by Kevin Dervishi
figures by Tal Scully

You’re in the frozen goods aisle of the grocery store, surveying ice cream flavors. You’re cradling a bottle of wine–or maybe it’s a six-pack of beer. It doesn’t matter. Suddenly, someone down the aisle calls your name. It’s your recent ex, smiling and walking towards you arm-in-arm with their new romantic partner. This feeling is stress. It’s the feeling when you’re in a car accident on a busy street or frantically preparing the night before a critical exam or work presentation the following morning. It’s a familiar feeling: your heart beating faster. Your breath quickening. Your muscles tensing for fight or flight. It’s not always bad news of course–these physiological responses are also kicking in during good occasions such as when we’re exercising. But what does it mean for our health when the stress of accidents, exams, or exes extends beyond isolated incidents?

We’re currently facing the spread of coronavirus, the looming effects of climate change, and an upcoming presidential election in a divided political landscape (if I see another headline about a political poll I’m going to scream). It’s safe to say that Americans are going through a stressful time in early 2020. What does a stressful day, month, or year mean for us in the long-term? How does our mental state shape our bodies, and how do our bodies shape our mental state? These questions are important for our health and are ever-changing as the stressors of life in America–and our coping mechanisms for them–change over time.

Stress changes our behavior and long-term health

Everything you need to know about stress comes down to hormones. Three key hormones, in particular: cortisol, adrenaline, and noradrenaline. When our body is processing stressful messages from our mind (“exams/elections/deadlines ahead!”), it mainly uses these three hormones to respond. Adrenaline and noradrenaline are sister hormones with nearly identical structures that are both part of a short-term stress response. The levels of these hormones go up rapidly to initiate a quick fight-or-flight response, and go back down just as fast–in a matter of seconds or minutes. Cortisol, on the other hand, has a much slower and longer effect. Whereas adrenaline and noradrenaline levels spike in seconds to minutes, cortisol levels stay high for minutes to hours. In short, cortisol levels creeping higher is what you’re feeling during the slow build of suspense and fear during a horror movie, while hormones like adrenaline kick into gear right after a jumpscare in said horror movie (I’m looking at you, Pennywise).

The long-term effect of cortisol on our bodies

It has been known for several years that chronically high levels of cortisol can lead to a variety of health problems, such as diabetes and weight gain. What we may not appreciate is that these hormones also fluctuate over daily cycles, and the dysregulation of these cycles over days, months, and even years could be responsible for long-term health problems. Cortisol, for example, follows an interesting pattern: our body releases the highest levels of this hormone in the morning around sunrise. As our day goes on, our cortisol levels sink lower and lower. Once we fall asleep, they start to build back up again until peaking the next morning (Fig. 1). Although researchers are still debating the reason for this pattern, they have some ideas: the hypothesis most supported by published studies is that our body anticipates the stress of daily activities and increases cortisol levels to prepare for stressful activities. Once the day is over and we need to rest, our bodies prepare us by keeping cortisol levels low by bedtime. This is an excellent example of how our behaviors and mental state shape our physical state. More importantly, this cyclical nature is one of many reasons why an abnormal sleep schedule during crunch-time before a deadline can be detrimental to our body: it dysregulates the levels of important hormones like cortisol. Suddenly our body may produce peak amounts of cortisol at the wrong time, such as before bed the next day, and now one stressful situation has led to new one: your body is refusing to cooperate and go to bed!

Figure 1: Cortisol follows a daily rhythm. Our bodies produce cortisol based on a daily cycle of high levels in the morning, and lower levels in the evening. Sleep is a critical time where our bodies regulate the levels of cortisol (and stress) we feel.

