Immune health describes the immune system’s ability to heal and preserve bodily function when confronted by infection, injury (wound healing), and even malignancy. Our body relies on multiple levels of defense. These levels include physical barriers (skin and mucous membranes), inflammatory response inflammation, cellular response, and cellular adaptation.^[1] Moderation and balance in these different levels of defense are key to optimal immune health. When the immune response is inadequate, this can open the door for infection by harmful pathogens. In contrast, an overzealous immune response could break tolerance of the immune system to ‘self’ molecules in the body, resulting in autoimmune disease. When it comes to immune health, balance is the key.^[2]

Healthy immune response includes the ability to accurately determine what is harmful to the body, adapt to changes in the environment, manage infections, and retain memory of what foreign cells cause damage.^[2] One approach to quantifying immune health is by measuring biomarkers in blood that reflect each of these facets of the immune response. These biomarkers may include: leukocytes, lymphocytes, cytokines, T-cells, natural killer (NK) cells, monocytes, C-reactive protein, and antibodies. An important consideration here is that these biomarkers may be elevated as part of a healthy immune response, for example, to an infection. Concern may be warranted if there is an abnormally high level of inflammatory biomarkers or if they’ve been circulating at a higher than average level for an extended time.^{[3] [4]}

Beyond blood tests, perceived immune status is a subjective assessment that may be more accessible to those outside of the clinical setting. The Immune Status Questionnaire (ISQ) was published in 2019, and is a validated self-assessment that may help individuals determine if they should seek medical attention, make lifestyle changes, or take further action to improve immune health.^[5]

Current research suggests that when it comes to exercise for immune health, moderation, balance, and consistency are key. Moderate exercise has been shown to have numerous benefits on immune health. Although physical activity is a stressor that does incite an immune response, the degree of the immune response and whether it’s harmful or helpful to immune health can be situationally dependent.

The current understanding is that consistent, moderate to vigorous intensity exercise (<60 minutes in length) is beneficial for immune health and can enhance adaptive immunity, thereby improving protection from community acquired illness and increasing the efficacy of vaccines.^[6][7] Muscle contraction is also beneficial to immune health by releasing helpful immune mediators, aiding in lymphatic drainage of waste products, and possibly even diversifying the gut microbiome.^[1][8] On the other hand, extreme exercise (especially in the untrained) can be detrimental to immune health. When healing from extreme exercise, the immune system becomes preoccupied and can devote fewer resources to defense.^[9]

The effects of many supplements on immune health markers have been studied, and the research is ongoing. As of 2022, some of the most frequently studied supplements for immune health include Fish Oil, Vitamin C, Colostrum, Spirulina, Astaxanthin, Reishi, Vitamin D, Vitamin E, Boron, Conjugated Linoleic Acid, and Garlic. Many of these supplements have been studied for their ability to improve immunity by limiting inflammation or by enhancing the body’s defense against damaging compounds, such as free radicals. Two exceptions to this list are Vitamin D and Garlic, both of which are primarily known for their ability to help the body manage or resist infections. A group of supplements that individually have been studied to a lesser degree on this topic, but that collectively present a noteworthy body of evidence, are adaptogens. Adaptogenic plants (such as Eleuthero, Ginseng, Ashwagandha, Rhodiola rosea, and Astragalus) are thought to work primarily through their ability to help the body adapt to stress.^[10]

Diet can impact most physical functioning, so it’s no surprise that it can also play a role in immune health. Similar to the ways supplements have been studied, the focus has been on the ability of nutrients to either reduce susceptibility to infection or to enhance healing through modulating inflammation and oxidation. Current research suggests that when part of the diet, plant-based compounds such as flavonoids may reduce incidence, duration, and severity of upper respiratory infection.^[11] Foods like blueberries and grapes tend to be high in flavonoids (anthocyanidins and flavonols), which have antioxidant properties that may enhance immune health. Beyond flavonoids and their antioxidant capacity, complete plant-based diets, such as the Autoimmune Protocol and vegan diets, are full of phytochemicals, fiber, vitamins, and minerals, all of which can contribute to immune health.^[12] Alterations in the gut microbiome may also play a role in immune health,^[13] which could explain why diets that include probiotic-rich foods, such as Kefir, have potential immune-enhancing effects

Stress exposure, sleep, and metabolic health all have both distinct and overlapping effects on immune health. Sleep has a profound effect on the immune system, and consistently getting enough of it can improve the ability to fight off infections (or avoid them altogether) and increase the efficacy of vaccines.^[14] Excessive stress (either psychological or physiological) can have positive or negative effects on immune health, depending on the type of exposure. For example, temporary stress from exercise or public speaking can have positive effects on immune health,^[15] while chronic stress exposure can impair immune health by limiting the ability of the immune system to fight off infections and/or increasing the risk of autoimmune disease.^[16] Metabolic health — in particular the ability of the body to regulate blood sugar levels — also plays a significant role in immune health, since impaired blood sugar control and insulin resistance have widespread negative effects on the immune system.^[17]