Frequently referred to as the sunshine vitamin because of the way that sunlight exposure on the skin is a stimulant for its synthesis in the body, vitamin D is one of the most versatile nutrients for human health. In addition to its classic role in supporting calcium metabolism and promoting strong bones, research on vitamin D in the last decade or so has exploded to where this vitamin is now known to play significant roles in heart health, brain function, metabolic health, blood sugar regulation, blood pressure maintenance and so much more. This, of course, is in addition to its well-known potential in strengthening the immune system and fighting off attacks from viruses, bacteria and other insults. As it turns out, nearly all immune cells express vitamin D on their surface, which explains its indispensable role in ensuring immune vigilance. However, recent research has highlighted the interesting way in which this vitamin has its influential effects on immune regulation.

As it is known that the digestive tract is the primary immune organ in the body, housing between 70-80% of the immune system, research is revealing that vitamin D plays a significant role in regulating intestinal balance, or homeostasis, through interacting with the gut flora. It does this in several ways:

• Improves gut barrier integrity: Vitamin D confers protection to the gut barrier on several levels. It plays an indirect role in enhancing the mucus layer that coats the walls of the intestines and acts as an obstacle to exclude harmful bacteria from localizing into circulation. Going even further, vitamin D plays an important role in supporting the integrity of the epithelial lining of the intestines, including through reducing inflammation that can negatively impact or injure the cells lining the intestines, leading to healing of the intestinal cells. Vitamin D also increases the integrity of tight junctions between cells. Tight junctions are responsible for holding intestinal epithelial cells tightly next to each other, preventing dietary and bacterial toxins from entering circulation. A permeable gut barrier, or leaky gut, is associated with several chronic diseases. By supporting tight junctions, vitamin D enhances the functionality of the gut barrier, which is a key immune barrier.

• Interacts with the gut microbiome: An intriguing area of current research involves assessing the extent to which vitamin D plays a role in favorably influencing the diversity and makeup of the microbiome. While bacteria do not express vitamin D receptors on the surfaces of their cells, there is evidence that vitamin D supplements may indirectly influence gut bacterial composition.

• Enhances innate and adaptive immunity: Vitamin D has direct effects on both arms of the immune system. The innate immune system is the first line of defense and is put into motion quickly at the first sign of an immune insult; the adaptive immune system then becomes primed and provides a more targeted approach. Vitamin D enhances aspects of the innate immune system including the production and secretion of antimicrobial proteins such as cathelicidins from the intestinal epithelial layer, while also modulating and directing the functions of T cells and other immune cells that are components of the adaptive immune system.

Because of its broad role in affecting the immune system through the digestive tract and its influence on the microbiome, vitamin D is a foundational nutrient for immune protection and enhanced vigilance. Since surveys indicate that an estimated 60% of adults worldwide are suffer from vitamin D deficiency, supplementing with this vitamin becomes imperative to boost immune health and health overall.

References

• Fakhoury HMA et al. 2020. Vitamin D and intestinal homoeostasis: barrier, microbiota and immune modulation.
• Holick MF. 2017. The vitamin D deficiency pandemic: Approaches for diagnosis, treatment and prevention.

Tags: Vitamin D, vitamin D3, immune, microbiome, inflammation, digestive health, leaky gut