It may not surprise you that your immune health is directly tied to your gut health. After all, about 75% of your immune system is housed in your gut. What may surprise you, however, is that the digestive tract is technically outside of the body, even though we tend to think of it as an inside entity. It’s classified as such because its long, continuous tube communicates with—and has contact with—the outside world.
It takes a lot of guts to survive in this role, too.
In case you didn’t know, the digestive system is about 30 feet long, extending from the mouth to the other end, and has a lot to do with your immune health. It absorbs nutrients from food, of course, but it also serves as a barrier to unwanted invaders—much like the skin does.
There’s more to the GI tract and immunity, though. White blood cells, or leukocytes, can be found under the tonsils near the top of the digestive tract. (White blood cells, by the way, are part of the body’s first line of defense against invaders.) Likewise, the small intestine contains something called Peyer’s patches that are made up of lymphatic tissues that are also brimming with white blood cells. And let’s not forget about the walls of the large intestine. They’re covered with protective immune modulators.
A healthy diet—which directly affects the gut—has also been linked to immune health. For example, one study found that mice whose diets are deficient in proteins have reduced numbers of and function of T cells and macrophages and also have reduced production of immunoglobulin A (IgA) antibody.
Micronutrient deficiencies in zinc, selenium, iron, copper, folic acid, vitamin A, vitamin B6, vitamin C and vitamin E may also adversely alter immune responses in animals. A similar thing can happen in people, especially the elderly. They are often at risk for micronutrient malnutrition, which occurs when a person is deficient in some essential vitamins and trace minerals. Researchers are looking further into the connection between nutrition and immunity in the elderly. Micronutrient malnutrition, by the way, is common for older adults—even for those who live in affluent countries. It’s not just a by-product of poverty; it’s nutritional fallout.
Along with proper nutrition, good bacteria called probiotics can positively affect immune system function. For instance, it’s known that certain good bacteria in the gut influence the development of the immune system, such as correcting deficiencies and increasing the numbers of certain T cells.
What’s more is that the GI tract itself is a lymphoid organ populated with lymphocytes, macrophages and other cells that participate in immune responses. Lymphoid tissue within the GI tract is called gut-associated lymphoid tissue or GALT and is distributed in three basic populations: Peyer’s Patches, Lamina propria lymphocytes and Intraepithelial lymphocytes.
Peyer’s patches are lymphoid follicles found in the mucosa of the small intestine, especially the ileum, and defend the gut against pathogens. They also serve to decide what is allowed in the gut (such as food elements) and what is not (such as harmful pathogens). B lymphocytes are found predominately in Peyer’s patches. Likewise, the lamina propria lymphocytes and intraepithelial lymphocytes serve to defend the gut, mostly turning into mature cytotoxic T cells to act against other assaults.
Microfold cells, or M cells, are also specialized intestinal epithelial cells that harbor lymphocytes and macrophages. They assist in that all-important process known as phagocytsosis—the process in which white blood cells track down and get rid of unwanted foreign cells or particles and destroy them.
That all may sound overwhelmingly scientific, but the bottom line is that it takes a lot of guts to maintain immunity.