This article appears in the October 2023 issue of Front Vision, an educational Chinese-language magazine for kids. It is reproduced here with permission.
How Stress Harms Your Health
by Kathryn Hulick
You’re walking to school when a large dog breaks free from its fenced-in yard and charges at you, barking loudly. Your heart pounds, you tremble, and with a burst of energy you didn’t know you had, you run away. This is the fight-or-flight response in action. It’s like a fire alarm in the body. Animals evolved this alarm system to help them survive in situations that could be life-threatening. When the alarm goes off, strength increases, senses sharpen, and pain lessens, making it easier to attack or flee. This all happens so quickly that you may react before you even realize you’re in danger.
Unfortunately, the body doesn’t always do the best job of detecting situations that are actually physically dangerous, like a dog attack. The alarm often goes off in response to difficult emotional situations, such as losing a sports game, struggling on a test, facing a deadline, running late, arguing with a family member, or lacking enough money. So the fight-or-flight response also has another name: the stress response. This set of bodily response can help you escape danger. But it can also be very harmful for your health, especially when you are stressed out a lot of the time. To study how stress impacts the body and long-term health, researchers often use animal models.
A Relay Race of Hormones
The stress response triggers the release of a cascade of chemical messengers. The alarm sounds when the brain first detects a possible threat or an emotional stressor. The brain immediately sends a message to the adrenal glands in the kidneys to release epinephrine (commonly called adrenaline). This hormone causes many changes in the body. It makes your heart beat faster, which helps blood reach the
organs more quickly. It also causes rapid breathing and makes airways in the lungs open up so that you can take in more oxygen. This extra oxygen goes to the brain, which becomes more alert. Vision, hearing, touch, and other senses sharpen.
If a stressful situation doesn’t get resolved quickly, the brain prepares to keep the body on high alert. This process takes place on a pathway called the hypothalamic-pituitaryadrenal (HPA) axis. It’s a bit like a relay race that starts in the brain, where the hypothalamus releases corticotropinreleasing
hormone (CRH). This hormone alerts the pituitary gland at the base of the brain to secrete another hormone called adrenocorticotropic hormone (ACTH). ACTH completes the next leg of the relay when it visits the adrenal glands in the kidneys. These glands then release cortisol and other glucocorticoids.
Cortisol is considered the primary stress hormone. It increases the amount of sugar in the blood, which brings extra energy to the muscles. Cortisol also slows down bodily functions that aren’t essential to survival, including digestion, reproduction, and growth. Cortisol interacts with the brain as well, often associated with the memories of fear.
There are still more hormones involved in the stress response. Epinephrine is closely related to norepinephrine and dopamine. All of these chemicals belong to a group called catecholamines. They can act as hormones or neurotransmitters. That means they can cause changes in the body and brain. In the brain, they help manage your response to emotional stress. They can make you feel really good in
exciting or thrilling situations. But they can also make you feel anxious or irritable or make it difficult to sleep.
The stress response becomes especially harmful if it happens continually or regularly over a long period of time, circulating lots of extra cortisol throughout the body. Chronic stress is a disorder in which a person’s stress level remains high for a long period of time. Post Traumatic Stress Disorder (PTSD) is a type of chronic stress that results from experiencing a particularly terrifying or horrible event.
Chronic stress wreaks havoc on the mind and body. This became clear in the 1980s, when the Whitehall Study looked at the mortality rates of British civil servants aged 35 to 55 working in the London offices of
20 Whitehall departments, as well as the impact of occupation and work environment on health and disease, it discovered that servant with a lower grades were far more likely to die from heart problems and cancer. The study showed that job stress was linked to health.
Then in the late 1990s, psychologist Sheldon Cohen of Carnegie Mellon University led a study that showed that people experiencing chronic stress are more likely to fall sick when exposed to the common
cold. By 2003, researchers working with data from the Whitehall Study showed that stressful jobs where workers had very little control were linked to higher rates of heart disease for men and women. Chronic
stress also increases the likelihood of obesity, diabetes, hypertension (high blood pressure), arthritis, asthma, depression, addiction, and other disorders. It can even make cancer spread more easily.
