Stress and Disease

by National Institute of Health

For thousands of years, people believed that stress made you sick. Up until the nineteenth century, the idea that the passions and emotions were intimately linked to disease held sway, and people were told by their doctors to go to spas or seaside resorts when they were ill. Gradually these ideas lost favor as more concrete causes and cures were found for illness after illness. But in the last decade, scientists like Dr. Esther Sternberg, director of the Integrative Neural Immune Program at NIH's National Institute of Mental Health (NIMH), have been rediscovering the links between the brain and the immune system.

The Immune System and the Brain

When you have an infection or something else that causes inflammation such as a burn or injury, many different kinds of cells from the immune system stream to the site. Dr. Sternberg likens them to soldiers moving into battle, each kind with its own specialized function. Some are like garbage collectors, ingesting invaders. Some make antibodies, the "bullets" to fight the infectious agents; others kill invaders directly. All these types of immune cells must coordinate their actions, and the way they do that is by sending each other signals in the form of molecules that they make in factories inside the cell.

"It turns out that these molecules have many more effects than just being the walkie-talkie communicators between different kinds of immune cells," Dr. Sternberg says. "They can also go through the bloodstream to signal the brain or activate nerves nearby that signal the brain."

These immune molecules, Dr. Sternberg explains, cause the brain to change its functions. "They can induce a whole set of behaviors that we call sickness behavior. . . . You lose the desire or the ability to move, you lose your appetite, you lose interest in sex." Scientists can only speculate about the purpose of these sickness behaviors, but Dr. Sternberg suggests that they might help us conserve energy when we're sick so we can better use our energy to fight disease.

These signaling molecules from the immune system can also activate the part of the brain that controls the stress response, the hypothalamus. Through a cascade of hormones released from the pituitary and adrenal glands, the hypothalamus causes blood levels of the hormone cortisol to rise. Cortisol is the major steroid hormone produced by our bodies to help us get through stressful situations. The related compound known as cortisone is widely used as an anti-inflammatory drug in creams to treat rashes and in nasal sprays to treat sinusitis and asthma. But it wasn't until very recently that scientists realized the brain also uses cortisol to suppress the immune system and tone down inflammation within the body.

Stress and the Immune System

This complete communications cycle from the immune system to the brain and back again allows the immune system to talk to the brain, and the brain to then talk back and shut down the immune response when it's no longer needed.

"When you think about this cross-talk, this two-way street," Dr. Sternberg explains, "you can begin to understand the kinds of illnesses that might result if there is either too much or too little communication in either direction."

According to Dr. Sternberg, if you're chronically stressed, the part of the brain that controls the stress response is going to be constantly pumping out a lot of stress hormones. The immune cells are being bathed in molecules which are essentially telling them to stop fighting. And so in situations of chronic stress your immune cells are less able to respond to an invader like a bacteria or a virus.

This theory holds up in studies looking at high-levels of shorter term stress or chronic stress: in caregivers like those taking care of relatives with Alzheimer's, medical students undergoing exam stress, Army Rangers undergoing extremely grueling physical stress, and couples with marital stress. People in these situations, Dr. Sternberg says, show a prolonged healing time, a decreased ability of their immune systems to respond to vaccination, and an increased susceptibility to viral infections like the common cold.

About the Author

NIH is the nation's medical research agency - making important medical discoveries that improve health and save lives. The National Institutes of Health (NIH), a part of the U.S. Department of Health and Human Services, is the primary Federal agency for conducting and supporting medical research.