First off, many rush to try to boost the immune system only with certain foods or single nutrients, seasonally or when they feel sick. Admittedly, lacking one nutrient can throw off the immune system(1). However, as "studies continue to show that most diets lack [quite a few] vitamins and minerals, such as zinc and vitamin C, which play a special role in our bodies’ immune systems" and immune systems deal with invaders every day rather than at certain seasons or times, we really need to follow a nutrient-dense diet year-round that has maximum amounts of all sorts of nutrients(2). [Further, defeating E. coli, influenza, and such isn't the only object of supporting the immune system - ] such things as environmental toxins and stress can suppress the immune system(1).
- "Animal studies have found that deficiencies in zinc, selenium, iron, copper, folic acid, and vitamins A, B6, C, D, and E can alter immune responses."(1)
- Fiber (prebiotics) present in fruits, veggies, and other plant foods help keep up healthy gut microbes - and in turn these microbes "short chain fatty acids, which have been shown to stimulate immune cell activity." Probiotics contain living, probiotic (healthy) bacteria(1).
- Vitamin C, about the most famous nutrient for the immune system ever, has an antioxidant role. Note: "official" recommended daily allowances have been called in question as they have been geared to be enough to prevent scurvy but not enough for tissue saturation(2).
- Vitamin D is an immune system regulator(1) and balancer, acting like a hormone. There are receptors for it on B cell and T cells of the immune system(2).
- Zinc is tied to immune cell development and functioning, in particular T-cells. Immune systems without its antioxidant effects become compromised, even with a relatively minor deficiency(2).
References:
1. "Nutrition and Immunity." Harvard T. H. Chan School of Public Health: The Nutrition Source. The President and Fellows of Harvard College. Web. 16 Aug. 2021. https://www.hsph.harvard.edu/nutritionsource/nutrition-and-immunity/.
2. "7 Ways to Help Your Immune System Now." Isagenix Health. Isagenix Worldwide, Inc. 21 Oct. 2013. Web. 16 Aug. 2021. https://www.isagenixhealth.net/7-ways-to-help-your-immune-system-now/.