Stress Messes with the Immune System
Why is chronic stress so harmful? Researchers are finally finding some answers. One important factor is inflammation. This is a normal part of the way the immune system works. Inflammation can help fight
off infection by pathogenic microorganisms. For example, when you skin your knee, the area around the wound turns red, hot, and painful. That’s inflammation. A fever is another example of inflammation in
action. The increased temperature kills some microbes. Except for these emergencies, inflammation can also happen at low levels inside the body over a long period of time. This type of inflammation can
damage cells, tissues, organs, and even genes. It can lead to disease.
Chemical messengers called cytokines trigger inflammation. Researchers can check a person or animal’s cytokine levels to find out how much inflammation they are experiencing.
In 2012, Sheldon Cohen, the psychologist who had demonstrated the link between stress and catching a cold, showed that the body can lose its ability to control inflammation when it experiences chronic stress. Cohen said, “Inflammation is partly regulated by the hormone cortisol and when cortisol is not allowed to serve this function, inflammation can get out of control.” Normally, cortisol tells the immune system to slow down or stop inflammation. But if cortisol is always flowing through the body, immune cells may learn to ignore it. “The cells stop paying attention,” Kathi Heffner, a psychologist at the University of Rochester in New York, told Science.
The way stress messes with the immune system matters for something as mundane as a wound healing. An unusual study from 2005 enlisted couples as volunteers. Each volunteer received a small blister on the arm. Next, the couples either underwent friendly counseling or had to recount arguments. The couples who were most hostile during the argument sessions had wounds that took two days longer to heal, on average. The area around their wounds also had lower levels of cytokines. Stress raises cytokine levels and inflammation throughout the body, so there were likely fewer of these messengers available to respond to the wound and alert the immune system that the area needed help healing.
Stress and Cancer
Chronic stress doesn’t cause cancer—but it can make the disease worse. A healthy immune system keeps cancer in check by attacking cancer cells before they spread too widely. When stress weakens the immune system, cancer gets a chance to grow out of control. A 2021 study of mice with breast cancer tumors found that exposing them to chronic mild stress made it more likely that their cancer would spread. The stressed animals also had higher levels of proinflammatory cytokines, indicating that chronic inflammation was one reason their immune systems couldn’t fight off the cancer.
In addition, the stress hormones norepinephrine and epinephrine seem to be able to fuel the growth of some types of cancers. One way they do this is by helping to build new blood vessels, which tumors need in order to grow. Norepinephrine and epinephrine get transmitted through the nervous system, and researchers have discovered that tumors link up closely with the body’s nerves. “The idea that tumors can be so controlled by these nerves—all of a sudden it really brings some clarity into why various types of stress can be so bad for people,” Elizabeth Repasky, a cancer researcher at Roswell Park Comprehensive Cancer Center in Buffalo, New York, told Science.
Genetic Changes
Even after a stressful period ends, the effects may linger. Many books and movies showcase a traumatic, stress-filled childhood as the reason for a character’s emotional or behavior problems later in life. There’s some truth to this. One way trauma can etch itself into the body and brain is through changes in the activity level of different genes. This is called an epigenetic change. It doesn’t alter the underlying DNA, but can change the types of instructions that DNA sends out to the body. And researchers have actually found epigenetic changes associated with various types of stress and trauma.
A 2010 study looked at epigenetic changes in mice. The researchers gave the mice a hormone that their bodies produce when stressed, then tested them for behavioral changes. They also checked how genes involved in the HPA axis (remember the relay race?) were getting expressed. They found that exposure to the stress hormone made the mice behave in a more anxious manner. Also, three genes involved in the HPA axis changed their expression. This might help an animal (or person) prepare for a similar stressful event in the future. James B. Potash of the Johns Hopkins University School of Medicine in Baltimore, Maryland led the research. “If you think of the stress system as preparing you for fight or flight, you might imagine that these epigenetic changes might prepare you to fight harder or flee faster the next time you encounter something stressful,” he said. But when the stressor is something emotional or psychological, the result may instead be depression or another mental disorder.
