“Happiness is not a matter of intensity but of balance, order, rhythm and harmony.”
-Thomas Merton, American Trappist monk, mystic poet, and social activist
“There is no doubt that when you take it to the next level, the mind and the body are connected, and that when those connections are intact and in balance you have health and when they’re broken you have disease.”
-Esther M. Sternberg, M.D., Professor of Architecture, Landscape Architecture and Planning, University of Arizona
Enhancing one’s immune system’s defenses against foreign invaders (germs) is an important but complex topic. Yet, almost every week, I read an article by someone who claims to have discovered the key to boosting one’s immune system. In this week’s Germ Gems post, I provide my assessment of these claims.
Concept of homeostasis. The immune system functions like a well-tuned orchestra. This idea is not new. Instead, it can be traced to two giants in the field of physiology: the French scientist Claude Bernard and the Austrian-born Canadian endocrinologist Hans Selye.
Both scientists set the stage for thinking of the role the immune system plays in providing physical and emotional harmony. In 1849, Bernard introduced the concept of homeostasis—a balance of the body’s internal environment. In 1936, Selye introduced the concept of stress into medicine.
Recap of the immune system. Innate and adaptive immunity are considered the main sections of the immune system orchestra. The innate immune system is composed of phagocytic cells (neutrophils and macrophages), NK cells, and their products; the adaptive immune system of T cells, B lymphocytes and their products. Last week, I discussed both in my Germ Gems post, “New Approach to Antimicrobial Resistance: ‘Stimulate the Phagocytes.’” But, I didn’t mention two relatively newly recognized sections of the immune system orchestra—the central nervous system (the brain and spinal cord) and the gut microbiome.
The brain is the most complex organ of the human body. It contains its own immune cells—macrophages called microglia—and it also regulates functions of the body’s immune cells through what is referred to as the Brain-Immune Axis. Like the brain, the gut microbiome regulates immune responses in a bidirectional manner. Simply put, the microbiota in the gut talk to the brain and the brain talks to the gut microbiome.
How to boost your immune system. If you want to boost your immune system, get vaccinated. Vaccines boost the adaptive immune system. The scientific results of numerous randomized clinic trials show that vaccines are highly effective and provide the best protection against many serious infectious diseases, e.g., smallpox, polio, measles, and COVID-19, to name just a few.
Most other recommendations on how to enhance your immune system are not backed scientifically by results of randomized clinical trials (probably in no small part because of considerations like, who would fund such studies?). Nonetheless, an Internet search for ways to boost your immune system is replete with recommendations from reputable sources. For example: the Centers for Disease Control and Prevention has the article “Six Tips to Enhance Immunity”; Columbia University Irving Medical Center provides “What You Really Need to Do to Boost Your Immunity”; Harvard Health publishes “How to boost your immune system”; and WebMD posts “13 Tips to Strengthen Your Immune System.”
In summary, these institutions recommend: (1) get current with your vaccines; (2) eat a nutritious diet; (3) stay physically active with walks and exercise; (4) don’t smoke; (5) drink less alcohol; (6) sleep for at least seven hours a night; (7) build your social network; (8) look on the bright side, laugh often; (9) engage with the arts; and (10) reduce stress. While most of these recommendations aren’t backed by scientific evidence, they do target the brain and gut microbiome and seem quite reasonable.
Because of the longstanding interest of my University of Minnesota Neuroimmunology Research program in the bidirectional interactions between the brain and the immune system, my favorite recommendation is to “reduce stress.” As a physician scientist, I was often struck by the more robust interest of my colleagues in veterinary medicine in the impact of stress on health. For me, one of the most telling experiments that supports the hypothesis that stress impairs immunity came from these researchers.
They demonstrated that when injured birds of prey (eagles, owls, and hawks) were confined in a raptor center, they often died of disseminated aspergillosis, a fungal infection that occurs almost exclusively in immunocompromised hosts, especially neutropenic hosts. And the veterinary medicine researchers discovered the underlying mechanism for the death of the raptors—impairment of the birds’ heterophils (equivalent to neutrophils in humans) due to what they called “captivity stress.”
I certainly am not an expert in “stress reduction.” But following the lead of birds seems worth considering—exercise outdoors regularly. And, whenever possible, invite a friend along to stimulate your conversation as well as your immune system.