Most of us think of inflammation as the redness and swelling that follow a wound, infection or injury, such as an ankle sprain, or from overdoing a sport, “tennis elbow,” for example. This is “acute” inflammation, a beneficial immune system response that encourages healing, and usually disappears once the injury improves.
But chronic inflammation is less obvious and often more insidious.
Chronic inflammation begins without an apparent cause — and doesn’t stop. The immune system becomes activated, but the inflammatory response isn’t intermittent, as it is during an acute injury or infection. Rather, it stays on all the time at a low level.
Experts think this may be the result of an infection that doesn’t resolve, an abnormal immune reaction or such lifestyle factors as obesity, poor sleep or exposure to environmental toxins. Over time, the condition can, among other things, damage DNA and lead to heart disease, cancer and other serious disorders.
“Unlike acute inflammation, which benefits health by promoting healing and recovery, chronic inflammation is characterized by persistent increases in inflammatory proteins all throughout the body and can damage health and promote several major diseases,” says George Slavich, associate professor of psychiatry and biobehavioral sciences at UCLA, referring to small proteins called cytokines that the immune system releases at the site of an injury to promote recovery.
“People typically don’t know that they have chronic inflammation until it’s too late,” he says.
Individuals often learn they have chronic inflammation when they develop an autoimmune disease, such as Crohn’s disease, lupus, or Type 1 diabetes, since inflammation is a hallmark of autoimmune disorders. But experts believe chronic inflammation also plays a role in developing heart disease, cancer, kidney disease, nonalcoholic fatty liver disease, neurodegenerative disorders, cognitive decline and mental health illnesses, such as depression, post-traumatic stress disorder and schizophrenia.
Scientists are still learning about why chronic inflammation is so dangerous and how it contributes to disease. Meanwhile, they suggest actions people can take to reduce their risk, specifically by changing certain behaviors.
Numerous factors appear to raise the risk of chronic inflammation, among them social isolation, psychological stress, disturbed sleep, chronic infections, physical inactivity, poor diet, obesity and exposure to air pollutants, hazardous waste products, industrial chemicals and tobacco smoke.
Experts believe individuals can reduce their risk by adopting lifestyle changes, including eating a healthy diet, improving sleep, exercising regularly, quitting smoking and finding ways to decrease stress and exposure to environmental pollutants.
“Diet is one of the key factors that influences inflammation in the body,” Slavich says. “Whereas fried foods, red meat, sodas, and white bread and pastries that have refined carbohydrates tend to increase inflammation, fruits, nuts, green leafy vegetables, tomatoes and olive oil tend to reduce inflammation. Therefore, while diet is not the only factor that can be targeted to improve immune health, it is an important one.”
Scientists think chronic inflammation causes oxidative stress in the body, which is an imbalance between the production of dangerous free radicals, molecules that harm healthy tissue in the body, and antioxidants, substances that clean up waste products and neutralize them. This can damage DNA as well as proteins and fatty tissue, which in turn accelerates biological aging.
“Chronic inflammation is involved in not just a few select disorders but a wide variety of very serious physical and mental health conditions,” says Slavich, senior author of a paper signed by scientists from 22 institutions urging greater prevention, early diagnosis and treatment of severe chronic inflammation. “Indeed, chronic inflammatory diseases are the most significant cause of death in the world today, with more than 50 percent of all deaths being attributable to inflammation-related diseases.”
Researchers still don’t understand the exact mechanisms of how certain behaviors influence chronic inflammation, although a few examples are clear. In heart disease, for example, cigarette smoking and air pollution irritate the arteries, which stimulates inflammation.
“The ‘damage accumulation’ theory is a possibility, but the reality is that we do not know whether inflammation is causing these health and functional problems, or whether it’s an indication that some other process is evolving that undermines health,” says Luigi Ferrucci, scientific director of the National Institute on Aging. “The evidence is clearer for cardiovascular disease, since it has been demonstrated that blocking inflammation with specific drugs prevents cardiovascular events. For the other outcomes, it’s still uncertain.”
Chronic inflammation can contribute to cognitive decline and mental health disorders by boosting age-related immune system deterioration, known as immunosenescence, and by promoting vascular and brain aging, which, in combination, degrade neural and cognitive function, experts say.
“Chronic inflammation can also cause threat sensitivity and hypervigilance, which gives rise to anxiety disorders and PTSD, as well as fatigue and social-behavioral withdrawal, which are key symptoms of depression,” Slavich says.
Scientists say more research is needed to identify biomarkers or other substances that suggest the presence of chronic inflammation.
There are probably hundreds of these potential diagnostic tools produced by the immune system, but they remain unidentified, Slavich says.
The most widely used test measures levels of C-reactive protein (CRP) in the blood. CRP, a substance produced by the liver, rises when chronic inflammation is present, although the standard CRP test is nonspecific — that is, it indicates inflammation, but cannot pinpoint exactly where it is. A second, more sensitive test (hs-CRP) suggests a higher risk of heart attack, although it too can be imprecise.
Some doctors screen for CRP as part of routine physical exams and also among people at risk for heart disease and autoimmune conditions. Experts think wider screening could identify more patients. “This isn’t a bad idea,” Ferrucci says.
Another test — this one more specific to heart disease — screens for myeloperoxidase, or MPO, an enzyme released by white blood cells that kills harmful bacteria in inflamed blood vessels. Increases in MPO can be dangerous, causing further damage to arterial walls, which encourages the formation of clots. These, in turn, can block blood flow, leading to heart attack and stroke. MPO also reduces the effectiveness of HDL, the “good” cholesterol, and removes nitric oxide, which is important for the regulation of healthy blood flow.
The good news, however, is that people worried about developing chronic inflammation can take affirmative steps to prevent it.
“If we make people aware of these risk factors, our hope is that individuals will reduce the factors that apply to them,” Slavich says.