Inflammation is a 'double-edged sword': How to protect against chronic disease

NBC News

04-03-2025

Why do our ankles swell when they're sprained or does our skin turn red — or inflamed — when it's scraped?
That quick response is caused by inflammation — and it can save your life.
At its core, inflammation is the 'response of the body to an illness or an injury to try to restore health,' said Dr. Robert Shmerling, a rheumatologist and faculty member at Harvard Medical School who helped author a report on inflammation.
Inflammation has come under fire for its link to a variety of chronic diseases, including diabetes, heart disease and even allergies. Longevity experts even see reducing chronic inflammation as key to healthier aging.
'It's a classic double-edged sword,' said Dr. David Hafler, a neurologist and professor of immunobiology at Yale School of Medicine.
Inflammation is necessary for survival, and without it our bodies wouldn't be able to fight off intruders like viruses and bacteria. A sore throat, for example, turns red and is painful because the immune system is fighting the infection to prevent it from spreading, which doctors call acute inflammation, said Dr. Moshe Arditi, a pediatrician and director of the infectious and immunological diseases research center at Cedars-Sinai Medical Center in Los Angeles.
'Localized immune response in the acute stage — to a limited extent — is all beneficial inflammation,' he said.
The discovery of inflammation dates back centuries to the Roman encyclopedist Aulus Cornelius Celcus, one of the first people to define it. Celcus described the core signs of inflammation in Latin as rubor, tumor, calore, delore. The terms translate to redness, swelling, heat and pain, which still hold true.
At a microscopic level, acute inflammation includes our bodies' sending fluid, proteins and white blood cells to the sites of infections or injuries, which help fight foreign pathogens and promote healing.
While inflammation can be lifesaving in the short term, there is another type of inflammation, chronic inflammation, that can damage the body over the long term.
What causes chronic inflammation?
Several risk factors make your body more likely to have chronic inflammation — including obesity, which promotes a low-level inflammatory state throughout the body, tobacco smoking and diet.
Dr. Thaddeus Stappenbeck, chair of inflammation and immunity at the Cleveland Clinic, suspects the modern American diet is a major source of chronic inflammation.
Processed foods, refined sugars, trans fats and excessive consumption of red meat are associated with increased inflammation. The Food and Drug Administration banned t rans fats in 2015, and they were finally removed from snacks, bread, cookies and other baked goods in 2018.
'I suspect that there's more people with underlying, chronic inflammation than there were in the past,' Stappenbeck said. 'I think about the way we've shifted our diet where we eat a lot of chemicals that we are not adapted to consume, and these have a number of effects on our intestines.'
Shmerling said, 'Lack of exercise, lack of sleep, too much stress, all of those are lifestyle factors associated that are pro-inflammatory.'
What are symptoms of inflammation?
Signs may vary, but they include:
Joint pain that doesn't improve.
Fatigue.
Constipation
Depression.
Weight loss, regular exercise and avoiding highly processed foods can reduce levels of inflammation in the body, Shmerling said. Studies have suggested that following a Mediterranean diet, largely plant-based with an emphasis on whole fruits and vegetables, can reduce levels of inflammation.
'It's often not an on/off kind of switch,' he said. 'We don't have perfect ways to measure inflammation after making a lifestyle modification, but inflammatory markers can improve with lifestyle changes.'
How chronic inflammation affects the heart
An estimated 129 million people in the United States have at least one chronic disease, according to the Centers for Disease Control and Prevention. The prevalence of chronic disease has grown by about 7 million people every five years, according to estimates from Stanford University.
The causes of chronic disease are complicated, but experts are increasingly convinced that inflammation is playing a role.
'There's a fair amount of consensus that a lot of the chronic diseases we see now in higher prevalence than in the past could well be related to chronic inflammation,' Shmerling said.
What comes first — the inflammation or the disease? When the body is in an inflammatory state, it can start to destroy the very things it needs to function, such as our vital organs and blood vessels.
'Ongoing inflammation may lead to heart disease and building of plaque in the blood vessels, which can lead to heart attack and strokes," said Arditi, of Cedars-Sinai. 'Long-term inflammation in your brain may lead to development of neurodegenerative diseases by damaging neurons and interfering with normal brain function.'
Autoimmune disorders like lupus or multiple sclerosis are also linked to chronic inflammation as the immune system starts to attack various parts of the body in friendly fire.
'The body is not distinguishing properly between itself and an outside intruder or a pathogen,' Shmerling said. 'There's chronic inflammation that's ongoing and quite damaging.'
Diseases including Parkinson's and even diabetes all have inflammatory components to them, Stappenbeck said. Because of inflammation's close relationship to a host of diseases, he's not surprised by patients coming in asking to be checked for it.
'I think there's a desire from patients to say, 'Can you actually detect this in me earlier, before I get super sick?'' he said.
Is there a test for chronic inflammation?
There are blood tests for inflammation, but they aren't perfect. They don't provide clear answers about where the inflammation may be lurking in the body.
There can also be false positives. That's why experts say the tests must be interpreted along with symptoms.
One of the most common tests is called the erythrocyte sedimentation rate, a blood test that measures the level of certain proteins that correlate with the amount of inflammation in the body.
Another test assesses c-reactive protein (CRP), a protein the liver produces in response to inflammation.
Because of the limitations, Shmerling doesn't recommend that healthy people with no symptoms be routinely screened for inflammation.
'There can be normal inflammation tests even when inflammation is present, and sometimes the tests are abnormal even when it doesn't seem there is any inflammation present,' he said. 'So they're not perfect.'
Stappenbeck agreed.
'I don't think there's much of a role for it, actually,' he said.
There is some potential for a test called hs-CRP, a more sensitive test that can find smaller increases in c-reactive protein in the blood. High levels of that protein in the blood have been linked to heart attacks and strokes.
Some argue that this test should be done routinely, just like checking cholesterol, to determine who is more at risk of heart attacks and stroke.
The evidence, however, has been mixed, which is why the test isn't widely performed.
'There are people who are so low-risk or so high-risk that it's very unlikely the CRP is going to help you,' Shmerling said. 'There are subsets of people, maybe at moderate risk, where a CRP for cardiac risk could be helpful.'