Vitamin D and Immune System

Lots of research exist that show vitamin D, specifically calcitriol, plays an important role in supporting the body’s immune system. The vast majority of the research that have been performed used cultured cells, which means that cells were taken out of a body and were then grown in special nutrient solutions. Animal testing has also been conducted, in which certain animals had severe vitamin D deficiency. Some animals were used that had their genes altered so that they no longer had active proteins to control vitamin D action or vitamin D metabolism.

Why Studies Matter

While animal testing is controversial and laboratory testing is not always accepted as truth, when the results of both are put together, you get what is called ‘proof of principle’. The proof of principle in these tests was that vitamin D is vital to the support of the immune system. They also weren’t the only studies on the subject. Some looked specifically at whether there is a link between UV exposure (which varies depending on geographical latitude and season), levels of serum 25-hydoxitamin D (vitamin D) and various medical conditions and infections.

Put together, the results of all these studies can safely conclude that calcitriol (vitamin D) is vital to building a strong immune system. What they are still struggling with, however, is determining what the adequate levels are to make sure enough calcitriol is present in the body in order to properly support the immune system. Research in this field continues.

Vitamin D and the Immune System – What Is Known

It is known that the body contains B cells and T cells, and that some of these cells can respond to calcitriol because they have vitamin D receptors. Other cells have phagocytes, which can convert vitamin D in its pure form (25-hydroxyvitamin D) into calcitriol. The suggestion that can be made from this is that phagocytes and T and B cells can communicate and that they use calcitriol to do that.

Various studies on the immune system’s cells have demonstrated that the presence of calcitriol means that the adaptive immune system’s features are blocked. With this, people would develop autoimmune disorders. In animal studies, it has been demonstrated that the absence of calcitriol leads to an increased chance of autoimmunity, whereby the healthy cells of the body are attacked by the immune system.

Autoimmunity, however, is not primarily caused by a vitamin D deficiency. Rather, if levels of vitamin D are low, the immune system cannot function properly. The problem is that there are still no clear guidelines on how much vitamin D an individual should have in order to properly support the immune system. This is because there are too many variables, including geographical location, time spent outdoors, age, weight, gender and ethnicity, to name but a few.

How Vitamin D Influences the Immune System

Researchers know that there are two primary ways in which vitamin D, particularly calcitriol, can influence the immune system:

1. During autoimmunity, T cells are not armed and triggered if calcitriol is present. T cells are some of the most important cells in autoimmunity. Their role is significantly diminished if calcitriol is present, as it blocks the production of certain specific helpers required by T cells in order to produce autoimmunity. When the production of these cells is blocked, it is less likely that a T cell will confuse a native cell for a foreign one. This, in turn, means that fewer T cells, known as the ‘killer cells’ are produced as well. In layman’s terms: when there is sufficient vitamin D, there is sufficient calcitriol and when there is sufficient calcitriol, the T cells won’t attack the body’s normal tissues.

2. Calcitriol has also been shown to block certain chemicals that generally attack and kill native tissue. Those are the B cells, which are equally responsible for spotting and removing foreign tissues as what the T cells are. However, the B cells produce the actual chemicals that are needed to destroy tissue. Calcitriol stops these cells from producing this chemical, as it lowers the antibody response. For instance, when the beta cells that are found in the pancreas have diminished destruction, people with type 1 diabetes will experience fewer symptoms, so long as their levels of calcitriol and vitamin D are right.

How to Boost Your Immune System Using Vitamin D

There are a number of different ways in which you can boost your levels of vitamin D. The most important things to consider are:

1. Make sure that you check what your vitamin D level. This is often a regular part of a routine blood test, but do ask your physician whether or not a count is included.
2. Discuss supplementation with your physician after your blood test. The current national recommended daily value is 600 IU, but some people may need more, if their physicians decide this.
3. Weather permitting, and particularly in warmer climates, try to go outside more regularly. Exposing your hands and face to the sun for about 20 to 30 minutes a day, four times a week is enough to get your vitamin D level back to what it should be naturally.
4. Check your diet. Various foods have been fortified with vitamin D, including milk and cereal. Other foods, including oily fish, contain natural levels of vitamin D. Do make sure that you actually check the label to see whether or not it is fortified. Do also make sure that you use organic sources. If not, the chemicals, pesticides and genetic modifications in the product may completely cancel out the benefits of the vitamin D.

Resources and References:

Vitamin D and the Immune System – Effects of vitamin D on immune system. (
Vitamin D and Influenza – Relationship between vitamin D and influenza. (Vitamin D Council)
Why Vitamin D Is Better than Any Vaccine and Improves Your Immune System by 3-5 Times – How vitamin D improves immune system. (
Vitamin D Status, 1,25-dihydroxyvitamin D3, and the Immune System – Relationship between vitamin D level and immune system. (American Journal of Clinical Nutrition)
How to Boost Your Immune System – Boosting the immune system. (Harvard Health Publications)
Vitamin D Controls T Cell Antigen Receptor Signaling and Activation of Human T Cells – Vitamin D and human T cells. (Nature Immunology)
Vitamin D for Treatment and Prevention of Infectious Diseases – Review of randomized controlled trials on using vitamin D for treating infectious diseases. (