According to the Center for Disease Control, vitamin D is consumed by approximately 69% of adults monthly. It is widely consumed in our diet, but it can be synthesized by our own body (Mishra et al., 2023). This prohormone is one of the most discussed in daily life due to its known benefits and importance for bone maturation and development. However, another approach can be considered when talking about vitamin D and its association to gut health. The gut microbiota is composed by organisms such as bacteria that exist in harmony with the stomach and assist in food digestion. Vitamin D can support the health of this microbial community.

Vitamin D

Vitamin D is a fat-soluble hormone that can be consumed by diet, through fish oil, meat, egg yolks, and other dietary foods (National Health Service, 2020). It can also be synthesized by our skin due to UV light exposure, which triggers vitamin D synthesis (National Health Service, 2020). Absorption from the diet is made through the small intestine, both by passive diffusion and by a membrane carrier. Passive diffusion is a process in which a molecule or hormone is absorbed passively by the cell’s membrane, in contrast to a membrane carrier in which the absorption is assisted by a protein in the membrane. 

As mentioned before, this vitamin is fat soluble, that means that for better absorption it requires dietary fat (DynaMed, 2025).  This can be affected by intestinal malabsorption conditions such as celiac disease and pancreatitis in which there’s a decreased ability to absorb nutrients (DynaMed, 2025). The process of synthesis in the body requires both liver and kidneys for hydroxylation, to go from an inactive form to an active form (NIH: Office of Dietary Supplements, 2020). This is why liver and kidney problems may affect vitamin D synthesis (DynaMed, 2025; NIH: Office of Dietary Supplements, 2020).

 Vitamin D plays a big role in our bodies such as bone metabolism, anti-inflammation, cell proliferation, differentiation, myocardial contractility and insulin production (DynaMed, 2025). It is necessary for calcium reabsorption in the gut and phosphorus homeostasis, which allows for bone mineralization and metabolic function(DynaMed, 2025). Deficiency can lead to osteomalacia in adults and rickettsia in children, these are conditions related to bone weakness where they could break more easily(DynaMed, 2025; NIH: Office of Dietary Supplements, 2020). Other conditions that could be associated with deficiency of this vitamin are autoimmune conditions such as diabetes, inflammatory bowel disease and colorectal cancer(DynaMed, 2025).

Gut Microbiome

Symbiotic relationship of bacteria with our body is essential for development and function of various organs, however, this is no exception with our gut microbiome (Singh et al., 2020). The gut microbiome is composed of bacteria, fungi, archaea, and viruses that coexist with the gut. These organisms are crucial for regulation of gut health (Anto & Blesso, 2022).  In addition, each microbiome is unique to each person, adding complexity to the stomach and intestine ecosystem (Anto & Blesso, 2022). 

The microbiome maintains the integrity of the gut lining (layer of cells inside the gastrointestinal system), helps with host immunity, digestion and metabolism of a person’s diet (Anto & Blesso, 2022). Aids in metabolism of sugars and vitamins, such as vitamin K, vitamin B1, B9 and B12. It can even suppress the growth of invasive bacteria and pathogens that may alter the microbiome (Akimbekov et al., 2020). Disturbance to the microbiota due to chemicals, diet, infections and inflammation response has been associated with various conditions. For example, diabetes, intestinal bowel disease, and cancer; reinforcing how vital it is for immunity and metabolism of the gastrointestinal (GI) system (de Vos et al., 2022). 

Vitamin D and Benefits in Gut Microbiome

There has been a correlation with the effects of vitamin D with the gut microbiome.  Vitamin D helps regulate the gut’s mucosa by maintaining and healing the lining.  There is a receptor called Vitamin D receptor (VDR), once Vitamin D is consumed and detected in our body the receptor attaches to the vitamin, creating a VDR-Vitamin D complex (MedlinePlus, 2020). This complex promotes the transcription of proteins. In terms of the gut microbiome, this VDR-Vitamin D complex increases the expression of various intracellular junction proteins (Akimbekov et al., 2020). These junction proteins promote a stronger mucosal lining of the GI system. 

