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Several years ago, I fell at the gym and ripped two tendons in my wrist. The pain was excruciating, and within minutes my hand had swollen grotesquely and become hot to the touch. I was reminded of a patient I’d seen early in medical school, whose bacterial infection extended from his knee to his toes. Latin was long absent from the teaching curriculum, but, as my instructor examined the leg, he cited the four classic symptoms of inflammation articulated by the Roman medical writer Celsus in the first century: rubor, redness; tumor, swelling; calor, heat; and dolor, pain. In Latin, inflammatiomeans “setting on fire,” and as I considered the searing pain in my injured hand I understood how the condition earned its name.
Inflammation occurs when the body rallies to defend itself against invading microbes or to heal damaged tissue. The walls of the capillaries dilate and grow more porous, enabling white blood cells to flood the damaged site. As blood flows in and fluid leaks out, the region swells, which can put pressure on surrounding nerves, causing pain; inflammatory molecules may also activate pain fibres. The heat most likely results from the increase in blood flow.
The key white blood cell in inflammation is called a macrophage, and for decades it has been a subject of study in my hematology laboratory and in many others. Macrophages were once cast as humble handmaidens of the immune system, responsible for recognizing microbes or debris and gobbling them up. But in recent years researchers have come to understand that macrophages are able to assemble, within themselves, specialized platforms that pump out the dozens of molecules that promote inflammation. These platforms, called inflammasomes, are like pop-up factories—quickly assembled when needed and quickly dismantled when the crisis has passed.
For centuries, scientists have debated whether inflammation is good or bad for us. Now we believe that it’s both: too little, and microbes fester and spread in the body, or wounds fail to heal; too much, and nearby healthy tissue can be degraded or destroyed. The fire of inflammation must be tightly controlled—turned on at the right moment and, just as critically, turned off. Lately, however, several lines of research have revealed that low-level inflammation can simmer quietly in the body, in the absence of overt trauma or infection, with profound implications for our health. Using advanced technologies, scientists have discovered that heart attacks, diabetes, and Alzheimer’s disease may be linked to smoldering inflammation, and some researchers have even speculated about its role in psychiatric conditions.
As a result, understanding and controlling inflammation has become a central goal of modern medical investigation. The internal research arm of the National Institutes of Health recently designated inflammation a priority, mobilizing several hundred scientists and hundreds of millions of dollars to better define its role in health and disease; in 2013, the journal Science devoted an entire issue to the subject. This explosion in activity has captured the public imagination. In best-selling books and on television and radio talk shows, threads of research are woven into cure-all tales in which inflammation is responsible for nearly every malady, and its defeat is the secret to health and longevity. New diets will counter the inflammation simmering in your gut and restore your mental equilibrium. Anti-inflammatory supplements will lift your depression and ameliorate autism. Certain drugs will tamp down the silent inflammation that degrades your tissues, improving your health and extending your life. Everything, and everyone, is inflamed.
ch claims aside, there is genuine evidence that inflammation plays a role in certain health conditions. In atherosclerosis, blood flow to the heart or the brain is blocked, resulting in a heart attack or a stroke. For a long time, atherosclerosis was thought to result mainly from eating fatty foods, which clogged the arteries. “Atherosclerosis was all about fats and grease,” Peter Libby, a professor at Harvard Medical School and a cardiologist at Brigham and Women’s Hospital, in Boston, told me recently. “Most physicians saw atherosclerosis as a straight plumbing problem.”
During his cardiology training, Libby studied immunology, and he became fascinated with the work of Rudolf Virchow, a nineteenth-century German pathologist. Virchow speculated that atherosclerosis might be an active process, caused by inflamed blood vessels, not one caused simply by the accumulation of fat. In the mid-nineteen-nineties, in studies with mice, Libby, working in parallel with other groups of scientists, found that low-density lipoproteins—LDLs, those particles of “bad” cholesterol—can work their way into the lining of arteries. There, they sometimes trigger an inflammatory response, which can cause blood clots that block the artery. Libby and others began to understand that atherosclerosis wasn’t a mere plumbing problem but also an immune disease—“our body’s defenses turned against ourselves,” he told me.
