Vitamin D and How it Supports a Healthy Gut Microbiome

Vitamin D and How it Supports a Healthy Gut Microbiome

Toral Shah, nutritional scientist, functional medicine practitioner and founder of The Urban Kitchen is here to talk to us about the relationship between Vitamin D and the gut microbiome.


Our gut microbiome is essential for balancing day-to-day bodily functions. This is via both its metabolic activity (chemical processes) and impact on the immune system.


This system requires maintaining a delicate balance for optimal health and well-being. Any imbalance could have a profound impact on such things as our weight, health and overall quality of life. Imbalance or lack of biodiversity of the gut microbiome (which might be due to nutrition and lifestyle choices) could contribute to many diseases including risk of cancer, type 2 diabetes, irritable bowel syndrome, cardiovascular disease, allergies, mood disorders and inflammatory bowel disease.


In a similar way, a lack of vitamin D is also associated to an increasing range of diseases and ill health including poor musculoskeletal health, as well as immune and inflammatory diseases. Vitamin D deficiency is a growing problem, and is linked to many of the same diseases that are caused by imbalances in the gut microbiome.


Vitamin D is not just a vitamin, but in fact a steroid hormone which manages a huge proportion of our biological functions, including the regulation of calcium in our blood. It also modulates insulin secretion, synthesis and secretion of hormones, regulation of genes, and function within the immune system.


Vitamin D is normally synthesized in skin by exposure to the sun, where UV light generates pre-Vitamin D. This undergoes further reactions to make an active form of vitamin D, cholecalciferol or Vitamin D3. In the Northern hemisphere, (ie Northern Europe, Canada, Scandinavia and some of the USA), we don’t have enough UV light from the sun in winter (end of Oct to March) to make vitamin D and so are often deficient.


Research studies in both animals and humans have shown that vitamin D promotes intestinal health and can change the gut microbiome and the diversity of the bacteria. A Canadian study showed that exposure to sunlight or UVB light can modulate the gut microbiome – this was most effective in those that were vitamin D deficient. In early 2020, a study in teenage girls showed that supplementing with a high dose of vitamin D changed the composition of their gut microbiomes, increasing the proportion of beneficial bacteria.


There are several potential mechanisms by which vitamin D may affect the gut microbiome. One of these may be due to the effect on the immune system as vitamin D has anti-inflammatory effects. Vitamin D deficiency has been shown to promote an inflammatory environment which can create imbalance in the gut microbiome.


Given that one of the most important roles of vitamin D is for our immune system to function optimally, getting sufficient vitamin D is key for long-term good health. So how can we do this? In the summer, we need to ensure we spend at least 15 – 20 minutes each day in the sun without sunscreen. In the winter, we need to supplement with vitamin D and eat vitamin D rich food such as oily fish and eggs. People of colour and older people require higher levels of vitamin D – much higher than Public Health England recommends as their recommendations are based on young white patients.


So, in summary, vitamin D plays a crucial role in the gut microbiome and gut bacteria diversity, as well as the immune system. We should all be careful therefore to ensure we get an adequate intake of vitamin D to help safeguard our health.





Leblanc et al – Bacteria as vitamin suppliers to their host: a gut microbiota perspective: Current Opinion in Biotechnology 2013; 24, 160 - 168

Layden et al – Short chain fatty acids and their receptors: new metabolic targets: Translational Research 2013; 161 – 131-140

Ivanov et Honda – Intestinal microbes as immune modulators: Cell Host and Microbe 2012;12 – 496 - 508

Rhee et al – Principles and clinical implications of the brain-gut-enteric microbiota axis: Nature Reviews Gastroenterology & Hepatology 2009; 6 – 306 – 314

Bosman et al - Skin Exposure to Narrow Band Ultraviolet (UVB) Light Modulates the Human Intestinal Microbiome Front. Microbiol., 24 October 2019

Tabataeizadeh et al - The effects of high doses of vitamin D on the composition of the gut microbiome of adolescent girls Clin Nutr ESPEN 2020 Feb;35:103-108.