'WITHTress has a well-recognized effect on your immune health, says Daniel M. Davies, head of the department of biological sciences at Imperial College London. “But stress is a very broad phenomenon. You may feel stressed watching a horror movie, or experience long-term stress such as going through a divorce.”
Short-term stress can temporarily affect your immune system. “The number of immune cells in the blood changes,” Davis says. “But things return to normal after about an hour, so it's unlikely to have any major impact.”
Long-term stress is a completely different story. When your body perceives a threat, the adrenal glands release hormones such as adrenaline and cortisol. They prepare the body for the fight-or-flight response by increasing blood pressure and heart rate, but also suppressing the immune system.
“We can see it even at the molecular level,” says Davis, author Self-Defense: A Myth-Busting Guide to Immune Health. “If we take immune cells and expose them to diseased cells, such as cancer, the immune cells will usually destroy them. But if we add cortisol, they become much less effective.” If exposure to stress hormones continues for weeks or months, our immune system will be weakened.
Practices such as mindfulness, tai chi and other stress reduction strategies have been shown to reduce cortisol levels, which should benefit the immune system. However, this is difficult to prove, Davis says. You can't ethically expose large numbers of people to a disease to test their immune response, and measuring “immune health” in real-world settings is difficult. “It’s also difficult because you can’t avoid stress,” he adds. “Every change in our lives will be accompanied by some stress, and many changes are positive.”
However, if you're concerned about long-term stress, Davis recommends talking to your GP.
