Research shows that stress, the body’s response to feeling challenged or threatened, induces or worsens medical conditions, including depression, cardiovascular diseases, neurodegenerative diseases, and cancer.

But the exact mechanism by which stress induces disease has remained a mystery. Until now.

A study review concluded that inflammation is a common pathway of stress-related diseases.

“Chronic inflammation is an essential component of chronic diseases,” the authors wrote.

Still, the pathway from stress to inflammation to disease isn’t always clear.

“There’s no one simple answer,” says Alka Gupta, MD, codirector of integrative health at the Brain and Spine Institute at Weill Cornell Medicine in New York City. “We do know, though, that when we teach people how to reduce stress in whatever form — stress management tips, classes, individual advice, yoga, deep breathing — we see decreases in some of these inflammatory side effects.”

So if we can understand the ways in which chronic stress leads to low-level inflammation, we may be able to avoid at least some of that inflammation before it leads to or worsens disease.

What Happens in the Body When You’re Stressed?

When you’re stressed — emotionally, psychologically, or physically — your body goes into what’s colloquially called the “fight-or-flight response,” as it readies for, well, fighting or fleeing. One effect is the release of the stress hormone cortisol, says Dr. Gupta. Cortisol works to suppress nonessential-in-an-emergency functions, like your immune response and digestion. Together with the release of other chemical messengers, the hormone fuels the production of glucose, or blood sugar, boosting energy to the large muscles, while inhibiting insulin production and narrowing arteries, which forces the blood to pump harder to aid our stressor response.

Another hormone, adrenaline, is also released, which tells the body to increase heart and respiratory rate, and to expand airways to push more oxygen into muscles. Your body also makes glycogen, or stored glucose (sugar), available to power muscles. In addition, stress decreases lymphocytes, white blood cells that are part of the immune system, putting you at risk for viral infections like the common cold.

“When the fight or flight response is invoked, your body directs resources away from functions that aren’t crucial in life-threatening situations,” Gupta says.

The fight-or-flight response itself is meant to be short term and adaptive, which makes sense: When your body goes into that mode, your normal immune function is temporarily shut down. If you think of fight-or-flight as triggered by something like a tiger chasing you, your body devotes energy and resources to running away, not to digesting the last thing you ate — or to sending immune-fighting cells to kill a cold virus. It’s when you’re in that state chronically that the cascading inflammatory response is set up.

It’s this maladaptive response to stress, says Gupta, that over time perpetuates itself and becomes implicated in chronic health problems.

What Is Inflammation?

Inflammation is the body’s response to a threat, whether it’s a foreign invader like a bacteria or virus, cancer, a transplanted organ (which the body sees as “foreign”), or even a psychological or emotional stressor. In response, the immune system sends out an army of chemicals, called pro-inflammatory cytokines, to attack the invaders.

“Think of inflammation as a ‘sickness behavior,’” says Madhukar Trivedi, MD, director of the Center for Depression Research and Clinical Care at UT Southwestern Medical Center in Dallas. Inflammation, he says, “causes your body to act fluish, even in the absence of the flu virus.”

Pro-inflammatory cytokines usually do their job and then disappear, but when stress is chronic, they are “upregulated” in your system — meaning the cycle of stress and inflammatory response gets habituated in the body, explains Gupta. Over time, these cytokines may perpetuate themselves. That’s when inflammation starts to cause deleterious effects on the body. And while no one is completely sure why — there are many mechanisms responsible for diseases — what many conditions have in common is chronic, low-level inflammation.

Chronic Conditions Linked to Stress

• Rheumatoid Arthritis (RA) It’s understood that inflammation is behind RA, a disease in which the body’s immune system attacks joints and tissues, causing stiffness and pain. Over time, inflammation can damage joints and bones, causing abnormalities. Inflammation in RA is partly caused by cytokines, chemicals that are released by stress. So if you’re stressed you’ll release more of these chemicals, increasing the amount of inflammation in your body. It may also be the case that the inflammation associated with RA can lead to other medical issues, such as heart attack,  stroke, or even cancer, according to research. Researchers concluded that the inflammation that caused the RA, plus further inflammation caused by the RA, may be the culprit.
• Cardiovascular Disease An amped-up sympathetic nervous system — the response that primes your body to fight or flee — also works to constrict blood vessels, which forces your heart to work harder and raises blood pressure. Inflammation is at the core of the development of atherosclerosis, a precursor to heart disease, says Gupta. In addition, those who are chronically stressed tend to make unhealthy choices (such as eating unhealthy foods, smoking, and not exercising) that contribute to or worsen cardiovascular disease.
• Inflammatory Bowel Disease (IBD) IBD is an umbrella term for inflammation-linked conditions that affect the gastrointestinal system, including Crohn’s disease and ulcerative colitis. Both are exacerbated by stress, which affects the body’s normal secretion of digestive enzymes, and can interfere with how you digest food, absorb nutrients, and rid the body of waste. In recent years, researchers have linked a peptide in the brain and gut called corticotropin-releasing factor (CRF), which is activated when you’re stressed, to proper colonic function. In addition, one study stated that CRF plays a major role in bowel function, and may help explain the link between stress and irritable bowel syndrome (even though IBS isn’t a form of IBD).
• Depression Pro-inflammatory cytokines, those chemical messengers released in response to physical or psychological stress, can trigger depressive symptoms in some people, leading to lowered mood, fatigue, and lack of normal enjoyment of life. “Inflammation can lead to symptoms that look like depression, and in people who already have depression, inflammation can worsen the symptoms,” says Dr. Trivedi. In one study, researchers subjected mice to stressful conditions while monitoring signs of brain immune cell activation. In this study, anxiety and depression-like activity were associated with activation of the immune cells within the brain. This suggests that exposure to stress leads to the rewiring of neural circuits in the brain, setting off of mood symptoms.

Strategies to Reduce Stress and Decrease Inflammation

There are many research-backed ways to reduce stress, chief among them aerobic exercise, yoga, and meditation.

One study found that subjects who meditated regularly had lower levels of cortisol, as measured after a social-stress test. Meditators also had a less-pronounced inflammatory response in their bodies. Similar results have been linked to the regular practice of yoga, which another study found lowered levels of cortisol and decrease inflammation.

Although the same stress-reduction method might not work for everyone, Gupta says that every form of stress reduction does require patience.

“We essentially have to learn how to change our response to situations in our environment — responses that may have evolved over decades of our lives,” she says.

Other stress relief techniques include:

• Journaling
• Talking with a friend
• Walking in the park or forest
• Breathing in lavender or scented candles
• Counseling and therapy

Taking time to be outdoors, in nature, and with other people — the opposite of some of our work-focused, isolated, and sedentary modern lifestyles — works wonders to reduce stress, Gupta says. “They create space between our environment and ourselves, so we have some room to respond rather than to react.”