Paul Ridker, a cardiovascular expert and a colleague of Libby’s at Harvard and Brigham and Women’s, moved the research beyond the laboratory. He found that many patients who’d had heart attacks, despite lacking factors such as high blood pressure, high cholesterol, and a history of smoking, had an elevated level of C-reactive protein, a molecule produced in response to inflammation, in their blood. After demonstrating, in a separate study, that cholesterol-reducing statins could also reduce C-reactive-protein levels, Ridker launched the Jupiter trial, in which people with elevated levels of C-reactive protein but normal cholesterol levels were given a placebo or a statin medication. In 2008, the published results showed that the subjects who received the statin saw their levels of C-reactive protein drop and were less likely three and a half years later to suffer a heart attack. This suggested that elevated cholesterol isn’t the only factor at work in cardiovascular disease, and that in some cases statins, acting as anti-inflammatory agents, could be used to treat the condition.
The benefit was modest: the statin treatment reduced the risk of heart attack in only about one per cent of the patients. Still, that figure is statistically significant, and for one in every hundred patients—a hundred in every ten thousand—it’s meaningful. An independent safety-monitoring board ended the study early, saying that it was unethical to continue once it was clear that statins provided a benefit not available to the subjects on the placebo. (Critics argue that shortening the trial, which was funded by a drug company, exaggerated the potential benefits and underestimated long-term harm, but the researchers strongly disagree.) The N.I.H. and other scientific groups are funding new studies to further explore whether anti-inflammatory drugs—for example, low doses of immunomodulatory agents that are used for treating severe arthritis—can help prevent cardiovascular disease.
Another chronic condition that has been linked to inflammation is Type II diabetes. People with this condition can’t adequately use insulin, a molecule that enables the body’s cells to take glucose out of the bloodstream and derive energy from it. Their organs fail and glucose builds to dangerous levels in the blood. Recently, researchers have found macrophages in the pancreases of people with Type II diabetes. The macrophages release inflammatory molecules that are thought to impair insulin activity. One of these inflammatory molecules is called interleukin-1, and in 2007 the New England Journal of Medicine reported on a clinical trial in which an interleukin-1 blocker proved to be modestly effective at lowering blood-sugar levels in Type II diabetics. This suggests that, by blocking inflammation, it might be possible to restore insulin activity and alleviate some of the symptoms of diabetes.
Alzheimer’s disease, too, seems to show a link to inflammation. Alzheimer’s results from the buildup of amyloid and tau proteins in the brain; specialized cells called glial cells, which are related to macrophages, recognize these proteins as debris and release inflammatory molecules to get rid of them. This inflammation is thought to further impair the working of neurons, worsening Alzheimer’s. The connection is tantalizing, but it’s important to note that it doesn’t mean that inflammation causes Alzheimer’s. Nor is there strong evidence that inflammation contributes to other forms of dementia where the brain isn’t filled with protein debris. And in clinical trials anti-inflammatory drugs like naproxen and ibuprofen have failed to ameliorate or prevent Alzheimer’s.
On September 18, 2015, scientists at the N.I.H. convened a meeting to publicly present their research priorities, one of which is to decipher the consequences of inflammation. It’s increasingly apparent that inflammation plays some role in many health conditions, but scientists are far from grasping the nature of that relationship, the mechanisms involved, or the extent to which treating inflammation is helpful.
“We really don’t know how much inflammation contributes to diabetes, Alzheimer’s, depression, and other disorders,” Michael Gottesman, a director of research at the N.I.H., told me. “We know a lot about the mouse and its immune response. Much, much less is understood in humans. As we learn more, we see how much more we need to learn.” Gottesman pointed out that, of the thousand or so proteins circulating in our bloodstream, about a third are involved in inflammation and in our immune response, so simply detecting their presence doesn’t reveal much about their potential involvement in any particular disease. “Correlation is not causation,” he emphasized. “Because you find an inflammatory protein in a certain disorder, it doesn’t mean that it is causing that disorder.”
