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Does stress block the feeling of pain?

    • A highly stressful situation can block an injured person from feeling pain
    • This phenomenon is called "stress-induced analgesia"
    • Exercise is a great way to reduce stress
  • Bottom Line: While stress can have beneficial effects in short-term situations, long-term stress can harm health
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Stress-induced analgesia occurs when an injured person can ignore pain because of another stressful situation.

Stress-induced analgesia occurs when an injured person can ignore pain because of another stressful situation.


Stress-induced analgesia occurs when an injured person can ignore the pain of an injury because of other stressful situations going on at the same time. For example, if you bang your shin while hiking, it stops hurting if you see a mountain lion. Researchers say a stress hormone, noradrenaline, also known as norepinephrine, which floods the bloodstream during stressful events, numbs the brain's pain-processing pathway. Previous studies have shown that adrenaline is also part of the reason that certain forms of stress can boost the immune system and help fight off the flu. A study on rats explains how someone injured in a car wreck can still manage to save other people.

Questions and answers

How does adrenaline work with stress?

Dr. Sanjay Gupta, chief medical correspondent: We've known for some time that adrenaline plays a part in reducing pain when we're in stressful situations. But this is the first time we've seen how the process works. For example, you cut your leg and see a grizzly bear at the same time. A stress hormone called noradrenaline will flood the brain, blocking its ability to produce pain.

Does this mean that being under stress can actually be good for you?


Certain kinds of stress can be good for you, especially those that involve social interactions. If you're a busy mom, and you're in the PTA, and you do community service, this can actually make you less susceptible to colds. Sometimes, things such as work deadlines and exams can boost your immune system as well. It works by triggering hormones that prepare the immune system for danger, helping the body fight off infections. But chronic stress can make you sicker -- especially people who may be caring for a sick relative, or are unhappy at work, or are in bad marriages. It can weaken the immune system and lead to diseases.

So how can we avoid the negative effects of stress?

The key to avoiding stress is exercise. Research has shown it's one of the best ways of relieving stress. Any activity that gets your heart pumping will get those endorphins flowing and make you feel better. Also important is good nutrition. When you get busy, it's tempting to skip meals or eat fast food - but that's a mistake. The body depletes its stores of nutrients when under stress. So it's important to eat balanced, healthy meals. Finally, you have to get enough sleep. It restores the body and mind and helps us fight off illnesses. Staying healthy under stress depends on a number of things -- genetics, the environment and your age. But you can help yourself by avoiding chronic stress. It's important to remember that no matter how much "good" stress you have, you can't fight a virus once it takes hold. So it's important to wash your hands often, avoid unnecessary contact, and keep surfaces clean.

CNN spoke with John Sheridan, Ph.D., professor of oral biology and associate director of the Mind/Body Center at Ohio State University and author of a study on rats called "Social Stress Boosting Immune System's Flu-fighting Abilities." Here are portions of that interview.

CNN: What about stress alleviating pain?

Sheridan: That's stress-induced analgesia. In recent years, we've been able to do things like PET scans and MRI studies. We can see what's happening in brain activity. There's a response within the brain related to production of opioids that dulls the pain.

There probably is an opioid component to what we're studying, but we don't know what that is yet. We were surprised to see that the animals had an enhanced response. We hope to take it to humans in the future.

CNN: Can this work in the long term?

Sheridan: That's what we're looking at, the longer-term health outcome. We can probably boost the immune system -- we haven't worked that out yet. It depends on the nature of the stressor and the nature of the individual responding to it. We talk about environment, genetics and the individual's immune system. It's a combination of various factors. There are people that are resilient, no matter what life throws at them. Healthwise, they don't seem to be affected the way long-term health caregivers are. It's genetics and environment. People who are going through an unstable marriage, are caregivers for a long time, people that are unhappy at work -- these kinds of long-term stresses seem to have a grinding affect on the immune system and gastrointestinal diseases. We tend to believe these kinds of stresses do make you more susceptible to infections.

CNN: How is the stress you get from bungee jumping different from social stress?

Sheridan: Bungee jumping is an adrenaline rush. A colleague named Sheldon Cohen at Carnegie Mellon did a study that shows susceptibility to infectious disease is diminished with the more roles you take on, the more social support. Those who have multiple roles, more social interactions, are less susceptible to colds. That's how we got into the social thing. If you happen to be a mother and you're involved in community service and you're in the PTA, you would think all of that would take away from your ability to fight disease. [Cohen] says the more social roles you have, the healthier life you live.

This is a holistic approach. We're working in mind-body interactions. We're really interested in how an individual's perception of their environment actually translated into their body or their physiology. We're interested in seeing if we can prevent suppression of immunity and perhaps enhance the immune system.

CNN: If you're sick, like you have the flu, and you're ignoring the symptoms and continuing to work, does that make you sicker because you're ignoring the illness?

Sheridan: Once the infection starts, once you've acquired the infection, most of what we talked about is not going to alter the outcome. The virus is going to win out. People with deadlines are usually people that can deal with those stressors. Those are short-term acute stressors...

Long-term chronic stress can make you sicker: a bad marriage, [being a] caregiver -- they tend to be suppressive. We're trying to figure out what's different about the aggressive interaction among the mice. We don't know what the long-term effects of social stress are.

CNN: Is there a difference in how the body responds to active and passive stress? What is the difference between these two?

Sheridan: They don't usually talk about active and passive stress. For a long time, they used the terms "acute" and "chronic." Acute is like exams and a work deadline, the body can deal with them fairly well. Some of them can enhance immunity. Chronic forms of stress are a bad job, a bad marriage. They tend to be health adversive. We're beginning to get a better handle on the nature of hormonal responses that occur in response to the stress.

CNN: Will this affect treatment options?

Sheridan: There can be drug-based therapies -- which is the goal of the folks doing this work. Once you've identified a certain pathway and release of a certain hormone, we can modulate that, to prevent some of the negative health consequences.

CNN: So is it all in the timing? If you experience acute stress, like a solider in Iraq, right before you're exposed to the flu virus, will that help you fight it off?

Sheridan: We don't know the answer to that. It's something we're looking at. The military is very interested in looking at that. There are forms of stress that might make them resistant. ... Adrenaline is a part of the response. When the animals fight, when you have a defeated response, they definitely activate adrenaline. We think that's a big part of modulating the immune system. It can have a positive effect.

CNN: There was small study on women that showed short bouts of mental or physical activity before getting the flu shot produced more antibodies.

Sheridan: They're enhancing the response to vaccination. ... People ask, how do you avoid stress' effects? One is exercise, nutrition and sleep. If you keep all those things in order, that's the best defense to enhance immunity. We did a study where we deprived people of sleep and vaccinated them. We found they made much less antibody. Folks in the UK and at the University of Illinois showed that if you put mice on treadmills and challenged them with the flu virus, they were much more resistant to infections. A healthy diet with all the appropriate trace minerals and vitamins is very important.

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