of inflammation as the body's natural response to protect itself against harm. There are two types: acute and chronic. You're probably more familiar with the acute type, which occurs when you bang your knee or cut your finger. Your immune system dispatches an army of white blood cells to surround and protect the area, creating visible redness and swelling. The process works similarly if you have an infection like the flu or pneumonia. So in these settings, inflammation is essential—without it, injuries could fester and simple infections could be deadly.

But chronic inflammation can also occur in response to other unwanted substances in the body, such as toxins from cigarette smoke or an excess of fat cells (especially fat in the belly area). Inside arteries, inflammation helps kick off atherosclerosis—the buildup of fatty, cholesterol-rich plaque. Your body perceives this plaque as abnormal and foreign, so it attempts to wall off the plaque from the flowing blood. But if that wall breaks down, the plaque may rupture. The contents then mingle with blood, forming a clot that blocks blood flow. These clots are responsible for the majority of heart attacks and most strokes.

A simple blood test called the hsCRP test can measure C-reactive protein (CRP), which is a marker for inflammation, including arterial inflammation. Nearly 20 years ago, Harvard researchers found that men with higher CRP levels—approximately 2 milligrams per liter (mg/L) or greater—had three times the risk of heart attack and twice the risk of stroke as men with little or no chronic inflammation. They also found that people with the greatest degree of arterial inflammation benefited the most from aspirin, a drug that helps prevent blood clots and also damps down inflammation.

But many doctors don't routinely recommend the hsCRP test because for the most part, they believe the results would not change your treatment. If you're young and healthy and at low risk for heart disease, there is no evidence that knowing your CRP level is helpful. If you have heart disease, you should already be taking medications that lower your heart attack risk, such as a cholesterol-lowering statin. Like aspirin, statins also appear to work particularly well in people with arterial inflammation. One study even showed that statins reduce the risk of death in people with average cholesterol levels but CRP levels of 2 mg/L or higher. So if you're middle-aged or beyond and have signs of looming heart trouble, like high blood pressure, high cholesterol, or a family history of heart disease, knowing that you have a high CRP level might nudge you toward more aggressive actions to protect your heart. These include doing regular aerobic exercise and (if needed) losing weight and quitting smoking.

— Deepak Bhatt, M.D., M.PH.
Editor in Chief, Harvard Heart Letter