This lack of certainty hasn’t dampened the enthusiasm of a growing number of doctors who believe that inflammation is the source of a wide range of conditions, including dementia, depression, autism, A.D.H.D., and even aging. One of the most prominent such voices is that of Mark Hyman, whose books—including “The Blood Sugar Solution 10-Day Detox Diet”—are best-sellers. Hyman serves as a personal health adviser to Bill and Hillary Clinton and to the King and Queen of Jordan. Recently, he was recruited by the Cleveland Clinic with millions of dollars in funding to establish a center based on his ideas. Trained in family medicine, Hyman told me that he considers himself a new type of doctor. “I am a doctor who treats root causes and addresses the body as a dynamic system,” he wrote in an e-mail. “Being an inflammalogist is part of that.”
Studies with human subjects clearly indicate that, in cases where inflammation underlies a chronic condition, the inflammation is local: in the arteries (heart disease); or in the brain (Alzheimer’s); or in the pancreas (diabetes). And though there are associations between various forms of inflammatory disease—for example, people with psoriasis or periodontal disease have a somewhat higher risk of heart disease—it has not been proved that there is a causal connection. Hyman and other doctors, such as the neurologist David Perlmutter, promote a more radical idea: that certain foods and environmental toxins cause smoldering inflammation, which somehow spreads to other areas of the body, including the brain, degrading one’s health, mental acuity, and life span.
The notion of a gut-brain connection seems to derive from studies with mice, including one that showed that introducing a bacterium into a mouse’s gastrointestinal tract led to behavioral changes, such as a reluctance to navigate mazes. But there’s scant evidence that anything similar happens in people, or any rigorous study to show that “anti-inflammatory diets” reduce depression. Earlier this year, the journal Brain, Behavior, and Immunity published a meta-analysis of more than fifty clinical studies that found inflammatory molecules in patients with depression. The paper revealed that there was little consistency from study to study about which molecules correlated to the condition. Steven Hyman, a former director of the National Institute of Mental Health and now the head of the Stanley Center at the Broad Institute (and no relation to Mark Hyman), in Cambridge, Massachusetts, noted that depression is “one of those topics where exuberant theorization vastly outstrips the data.”
Nonetheless, Mark Hyman holds fast to his view. “Inflammation is the final common pathway for pretty much all chronic diseases,” he told me. His recommended solution is an “anti-inflammatory diet”—omitting sugar, caffeine, beans, dairy, gluten, and processed foods, as well as taking a variety of supplements, including probiotics, fish oil, Vitamins C and D, and curcumin, a key molecule in turmeric. Hyman introduced me to one of the patients he had treated with his anti-inflammatory diet and supplements, a forty-seven-year-old hedge-fund manager in Cambridge named Jim Silverman. Two decades ago, Silverman began noticing blood in his stool. A colonoscopy resulted in a diagnosis of ulcerative colitis. In the ensuing years, Silverman was treated by gastroenterologists with aspirin-based medication, anti-inflammatory suppositories, and even corticosteroids, but the problem persisted. Then, five years ago, on a flight home from a business conference, he happened to sit next to Hyman, who told him that he could cure colitis.
“I thought, What a bullshitter,” Silverman said. He travelled anyway to Hyman’s UltraWellness Center, in Lenox, Massachusetts, to consult with him. Hyman told him that dairy was inflaming his bowel. Silverman was skeptical, but he kept track of his diet and bleeding episodes, and ultimately concluded that restricting dairy products resulted in long periods without bleeding. He now thinks that he could be suffering from a dairy allergy. In addition to avoiding dairy products, he continues to follow the anti-inflammatory regimen of supplements prescribed by Hyman. “I’m just taking it because I’m doing well,” he said. “I have no idea if it’s doing anything, but I don’t want to rock the boat.”
