When we think of the immune system, we picture white blood cells working together to attack viruses, harmful pathogens, and antigens. While this is true, science is uncovering the whole story of the immune system and how it works, and a key component of that is in the gut.
We all know the warning signs of a weak immune system. Symptoms such as recurrent infections and lingering coughs and colds can all demonstrate that the body isn’t quite dealing with foreign bodies as well as it could. As well as this, repeated infections can damage the natural defenses of your body each time, compromising your ability to recover.
What proves challenging for general health and wellbeing is that there’s no catch-all way to strengthen the immune system, because it’s not a straightforward function.
The digestive system operates on its own self-held nervous system and holds a surprisingly vast influence over the rest of the body. Of course, by the time humans reach adulthood, the gut has become a delicate ecosystem containing trillions of bacteria, known as the gut microbiome. Significantly, it is one of the most complex systems known to biological science.
The system of signals and communication between the gut and the wider body functions means that the gut plays an integral role in developing and strengthening the immune system. The key is tackling what is known as immune dysregulation, and the latest research1 suggests a relationship between the benefits brought about by a diverse microbiome and effective immune health.
The “gut-brain axis,” as it is known, refers to the direct and indirect interaction between the gut microbiota in the digestive tract and the brain, which in turn affects the cellular components of the central nervous system2. In essence, this suggests that maintaining a healthy functioning gut microbiome can allow the body to react with agility that it otherwise could not, which naturally extends to how the body deals with pathogens and antigens. The key to ensuring that the gut is effectively playing its role in overall health—including immune system modulation—is to be aware of how we’re fueling it. What we put into our bodies has an effect on how it operates in a given capacity, and like many of our natural processes, what we consume ultimately alters how the body functions and reacts.
The Emerging Role of Fiber
Think of dietary fiber, and the first thoughts that spring to mind may be its ability to relieve constipation in the digestive tract and keep the system moving. But fiber’s benefits don’t end there. Sometimes referred to as “roughage” or “bulk,” dietary fiber is a food component that the body cannot easily digest or absorb and is found naturally in a wide spectrum of everyday foods. Notably, fiber is the preferred substrate, or “fuel,” for the good gut bacteria, stimulating its growth and activity.
A study3 conducted on behalf of Public Health England that found only 9% of adults aged 16-64 and 7% of adults over 65 in the United Kingdom obtain the recommended intake of 30 g of fiber per day. This means there is a great opportunity for the general public to boost their intake and take advantage of the many benefits of fiber.
Grain, rice, and other starchy foods, as well as fruits, vegetables, nuts, and seeds, are all noted as reliable natural sources of fiber. Significantly for consumers, high-fiber supplements are being brought to market that help to bridge the fiber gap and make the recommended daily intake simpler to achieve.
With 70% of the overall immune system being found in the gut, a mounting body of evidence points to the role of dietary fiber in supporting overall immune function. Research is ongoing, but studies suggest that fiber supports the gut’s own immune system function, which may bolster the wider body’s systems of protection.
Vitamins and Minerals
The nutrients that we put into our bodies can be an effective way to modulate our immune response and help strengthen the natural defenses. For the body to protect itself, it requires a suite of nutrients. What’s more, to get the full benefits from these nutrients, it’s essential that long-term gut health is supported, allowing the complex system of organs to function at their most effective.
As part of a long-term balanced diet, vitamins C, D, and A can play useful roles in bolstering immune function:
• Vitamin C supports the cellular function of both the innate and adaptive immune system4. It can also help by strengthening the epithelial barrier, the initial line of defense of the skin biome.
• Vitamin D has its own role to play, as immunologic cells can synthesize the active vitamin D metabolite, ostensibly allowing it to support the autocrine behavior of the cell milieu. Modern studies have revealed increased occurrence of several important immune disorders, including IBD, asthma, and allergies, particularly across “Westernized” societies.
• Vitamin A has been the subject of numerous recent studies with regards to strengthening the immune system. Research suggests that one way that the gut microbiota can regulate immune responses by adjusting a protein, retinol dehydrogenase 7, that activates vitamin A through the gastrointestinal tract5 and transforms it into the active form, retinoic acid.
There are several additional nutrients that are suggested to help improve the immune system’s functionality, including selenium, found in nuts and shellfish; omega-3 fatty acids; and zinc, found in rich quantities in meat and dairy products.
Studies are uncovering the full extent to which the trillions of bacteria in the gut microbiome strengthen and support immune response over a sustained period of time, outside the direct short-term effect of nutrients. The connection is demonstrable, but the precise mechanisms of action that cause this effect are still a topic of much debate across the medical, pharmaceutical, and food and supplements industries around the world.
The Human Microbiome Project, which maps and catalogues the microbiome communities in people with different diseases and conditions, could point towards the future of immune system conditions and unlock a deeper understanding of the interdependent relationships between the gut and the immune system.
The truly exciting part of this work is that when we come to understand collectively how bodily health and pathogens affect the makeup of the gut microbiome, we may be able to modulate the gut microbiome for the reverse effect; to impact our ability to respond to disease.
When looking to strengthen and support the immune system, it’s clear the gut could be our single most important tool—and perhaps one of the most unexpected.
Melanie Bulger is head of nutrition and regulatory affairs at Clasado Biosciences (United Kingdom).
1. Round JL et al. “The gut microbiome shapes intestinal immune responses during health and disease.” Nature Reviews. Immunology, vol. 9, no. 5 (May 2009): 313-323. Accessed at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4095778/
2. Ma Q et al. “Impact of microbiota on central nervous system and neurological diseases: the gut-brain axis.” Journal of Neuroinflammation. Published online March 1, 2019. Accessed at: https://jneuroinflammation.biomedcentral.com/articles/10.1186/s12974-019-1434-3
3. Public Health of England. Food Standards Agency. “National Diet and Nutrition Survey: Results from Years 7 and 8 (Combined) of the Rolling Programme (2014/2015 to 2015/2016).” Accessed at: https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/699241/NDNS_results_years_7_and_8.pdf
4. Carr AC et al. “Vitamin C and immune function.” Nutrients, vol. 9, no. 11 (2017). Accessed at: https://www.mdpi.com/2072-6643/9/11/1211/htm
5. Sandoiu A. “Immune system vs. gut bacteria: How vitamin A ‘keeps the peace’”. Medical News Today. Published January 3, 2019. Accessed at: https://www.medicalnewstoday.com/articles/324066#Vitamin-A-keeps-immune-response-in-check