Vitamin D: Its Role in Immunity and Gut Health
Vitamin D has been getting a lot of attention recently as a result of a study suggesting that it helps fight Covid-19 (more on this below). But it does a lot more than that! Vitamin D has many important roles to play in the body and its processes, which is why increasingly-common deficiencies of this valuable nutrient are troubling.
What is Vitamin D and what is its role in the body?
Vitamin D, a fat-soluble vitamin, is an important micronutrient that plays a critical role in various processes in the body. Despite its name, Vitamin D actually works more like a hormone than a vitamin, as it binds to multiple cell receptors all over the body, causing changes in how those cells function (whereas vitamins do not normally bind to cell receptors but rather assist in enzyme reactions).
Most of our organs and cells have Vitamin D receptors, so it’s logical that inadequate levels can have a negative effect on nearly every area of the body.
In fact, Vitamin D controls the expression of more than two hundred genes and the proteins regulated by those genes. It assists in calcium absorption, bone development, balancing mineral levels in the body, modulation of cell growth, immune system function, and the reduction of inflammation.
Most of our organs and cells have Vitamin D receptors, so it’s logical that inadequate levels can have a negative effect on nearly every area of the body.
Where do we get Vitamin D from?
We can get Vitamin D from certain foods and through direct supplementation, but we also have the ability to make it.
The reason Vitamin D is often referred to as “the sunshine vitamin” is because our skin actually makes Vitamin D3 when it’s exposed to ultraviolet light from the sun (UVB light). In fact, UVB rays trigger a reaction whereby our body converts a type of cholesterol into Vitamin D3, which is then stored in the skin, slowly released into the blood and then converted into a hormone-like chemical (called calcifediol) in the liver and kidneys.
The best dietary sources of Vitamin D3 are oily fish, organ meats and eggs.
This metabolisation takes place regardless of whether the Vitamin D3 has been made by our skin, taken as a supplement, or extracted from our food, converting it to calcifediol.
The best dietary sources of Vitamin D3 are oily fish (sardines, cod liver oil etc), organ meats (such as liver) and eggs (particularly yolks).
What’s the difference between Vitamin D and D3?
Vitamin D3 (cholecalciferol) is one of the forms of Vitamin D, along with D2. Both D2 and D3 need to be converted by the liver and then by the kidneys into the main form of vitamin D that circulates in your body: calcifediol (also called calcidiol). But D3 appears to raise levels of active Vitamin D more effectively than D2, so is by and large the go-to option for Vitamin D supplements.
Vitamin D and the Immune System
Vitamin D is vital for regulating several key components of the immune system. It binds to the first line of our immune cells and keeps them less reactive to self-antigens, making them less likely to attack the body’s own tissues (which is precisely what happens in the case of an autoimmune disease).
In this way, Vitamin D acts as an immunomodulator, helping to regulate inflammation, while supporting the immune system’s T-cells and B-cells, both of which play a key infection-fighting role.
Vitamin D acts as an immunomodulator, helping to regulate inflammation
Vitamin D therefore helps decrease inflammation and may be critical in controlling autoimmune and inflammatory diseases, and as it helps control cell growth, it is also essential for healing.
It should be noted that Vitamin A is necessary for effective absorption of Vitamin D, and it too helps regulate and support healthy development of immune cells.
A note on Vitamin D and Covid-19
The study that has been in the spotlight recently was a pilot trial, which means a small sample size, but it was nevertheless a randomized controlled clinical trial, which makes it a valuable piece of research.
The study used oral calcifediol, rather than standard Vitamin D supplementation. As mentioned above, calcifediol is the main metabolite of Vitamin D3, which means it is what Vitamin D3 turns into once it is metabolised by the body.
In summary, the study found that the risk of ICU admission was reduced by 93% in Covid-19 patients taking oral calcifediol. More specifically, the control group (those not taking calcifediol) had a 50% rate of ICU admission and 2 deaths, while the calcifediol group had just a 2% rate of ICU admission, and no deaths.
This study was the first attempt to use Vitamin D to treat Covid-19. The results seem to be in line with previous findings that having low Vitamin D3 levels increases the risk of Covid-19 diagnosis and of more severe symptoms.