I asked Gary Wu, a professor of gastroenterology at the Perelman School of Medicine, at the University of Pennsylvania, and one of the world’s experts on the gut microbiome, about the alleged value of treating inflammatory bowel disease by restricting specific foods. Recently, in the journal Gastroenterology, Wu and his colleagues published a comprehensive review of scientific studies on diet and inflammatory bowel disease. They found only two dietary interventions that had been proved to reduce inflammation: an “elemental diet,” which is a liquid mixture of amino acids, simple sugars, and triglycerides, and a slightly more complex liquid diet. The liquid mixtures are typically administered with a tube placed through the nose. “The diet is not palatable,” Wu said. “And you don’t eat during the day. There is no intake of whole foods at all.”
David Agus, a cancer specialist and a professor of medicine and engineering at the University of Southern California, is equally skeptical of Hyman’s claims for the anti-inflammation diet. Agus, who is perhaps best known for being the doctor on “CBS This Morning,” recently received a multimillion-dollar grant from the National Cancer Institute to study how inflammation may spur the growth of tumors. “This notion that foods cause inflammation and foods can block inflammation, there’s zero data that it changes clinical outcomes,” he told me. “If the idea gets people to eat fruits and vegetables, I love it, but it’s not real.” Agus noted that vitamins don’t counter inflammation, and that it’s been shown, in rigorous clinical trials, that they may increase one’s risk of developing cancer.
Still, Agus views inflammation as a component not only of cancer but also of chronic diseases like diabetes and dementia. Rather than special diets, he supports preventively taking approved anti-inflammatory medications, such as aspirin and statins, and scrupulously scheduling the standard vaccinations in order to prevent infections. In “The End of Illness,” Agus encourages the reader to “reduce your daily dose of inflammation” by, among other things, not wearing high heels, since these can inflame your feet and the inflammation could possibly affect your vital organs. When I pressed him on that suggestion, he told me, “What I meant is that if your feet hurt all day it’s probably not a good thing. The downside is you just wear a different pair of shoes. The upside is it gave you an understanding of inflammation and its role in disease.”
Mark Hyman, at times, acknowledges the possible limits of his paradigm. When I asked him about the alleged link among gut inflammation, diet, and psychological disorders, he conceded that some of his evidence was anecdotal, derived from his own clinical practice. He mentioned the case of a child with asthma, eczema, and A.D.H.D., whom he treated with “an elimination diet, taking him off processed foods, and giving him supplements.” The child’s allergic problems improved and his behavior was markedly better, Hyman said: “It was a light-bulb moment. I saw secondary effects on the brain that came out of treating physical problems.”
He also cited studies of patients with rheumatoid arthritis, a painful and debilitating auto-immune condition that inflames and erodes the joints, who became less depressed after being treated with inflammatory blockers. But had the anti-inflammatory treatment directly lifted their depression, or had their mood improved simply because they were more mobile and in less pain? I told Hyman that it was hard to connect the dots. “For sure,” he said.
Connecting the dots is a challenge even for scientists who are actively involved in inflammation research. One afternoon, I visited Ramnik Xavier, the chair of gastroenterology at Massachusetts General Hospital and an expert in Crohn’s disease and ulcerative colitis. The bowel is inflamed in both conditions: ulcerative colitis affects the colon, whereas Crohn’s disease can affect any part of the digestive system. But the nature of inflammation varies almost from person to person and involves interactions among DNA, many kinds of gastrointestinal cells, and the peculiarities of the gut microbiome. “Lots of cells, lots of genes, lots of bugs,” Xavier said.
Xavier, a compact man with a laconic manner and thick black hair marked by streaks of gray, initially studied the role of specialized white blood cells, known as T-cells and B-cells, in defending the body against the development of colitis. Eventually, with Mark Daly, a geneticist at the Broad Institute, Xavier began to search for genes that predispose people to inflammatory bowel disease and for genes that might protect them against it. The two scientists, as part of an international consortium, have identified at least a hundred and sixty areas of DNA that are associated with an increased risk of inflammatory bowel disease; Xavier’s lab has zeroed in on about two dozen genes within these regions of DNA.
