In a year marked by a pandemic, economic downturn, race unrest and an election that culminated in a crowd storming the Capitol, we have faced stressors we could never have imagined before 2020. The causes and health consequences of stress have been widely discussed, as well as a host of tools to address the increasing anxiety we feel in our daily lives. But cortisol, one of the body's main steroid hormones, at the helm of our stress response, remains largely a mystery. Is our fight-or-flight response really connected to our prehistoric ancestors? Has our modern world evolved beyond the obsolete workings of our endocrine system? Here's what we know.
A caveman instinct?
Cortisol, along with adrenaline and norepinephrine, activates the body's sympathetic nervous system and causes a series of physiological responses that speed up breathing, constrict blood vessels, dilate pupils, and slow down the digestive system. It's called one fight or flight response, and it allows muscles to react more forcefully and move faster, preparing us to, well, fight or flight. Alan Goodman, a biological anthropologist at Hampshire College in Amherst, MA, studies stress in prehistoric humans. He agrees that cortisol and the entire acute stress response system is an evolutionary design.
"It's an old mammalian system that has been modified to protect hunter groups," says Goodman.
Still, it's hard to get a look at prehistoric people's daily stress levels because we can't look at their blood, he says, and cortisol is not very stable. Research published in the International Journal of Paleopathology, looked at the build-up of cortisol in the hair of 2,000-year-old Peruvian mummies and found "repeated exposure to stress." Another little pilot study of the same population found that hair samples suggest social, physiological and environmental conditions that are "strongly influenced by stress levels." But the research, Goodman says, has its shortcomings. The study authors cannot rule out chemical changes in the samples over time, and we are not sure how the buildup in the hair matches that of the blood.
Goodman prefers to look at skeletal indicators of prehistoric stress, because cortisol production can also affect the metabolism of bones and teeth. He studies ancient populations in the Illinois River Valley from about A.D. 1200, during the transition from hunting and gathering to agriculture.
"The enamel on the teeth grows like an onion and you can tell from the layers of the teeth in which years the body was stressed," says Goodman.
His research shows a stress response likely triggered by the shift from hunting and gathering to building civilizations and establishing a society.
"Life gets more complicated because social structures have a hierarchy," he says
With the haves and have-nots, the winners and losers, the stress becomes more complicated, no longer limited to immediate threats. Goodman sees this in his teeth when people build societies under executives.
Although enamel stops growing once permanent teeth develop, it is a growth stunt, known as enamel dysplasia, is frozen in time. Like the rings of a tree, you can see the years when life was stressful. Again, according to Goodman, this is an imperfect model, as infection and malnutrition can also affect enamel production. But after spending his career studying these populations, Goodman suspects it's likely a combination of all three. He says it's clear that stress has been around since the beginning of time, but today our response has gotten longer and in some cases, maladaptive
Chronic disease and cortisol production
In ancient populations, high cortisol levels meant good health, basically indicating that a human could still compete for survival, but in modern populations it can spell disaster. Sudha Seshadri, professor of neurology and founder of the Glenn Biggs Institute for Alzheimer's & Neurodegenerative Diseases at the University of Texas Health Science Center in San Antonio, studies the link between neurodegenerative diseases and high cortisol levels. Cortisol levels, she says, should vary throughout the day, highest in the morning when we are most active and lowest late at night when we should be sleeping. If levels don't vary or are too high in the morning, cortisol production can begin to affect other parts of the body.
"Chronic activation of fight or flight can cause problems in certain areas of the brain," says Seshadri.
Her Research published in the magazine Neurology, has shown that people with higher morning cortisol levels have more problems with parts of the brain responsible for memory retention, such as the hypothalamus, which may be an early indicator of dementia and Alzheimer's disease. Chronically high levels of cortisol have also been linked to high blood pressure, heart disease, anxiety and depression.
Lowering cortisol levels
People respond to stress with varying degrees of cortisol activation, Seshadri says, based partly on genetics and partly based on life experiences. "Hyper-activation" of fight or flight, especially during early childhood, is associated with exaggerated responses to stress later in life.
“It's a vicious cycle, the more you are exposed to stress, the more likely you are to overreact to it,” says Seshadri.
For parents, monitoring responses to stress can have lifelong consequences for children. Studies also suggest that meditation appears to lower cortisol levels, just like biofeedback, a technique that controls heart rate, breathing, brain waves, muscle contractions and perspiration and allows patients to respond to cues of the moment, build awareness and slow their stress response. In addition, practice generates its own positive chemicals to counteract cortisol such as dopamine, norepinephrine and serotonin.
Both Goodman and Seshadri agree that fight or flight occurs in both modern and prehistoric populations. But it is meant to help people respond quickly to a physical threat and then laugh at death later, not stumble all night over a perceived danger that never happens.
"The problem with humans is that we are symbolic beings, constantly finding meaning in situations where there was none," Good man says.
Experts argue that cortisol still plays an important role in keeping us safe in our modern world. But the key is to temper your response once the threat is lifted, rather than constantly fearing the imagined saber-toothed tiger looming around the corner.