The short-term effect of adrenaline & noradrenaline on our bodies

Although cortisol gets a lot of press, even short-term stress responses can have long-lasting consequences! A study published in 2018 suggests excess noradrenaline “can contribute to arterial hypertension and predisposes to cardiovascular and renal damage.” More recently, a groundbreaking study suggested that stress is a direct cause of hair-graying, confirming an age-old suspicion. The culprit was found to be one of the three hormones we just discussed: noradrenaline, which is released from nerves that over-activate under short-term stress. Our hair follicles have stem cells that create all the cells in the follicle, including pigment-producing cells, and these stem cells have been shown to be regulated by the nervous system. This study examined mice under three different stress tests to show that these stem cell populations become depleted in response to the nervous system releasing noradrenaline, leading to a permanent loss of pigment and resulting in gray hair/mouse fur. As we discussed earlier, noradrenaline release is one of the main ways your body immediately turns on a stress response in the face of intensely stressful situations, and this appears to be an unfortunate—but fascinating—side effect.

Our behavior can change our stress–for better or worse

It’s clear at this point that stressful situations and stress-related hormones have important consequences for our short-term feelings and long-term health. What we are only just now beginning to appreciate is how newer common behaviors such as smartphone use can affect our stress levels. Studies have shown that extended smartphone use correlates with elevated cortisol levels, which is a problem when you consider that the average American spends several hours on their phone every day. Although researchers have yet to disentangle whether smartphone use is directly responsible for a stress response, the established connection between the two should give us pause. 

Similarly, our engagement in social media and politics has been compared to sugar intake: healthy in small amounts, but stressful in the large amounts most of us have been experiencing over the last decade. A study published in 2018 found that test subjects randomly assigned to abstain from Facebook use for 5 days experienced lower cortisol levels, adding to a growing body of work examining social media and mental health. As for political engagement, a survey published in the journal PLOS One last fall found that almost two in every five Americans they surveyed reported being stressed by politics, while almost one in five reported losing sleep because of politics. People who frequently discussed politics and who reported being more involved in politics had the biggest increase in stress levels and other negative feelings.

All is not lost, however! Although our behaviors and habits can increase chronic stress levels, they can also do the opposite: practices such as meditation and mindfulness hold up under scientific scrutiny as treatments for psychological stress. Although stress levels have been rising nationally, the popularity of strategies such as mindfulness, meditation, and yoga has increased. Whether or not that popularity is in response to rising stress levels remains to be seen; regardless of its driving force, this increased popularity is a positive development.

Figure 2: Stress and stress-related feelings are on the rise. Surveys of college-age students show a concerning national trend in young adults. As the prevalence and frequency of stressful feelings increase, so does the urgency for stress management techniques. Figure modified from a JAH publication.

Seeking out positive behaviors is more important now than ever: in the last decade alone, surveys have shown large increases in the rates of depression, anxiety, and suicide-related thoughts in college-age individuals (Fig. 2). By engaging in positive behaviors that reduce stress, we can hopefully buck the trend and be the masters of our stress levels–and not the other way around.

The takeaway: you’re in the driver’s seat

At the end of the day, the research illustrates a pretty remarkable path we take through stressful situations: your mind sits in the driver’s seat of the car that is your body. Through our feelings, behaviors, and responses, our body responds to stress or the lack thereof by revving up or shutting off the engines. Waking up in the morning is similar to turning the key in the ignition: it’s a normal and healthy revving of our systems. However, just as slamming the gas pedal and flooding your engine can damage your car, so can excessive stress. As the world around us grows stressful, it’s up to us to be cognizant and responsible drivers that can avoid damaging our vehicles by using our ever-increasing knowledge and mental health toolbox for any necessary repairs.

Kevin Dervishi is a PhD candidate studying cancer genetics in the Biological and Biomedical Sciences Program at Harvard Medical School. Opinions and additional work can be found on his twitter. He likes to think he is an expert on cortisol because he is frequently stressed.

Tal Scully is a second year Ph.D. student in the Systems, Synthetic, and Quantitative Biology program at Harvard University. You can find her on Twitter as @TalScully.

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