One of the frustrations of treating inflammation is that our weapons against it are so imprecise. Drugs like naproxen and ibuprofen are the equivalent of peashooters. At the other extreme, cannon-like steroids shut down the immune system, raising the risk of infection, eroding the bones, predisposing the patient to diabetes, and causing mood swings. Even the peashooters can cause collateral damage: aspirin may help to protect against colon cancer, heart attack, and stroke, but it also raises the risk of gastrointestinal bleeding. Ibuprofen, naproxen, and similar drugs were labelled by the F.D.A. as increasing the risk of heart attack and stroke in people who’ve never suffered either condition, and clinical trials failed to show that they prevent or ameliorate dementia. (Although these drugs reduce inflammation, they may also alter the lining of blood vessels and increase the risk of clots.) Statins lower the chance of a heart attack, but there is growing concern not only about the side effect of muscle pain but also about increasing the likelihood of diabetes. And the absolute benefits of these preventive medications is slight, measured in single digits.
In the lab at the Broad Institute, Xavier and his team were trying to discover new treatments that can block inflammation in a targeted manner. The day I visited, they were assessing molecules associated with colitis, especially one called interleukin-10, or IL-10, which is known to decrease inflammation. In a cavernous room, I watched as a robotic arm moved among racks of plastic plates, each containing hundreds of small wells in which chemical compounds were being tested. Some people with Crohn’s disease have genetic mutations that disable the salubrious effects of IL-10. Xavier is trying to identify molecules that can compensate for this deficiency, in the hope that such molecules might eventually be turned into drugs to treat this subset of patients.
But other patients suffer from a different manifestation of Crohn’s—they can’t fully clear debris from cells in their gut, so it builds up, triggering inflammation. In a neighboring lab, members of Xavier’s research team were trying to develop drugs for that condition, too. A robotic arm was handling plates that contained genetically engineered cells and moving them under a fluorescent microscope. The images appeared on a computer screen—fields of cells studded with yellow and green dots, like the sky in van Gogh’s “Starry Night.”
On another visit, Xavier took me to his clinic at Mass General. Patients, ranging from the very young to the elderly, were reclining in Barcaloungers as nurses and physicians intravenously administered potent anti-inflammatory drugs. Later, I spoke by phone to one of Xavier’s patients, a forty-nine-year-old woman named Maria Ray, who received a diagnosis of colitis in 1998. She was treated with sulfa drugs and corticosteroids, which controlled the problem for several years, but in 2004, after a series of flare-ups, she underwent surgery to remove her colon. Soon after, she developed ulcers on her skin, arthritis of her knees and elbows, and inflammation in both eyes. Xavier prescribed other drugs, and for two years her condition improved, but lately her skin lesions and eye inflammation have returned. “We hoped surgery would cure her ulcerative colitis,” Xavier said. “But we don’t really understand why there is such an overactive immune system now inflaming these other parts of her body.”
At the very least, the fact that Ray has symptoms in many organs, despite the removal of her colon, complicates the simplistic view that treating the gut will suppress inflammation elsewhere. Moreover, there’s no evidence that patients with Crohn’s or colitis are more likely than average to develop dementia and other cognitive disorders. “What we see in mice is not always reproduced in people,” Xavier said.
Perhaps no aspect of inflammation is more compelling, or illusory, than the idea that it may be responsible for aging. An internist friend in Manhattan told me that healthy patients occasionally come in to her office carrying Mark Hyman’s books, eager to live longer by following his anti-inflammation life style. When I asked Hyman if he could introduce me to someone who follows his longevity regimen, he readily offered himself. “I’m aiming to live to a hundred and twenty,” he said.
