Claire Johnson

Learning enthusiast and biology nerd

July 6, 2018

The science behind: Stress

Many of us feel stress on a regular basis, whether it be weekly, hourly, or daily. In fact, roughly 80% of Americans are stressed out, with employed adults around the age of 50 feeling the most stress. This stress doesn’t only affect how you feel, but also how your body works.

Like all emotions, positive or negative, stress levels can have a big impact on your body and health.

Read on to discover what effect stress has on your body, and what you can do about it.

Stress in the nervous system

Both positive and negative emotions affect our bodies more than we think, because mental health and biological health are fundamentally connected. Understanding stress from a biological standpoint starts with the nervous system.

The nervous system has two main branches: the central nervous system, which includes the brain and the spinal cord, and the peripheral nervous system, which consists of all the nerves that branch off from the central nervous system and are found elsewhere in the body. The peripheral nervous system is divided into the somatic nervous system, which controls voluntary muscle movements, as well as the autonomic nervous system, which regulates non-voluntary bodily functions like your digestion, your heart rate, and even the dilation of your pupils.

The autonomic nervous system is made up of the sympathetic and parasympathetic nervous systems, which are responsible respectively for the ramp up and cool down of the stress response.

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Stress in the body

When you feel stress, your body releases the hormones adrenaline and cortisol to trigger the fight or flight response, governed by the sympathetic nervous system. The sympathetic nervous system then causes:

  • Pupil dilation
  • Redirection of blood flow to your muscles and brain
  • Increased heart rate
  • Accelerated breathing
  • Suppression of less vital functions like your digestion and immune system

All of this activity enables you to use all your available energy to react to the stressor. This stress reaction is also known as the “fight or flight” response.

When the immediate stressor is gone, the levels of adrenaline and cortisol in your bloodstream decrease. This is when the parasympathetic nervous system kicks in to calm you down. It normalizes your breathing and heart rate, and refocuses energy on other functions like digestion and immune function.

Activating the stress response through the sympathetic nervous system and calming down through the parasympathetic nervous system is all dependent on the levels of cortisol and adrenaline in your bloodstream.

Stress in the long term

Stress is natural. Short lived stress is a good thing because it makes you energetic and alert when you need to be, like if you’re in the middle of the woods and need to outrun a bear. Your fight or flight response might save your life in that situation.  

But the sympathetic nervous system is not supposed to be activated for long periods of time. Feeling stressed for hours every day, for months at a time means that you have cortisol coursing through your body constantly, engaging your fight or flight response for prolonged amounts of time. Thus, chronic stress causes a whole host of health problems.

1. Weight gain

Your autonomic nervous system controls your digestion. When you feel stress, your sympathetic nervous system, or your “fight or flight” response, suppresses your digestion. In the short term, this makes you feel less hungry.

But as time stretches on, your digestion stays inefficient, and on top of that, your body thinks that you’ve just fought off that bear and that you need to replenish your energy storage in the form of fat. So even though you’re just sitting in a chair at work, your body will hang on to everything you digest, causing weight gain.

2. Heart disease

The fight or flight response redirects blood flow away from internal organs and toward your muscles and brain. One of those internal organs is the liver, which is responsible for filtering the cholesterol and fat out of the blood.

When blood is directed away from the liver, that cholesterol stays in your bloodstream, and leads to a buildup of saturated fat and cholesterol around your heart. That buildup increases the risk of heart disease by 40%, and can eventually clog an artery. Chronic stress actually increases risk of a heart attack by an alarming 25%.

3. Illness

Another result of arousing the nervous system is immune system suppression. Again, this is great in the short term for running away from that bear. In the long term, however, a suppressed immune system leaves you especially vulnerable to infection and disease. The immune system functions by creating white blood cells and antibodies to fight infection. When you’re stressed, the body has less capacity to identify and counter all of the threats to your health you encounter on a daily basis. In fact, stress is the basic cause of 60% of illness, and 3 in 4 doctors visits are for stress-related issues.

To understand more about how the immune system functions to keep you healthy and to fight disease when you’re sick, play the antibodies virtual lab.

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Ways to reduce stress

Reducing stress will not only keep your body and mind healthier, but will also help you live longer.

1. Breathing and meditation

Deep breathing exercises can help activate your parasympathetic nervous system, which controls the relaxation response.

There are several types of deep breathing exercises, but they share the common goal of breathing slowly and deeply, and making you more aware of and focused on your breath. Consciously slowing your breathing will also slow your heart rate, and will help cue the parasympathetic nervous system to take over and continue the calm-down process.

2. Physical exercise

Exercise is one of the best things you can do for your body in general and has the added benefit of decreasing stress. Find an exercise routine that you enjoy–hiking, yoga, swimming, or really anything–and stick to it, because exercising actually lowers levels of cortisol in your blood. Lower cortisol levels deactivates your sympathetic nervous system, reducing your biological stress response. Studies show that going to one exercise class can reduce stress by a drastic 26%. Exercise also improves your sleep, as well as releasing endorphins, which are chemicals that improve your mood.

Better yet, find a way to exercise in nature. Research shows that walking in the forest reduces heart rate, decreases sympathetic nervous system activity, and increases parasympathetic nervous system activity. In other words, walking in the forest can reduce stress and calm you down on a biological level.

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For the science behind building muscle and losing weight, check out our 3-step health guide.

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