Stress and the Brain
Inflammation is another factor involved in how stress leads to depression. Normally, a blood-brain barrier acts as a shield to protect the brain from dangerous substances. But inflammation can weaken this shield. “So eventually, you will have some tiny holes in the blood-brain barrier,” Caroline Ménard, a neuroscientist at Université Laval and CERVO Brain Research in Quebec, Canada, told The Washington Post. “And this will allow inflammation to pass from the blood into the brain, and this will eventually change the neurons and all the cells that create the behavior and who we are.” When inflammation harms brain cells, this may lead to anorexia, lethargy, depression, or other issues.
Not all depression has the same cause – only about 30 percent of depressed people have higher than usual levels of inflammation. However, depressed people are more likely to have increased inflammation when compared with people who aren’t depressed. And drugs that increase inflammation in the body can cause depression as a side-effect.
Stress and the Gut
Stress also impacts the body through the gut. This may not be surprising, as many of the most common symptoms of stress involve gut troubles, such as heartburn, stomachache, queasiness and vomitting, diarrhea, or constipation. The gut is home to a huge population of teeny-tiny bacteria and other microbes. These make up the gut microbiome. Many of these microbes are helpful denizens of the body – they make it possible to digest certain foods and produce some kinds of vitamins. A balanced and diverse gut population is linked to strong health.
Though the gut is located way down near the bottom of the body, it is closely linked to the brain via a pathway called the gut-brain axis. When a person feels emotional or mental stress, messages travel along this axis to the gut. Stress disrupts the gut’s microbe population and can lead to an increase in harmful bacteria and a loss of helpful bacteria. However, the gut-brain axis also means that a person’s mental state can heighten gut health. Meditation or mindfulness practices can promote a healthy gut microbiome.
Healthy Stress?
Stress is a normal part of life, and small amounts of stress aren’t so terrible. In fact, some researchers have found that stress could even help make your immune system stronger in some cases. In a 2015 study on mice, researchers injected immune cells from stressed mice into mice that had immune systems that didn’t work very well. These mice began acting more social. “That was a surprise,” Miles Herkenham, a neurophysiologist at the National Institutes of Health in Bethesda, Maryland, told Science News. “We expected the cells to make the mice more anxious and depressed.” However, this effect only worked in mice that had received the stressed immune cell transplant and not in the original population of mice. These researchers think stressed immune cells could act a bit like a vaccine, teaching an immune system how to respond effectively to certain stressors.
A 2022 study on mice also found that stress could boost the immune system. These mice had inflammation in their colon. After one group of mice experienced 56 days of stress, their bodies were able to better resist further injury to the colon. “What we discovered it that chronic daily stress for six weeks was beneficial against a second injury. The mouse models that were stressed were actually protected,” said Fabio Cominelli, a gastroenterology researcher at Case Western Reserve University School of Medicine in Cleveland, Ohio.
While certain types of stress may have some benefits in certain situations, for most people, reducing stress is a path towards better health. If you experience a lot of stress all the time, then you should talk to a doctor or therapist and find ways to reduce your stress level. Your body and brain will thank you!
Sidebar: Sensation Seekers
Not all stress is bad. Adrenaline can heighten your senses or give you a rush of energy, which can feel really good. Plus, many situations that some people find stressful others find thrilling or exciting, like roller coaster rides, horror movies, or extreme sports. Psychologists call people who enjoy these types of experiences sensation seekers. Their bodies tend to release less cortisol and more dopamine in extreme situations. Dopamine is a neurotransmitter that is an important part of the brain’s reward system – it gets released when we anticipate a pleasurable or exciting experience. Sensation seeking behavior is also higher in teens and young adults. “There are lots of advantages to having some people in our society as sensation seekers,” Kenneth Carter, a psychologist at Emory University in Atlanta, Georgia, told NPR. “You know, these are people who work in emergency medicine, first responders, you’ll see them out helping with the rescue. And so, when they’re in those highly chaotic environments, they can focus, be organized and get stuff done.”