The notion stems from grains of evidence, such as studies that have shown an increase in inflammation with age. The genesis of aging is still a mystery. It may occur for a host of reasons—a waning of the energy generated by the mitochondria within cells, the tendency of DNA to grow fragile and more mutation-prone over time—and it’s much too simplistic to attribute the process to inflammation alone. Luigi Ferrucci, the scientific director of the National Institute on Aging, conducted some of the early research on inflammation and aging, and for a while, he told me, he believed the avenue held promise. On the morning we spoke, he had just finished his daily six-mile run. Sixty-one years old, born in Livorno, on the coast of Tuscany, Ferrucci is an animated man with a stubbly beard who favors crew-neck sweaters. In the past four decades, he has studied thousands of people in order to identify the biological processes that result in aging. He measured scores of molecules in the blood, hoping to find clues that would lead him to the cause of aging’s hallmarks, particularly sarcopenia, or loss of muscle mass, and cognitive decline.
His most illuminating studies involved people in late middle age who showed no sign of heart disease, diabetes, dementia, or other conditions that might be associated with inflammation. He found that a single inflammatory molecule, called interleukin-6, was the most powerful predictor of who would eventually become disabled. Healthy patients with high levels of the IL-6 molecule aged more quickly and grew sicker than those without the inflammatory molecule. “I thought I had discovered the cause of aging and was going to win the Nobel Prize,” Ferrucci said, laughing.
But then he found other subjects with no evidence of inflammation, and without elevated levels of IL-6 or other inflammatory molecules, whose bodies nevertheless began to decline. “We are looking at the layer, not at the core of the problem,” he said. “Inflammation may accelerate aging in some people—but it is a manifestation of something that is occurring underneath.” He reiterated the point that correlation is not causation. “If you have the curiosity of the scientist, you can’t stop there, because you want to know why,” he said. “You want to break the toy so you can see how it’s working inside.”
Toward that end, Ferrucci recently organized a large team of collaborators and launched a new clinical study, gestalt, which stands for Genetic and Epigenetic Signatures of Translational Aging Laboratory Testing. Groups of healthy people will be studied intensively as they age, with detailed analyses of their DNA, RNA, proteins, metabolic capacity, and other sophisticated parameters, every two years for at least a decade. “Then we can say what mechanisms account for increased inflammation with aging, and the loss of muscle mass, or the loss of memory, or the loss of energy capacity or fitness,” Ferrucci said. “These have never really been addressed on a deep level in humans.”
In the meantime, he sticks to a Mediterranean diet, mainly out of fealty to his heritage. (Ferrucci is known among his N.I.H. colleagues as a gourmet Italian cook.) The media recently gave much attention to a study, published in 2013 in theNew England Journal of Medicine, on the benefits of a Mediterranean diet in preventing heart attack or stroke. But, as Ferrucci noted, the benefits weren’t clearly related to inflammation and they accrued to a very small percentage of the subjects on the diet. “Believe me, if there were a diet that prevented aging, I would be on it,” he said.
We’d all like a simple solution for complex medical problems. We’re desperate to feel in command of our lives, particularly as we age and see friends and family afflicted by Alzheimer’s, stroke, and heart failure. “My patients, understandably, are very focussed on the foods they eat, wanting control, hoping they won’t have to take immune-suppressive treatments,” Gary Wu, the University of Pennsylvania gastroenterologist, told me.
Some years ago, I became obsessed with a restrictive diet—no bread, cheese, ice cream, cookies—in an attempt to lower my cholesterol levels. (My father died of a heart attack in his fifties, and I was haunted by his fate.) After nearly six months, I’d lost some fifteen pounds, but my cholesterol level had hardly budged, and I’d become so vigilant about everything I ate that I stopped enjoying meals. Gradually, I resumed a balanced and more reasonable diet and regained an appreciation for one of life’s fundamental pleasures.
Scientists may yet discover that inflammation contributes to disease in unexpected ways. But it’s important to remember, too, that inflammation serves a vital role in the body. “We are playing with one of the primary mechanisms selected by nature to maintain the integrity of our body against the thousand environmental attacks that we receive every day,” Ferrucci said. “Inflammation is part of our maintenance and repair system. Without it, we can’t heal.”