Vitamin D and Gut Health
There are several ways in which Vitamin D is important for gut health, and IBD in particular.
To begin with, Vitamin D has been shown to be essential for maintaining the integrity of the gut wall, which is crucial when it comes to IBD. It is also of vital importance when dealing with intestinal permeability, also known as ‘leaky gut syndrome’ (usually present in those suffering with autoimmunity), and in healing the gut overall.
Vitamin D has been shown to be essential for maintaining the integrity of the gut wall.
It has also been shown that exposure to sunlight/UVB light can actually alter the human gut microbiome (particularly in people with a Vitamin D deficiency) and significantly increase gut microbial diversity. This study also confirmed that:
“Vitamin D deficiency has been shown to promote an inflammatory environment which leads to dysbiosis of the gut microbiota, even in clinically healthy individuals. Oral vitamin D supplementation is known to be beneficial for individuals who suffer from chronic inflammatory diseases.”
As an immunomodulator, and with its ability to reduce both inflammation and auto-immune responses, Vitamin D plays an important role in managing IBD. Indeed, according to this study, Vitamin D deficiency has been linked to an increased risk of autoimmune diseases, and in the development and severity of IBD in particular. Epidemiological studies even suggest higher rates of both IBD and rheumatoid arthritis in countries further away from the equator (and therefore with less Vitamin D-creating sunlight).
The immunoregulating properties of Vitamin D play a significant role in the expression and severity of IBD.
Another study noted that 38.1% of Crohn’s patients and 31.6% of ulcerative colitis patients have a Vitamin D deficiency, and the immunoregulating properties of the vitamin play a significant role in the expression and severity of IBD by affecting the gut microbiome and the body’s inflammatory response.
All these findings make a strong argument for using Vitamin D to support and enhance gut health in general, and for managing IBD in particular.
Vitamin D and Bone Health
Vitamin D is probably best known for being vital for strong and healthy bones and teeth. Without it our bodies can’t absorb more than 10 to 15 percent of the calcium from our food. This is because Vitamin D regulates the absorption and transportation of calcium (as well as phosphorus and magnesium) in the body, ensuring it gets distributed to our tissues effectively.
Without Vitamin D our bodies can’t absorb more than 10 to 15 percent of the calcium from our food.
If there are insufficient levels of Vitamin D, instead of calcium being incorporated into tissues, it gets excreted by the body. This then means that there is not enough calcium in our cells and blood so, to remedy this, calcium is drawn out from our bones to compensate, thus weakening them, and increasing the risk of osteoporosis and bone fractures.
Vitamin D and Mental Health
Vitamin D also has a role to play in mental health, and low levels have even been associated with increased anxiety and depression.
Vitamin D activates genes that regulate and release neurotransmitters, such as dopamine and serotonin (our ‘happy hormones’), that affect brain function and development. For example, getting adequate amounts of Vitamin D helps maintain our body’s natural production of serotonin because Vitamin D activates the gene that converts tryptophan (an essential amino acid) into serotonin. At night, our brain converts serotonin into melatonin (the ‘sleep hormone’), which is essential for good quality sleep, which in turn affects our mental health (as well as our physical wellbeing). It’s truly a cyclical domino-effect situation!
Furthermore, serotonin is important for regulating digestion, so this is one more way in which Vitamin D impacts the gut.
Vitamin D Supplementation
The recommended daily dose (RDA) of Vitamin D is around 400 IU. However, there seems to be a general consensus that this will not meet most people’s needs. As such, a daily dose of 2000 IU is considered more appropriate (though some recommend even higher doses).
Vitamin D blood levels should be monitored, both to ensure that there is no deficiency, but also to ensure that levels are not too high, as this can result in Vitamin D toxicity. It’s best to discuss this with your doctor, who can advise and monitor you accordingly.
Conclusion
Vitamin D plays many important roles in the body, and can be valuable when it comes to managing inflammation and supporting the body as a whole. So it’s definitely worth getting your levels checked and discussing possible supplementation with your doctor, especially if you have an autoimmune disease like IBD.