Stress and negativity can do a number on our immune system. They can boost our chance of getting infections, slow down the healing process, increase inflammation and even speed the growth of some cancers.

The good news is, just as negative emotions can impact our ability to fight disease, a positive outlook can bolster our immune response, explains Esther Sternberg, MD, author of Healing Spaces: The Science of Place and Well-Being. According to Dr. Sternberg, the neurotransmitters that the body releases when we’re happy, like serotonin and dopamine, enhance healing.

“If you’re having happy thoughts, your brain processes them in a way that dampens the fight-or-flight output of the nervous system,” says Thomas Morledge, MD, of the Center for Integrative Medicine at the Cleveland Clinic. In layman’s terms: The chemicals that your brain releases tell the nervous system (which is responsible for your stress response) to take a chill. “If you’re able to diminish the stress response, you’ll heal better,” Dr. Morledge says.

Don’t Worry, Be Healthy
So, can an upbeat attitude and healthy lifestyle prevent disease? That depends. “Most complex diseases have many genes that determine if you’ll get it,” Dr. Sternberg says. “There are 20 regions of chromosomes that contribute to whether or not you will get inflammatory arthritis, for example. If you inherit all of them, there’s probably not much you can do to change the fact that you’re going to get it. If you inherit five or 10, then the environmental factors become much more important in determining if you’re going to get the disease and when you’re going to get it. And one of the factors that contributes to developing some of these diseases is chronic stress.” She cites patients with lupus who didn’t develop symptoms until after going through a divorce or losing a spouse. What’s important to remember is that no matter what genes or disease you have, you can always improve your ability to heal.

That’s why keeping your stress levels in check is so important. According to a study in the journal Psychosomatic Medicine, when someone loses their job, their immune system weakens. But when the stress is gone — presumably because they found another job — the immune system can bounce back.

Mind Over Matter
The brain communicates with our immune system via the vagus nerve, which extends from our brain to our gut. This nerve relays information about the state of the body’s organs back to the brain so the brain can keep all systems regulated. The vagus nerve can lower heart rate and blood pressure, regulate our stress response and sense inflammation and suppress it. By learning how to control our vagus nerve, we may be able to stop excessive inflammation. That’s where meditation comes in.

Because negative emotions increase the production of inflammatory cells, meditation can help counter the effects of stress on the immune system. “You’re taking away those negative stress hormones that suppress the immune system, and you’re boosting other positive pathways in the brain, so the activation of these chemicals that are released actually boost the immune system,” Dr. Sternberg says.

A 2008 study at UCLA showed that an eight-week mindfulness meditation program called mindfulness-based stress reduction (MBSR) slowed the progression of HIV, while a study at the University of Wisconsin found that meditation could also influence our susceptibility to the flu. While MBSR usually involves 45 minutes to an hour of meditation a day, researchers at Duke University Medical Center found that 15 to 20 minutes of meditation twice a day can significantly reduce stress.

If meditation isn’t your style, try tai chi, a Chinese martial art that is more like yoga than kickboxing. Tai chi, a mind-body practice that involves a series of slow, fluid movements, has also been shown to improve immunity. Exercising regularly, spending quality time with family and friends, and getting enough sleep can also help bring your stress levels down. “Anything that increases your mood is going to have a positive effect on your immune system,” Dr. Morledge says.