This receptor (VDR) with the presence of Vitamin D , can also stimulate an anti-inflammatory response and the expression of AMPs (antimicrobial peptides) (Akimbekov et al., 2020). AMPs are smaller proteins that boost the immune system and play a role in inhibition of pathogens that can be detrimental for the gut (Akimbekov et al., 2020). The microbiota also responds to the presence of Vitamin D by promoting more creation of the Vitamin D receptor, allowing more complexes to roam in our gut (Aggeletopoulou et al., 2023). Lastly, some research studies have presented the possibility of vitamin D changing the microbiota to allow growth of more beneficial bacteria that can help us in our metabolism (Tangestani et al., 2021).

​Deficiency of vitamin D may be related to a reduced reinforcement and protection of intestinal lining, therefore no benefits would be obtained. It can reflect decreased antimicrobial protection and a decreased anti-inflammatory response (Akimbekov et al., 2020). Deficiency of the vitamin in contrast could increase risks for GI conditions such as IBD (Inflammatory Bowel disease) and cancer (Aggeletopoulou et al., 2023).  There’s a lack of research on the long term effects of inadequate levels of vitamin D in the gut microbiome, nonetheless research reviews on the benefits in association with vitamin D in stomach and intestine health. 

Conclusion

Vitamin D has known benefits with bone development, but it extends its benefits within the stomach and intestine. Associations can be made due to research on how vitamin D regulates and protects the GI system. Vitamin D not only supports the gut microbiome but also strengthens the integrity of the gastrointestinal system at the cellular level. This could be a point of consideration for further research where Vitamin D can be scoped as supportive treatment for patients with diagnosed Inflammatory Bowel Diseases such as Crohn’s, Ulcerative colitis or even cancer. It could also be used as a preventative measure in decreasing diagnosis. However more research is needed to truly understand and correlate at what levels or dosage of vitamin D is required to reap its benefits. ​

In the meanwhile, it is recommended to have a good balanced diet, as well as moderate sun exposure (10 to 15 minutes) and maintain adequate levels of vitamin D. According to NIH, adults should consume 15 micrograms (mcg) or 600 international units (IU) per day. Ultimately, future research may determine if Vitamin D could play a role in preventative care for gastrointestinal diseases.

References

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2. NHS . (2020) Vitamin D. Available from: https://www.nhs.uk/conditions/vitamins‐and‐minerals/vitamin‐d/ 
3. DynaMed. Vitamins for Disease Prevention. EBSCO Information Services. Accessed March 31, 2025. https://www.dynamed.com/prevention/vitamins-for-disease-prevention
4. NIH: Office of Dietary Supplements. (2020). Vitamin, D. Health Professional Fact Sheet Available online: https://ods.od.nih.gov/factsheets.VitaminDHealthProfessional/ 
5. Singh, P., Rawat, A., Alwakeel, M. et al. The potential role of vitamin D supplementation as a gut microbiota modifier in healthy individuals. Sci Rep 10, 21641 (2020). https://doi.org/10.1038/s41598-020-77806-4
6. Anto, L., & Blesso, C. N. (2022). Interplay between diet, the gut microbiome, and atherosclerosis: Role of dysbiosis and microbial metabolites on inflammation and disordered lipid metabolism. The Journal of Nutritional Biochemistry, 105, 108991. 
7. Akimbekov, N. S., Digel, I., Sherelkhan, D. K., Lutfor, A. B., & Razzaque, M. S. (2020). Vitamin D and the Host-Gut Microbiome: A Brief Overview. Acta histochemica et cytochemica, 53(3), 33–42. https://doi.org/10.1267/ahc.20011 
8. de Vos, W. M., Tilg, H., Van Hul, M., & Cani, P. D. (2022). Gut microbiome and health: mechanistic insights. Gut, 71(5), 1020–1032. https://doi.org/10.1136/gutjnl-2021-326789 
9. MedlinePlus [Internet]. Bethesda (MD): National Library of Medicine (US); [updated 2020 Jun 24]. VDR gene, Vitamin D receptor. https://medlineplus.gov/genetics/gene/vdr/ 
10. Aggeletopoulou, Ioanna et al. (2023). Vitamin D and Microbiome The American Journal of Pathology, Volume 193, Issue 6, 656 – 668
11. Tangestani, H., Boroujeni, H. K., Djafarian, K., Emamat, H., & Shab-Bidar, S. (2021). Vitamin D and The Gut Microbiota: a Narrative Literature Review. Clinical nutrition research, 10(3), 181–191. https://doi.org/10.7762/cnr.2021.10.3.181