Vitamin D prevents influenza and respiratory infections

Vitamin D prevents influenza and respiratory infectionsIt is hardly a coincidence that so many of us contract virus infections in the course of the winter. It is because we lack vitamin D, which we are unable to synthesize when the sun sits too low in the sky. Danish scientists have discovered how vitamin D activates the immune system, and a comprehensive meta-analysis shows how vitamin D supplements can prevent colds, flus, and related complications.

Vitamin D can even counteract inflammatory conditions such as bronchitis and aching joints that affect many people during the winter period. The question is, how much do we need?

Our diets only provide minimal amounts of vitamin D, and regular multivitamin supplements are not likely to deliver the amounts of vitamin D that are needed for optimal immune functioning. Too much time spent indoors, ageing processes, having dark skin, overusing sunscreen, being overweight, having type 2-diabetes and kidney diseases, and overconsuming calcium and cholesterol-lowering medicine can all increase our risk of lacking vitamin D all year round.
A vitamin D deficiency goes unnoticed in the beginning, yet it affects the “storm troops” of our immune system, leaving us increasingly vulnerable to virus infections and other complications such as bronchitis, and infected sinuses, ears, and lungs.

The non-specific (or innate) immune system is comparable to storm troops consisting of various proteins and a major part of our white blood cells. It combats most types of pathogens without us even knowing about it. Our specific (or adaptive) immune defense comprises of T and B cells plus antibodies that are like special troops that come to our rescue in situations where our non-specific immune system comes up short. Afterwards, the body develops a type of immunity towards the threat.

Vitamin D is determining for the activation of our immune defense

Vitamin D activates both the non-specific and the specific immune defense. Our respiratory tract harbors particularly many white blood cells called macrophages that depend on vitamin D in order to be able to attack pathogens. Vitamin D also boosts certain antibiotic peptides in our lungs.
Danish researchers have discovered how different T cells depend entirely on vitamin D. According to Carsten Geisler from the Faculty of Health and Medical Sciences at the University of Copenhagen, vitamin D helps activate the initial stage of the T cells’ attack, which is crucial.
Once T cells are exposed to virus and bacteria, they launch an immediate chemical reaction and deploy signals or “antennae” (more accurately called vitamin D receptors – or VDR) that T cells use to locate vitamin D in the bloodstream. T cells depend on extra vitamin D to help them divide and form an entire T cell army that can direct a very effective attack of the enemy.

When specific T cells are to attack a virus or a cancer cell, they take on one of several forms:

T helper cells are like officers that send out signaling substances telling what to attack. They also instruct B cells to produce antibodies.

T killer cells obey the command and destroy virus-infected cells and cancer cells using cytotoxic substances.

Regulatory T cells help pull the brake on T killer cells, once the enemy is defeated. That way, unnecessary tissue damage is avoided.

Memory T cells serve to remember (recognize) microorganisms by identifying specific characteristics (antigens) and mobilizing some sort of immunity.

Vitamin D needs to get all the way into the T killer cells

The scientists from the Faculty of Health and Medical Sciences made their groundbreaking discovery by isolating T cells from human blood in the laboratory. They found that T cells, which had never been in action, required vitamin D in order to get started. Once vitamin D has attached to a receptor in the T killer cells, the vitamin is carried way into the nucleus that is then instructed to produce a protein called PLC-gl (5,6). This is the protein that T killer cells need so they can divide into an entire army that can kill off intruding microorganisms and cancer cells. However, if T cells are not able to absorb enough vitamin D from the blood, they are unable to collaborate, attack, or develop immunity.
The groundbreaking Danish study is published in the science journal Nature, and the discovery sheds a whole new light on the general lack of vitamin D, which is something that needs to be addressed.


You will probably not notice if you are running low on vitamin D. However, you can be sure that your immune defense will.

A vitamin D deficiency increases the risk of TB and many other infections

Before the discovery of antibiotics, doctors gave tuberculosis patients vitamin D therapy by placing them outdoors in the sun or by giving them cod liver oil. However, science did not know anything about the underlying mechanisms.
Meanwhile, a number of studies have shown that low levels of vitamin D are linked to an increased risk of infections. A study of 19,000 people carried out during the period from 1988-1994 demonstrated that those with low vitamin D levels in their blood were more likely to get respiratory infections, even when the scientists adjusted for confounding factors such as the time of year, age, genes, BMI, and race.
Another study (of 800 Finnish soldiers) showed that those who had the lowest levels of vitamin D in their blood had more sick days due to respiratory infections compared with those who had the highest vitamin D levels.

Vitamin D supplements reduce influenza by 42-50 per cent

The use of vitamin D supplements as a means of prevention of influenza and other infections has produced contradictory results and caused confusion. Nonetheless, a meta-analysis conducted by scientists at the Queen Mary University of London has clarified matters. It turns out that those who have the lowest levels of vitamin D in their blood to begin with, benefit the most from taking a vitamin D supplement.
According to Professor Adrian Martineau, who headed the research, the greatest effect is seen with daily use of vitamin D. Vitamin D supplements have the potential to reduce the risk of acute respiratory infections by 50% in those who already have low levels of vitamin D.
The meta-analysis is published The BMJ, one of the world’s leading journals. It reveals how effective vitamin D supplements are, even when compared to vaccines. In fact, vaccines are only able to address one single type of influenza, whereas vitamin D strengthens the immune response against all microbes.
A double-blind, placebo-controlled study published in the American Journal of Clinical Nutrition in 2010 showed that school children had a 42% lower flu rate when they took supplements of vitamin D.

A blood sample can determine your vitamin D status

Blood levels of vitamin D are measured as 25-hydroxyvitamin. The official lower threshold value is 50 ng/ml, but many scientists believe this is insufficient and recommend as much as 75-100 ng/ml for optimal disease prevention.

Vitamin D also protects against inflammatory conditions like bronchitis, asthma, and aching joints

Vitamin D protects against bronchitis and asthma by means of two mechanisms: It strengthens the immune system, and it counteracts inflammation.
It is necessary for the body to be able to fight an infection. However, the immune system must not react too violently. If it does, we risk chronic conditions and tissue damage. Therefore, vitamin D is vital for preventing bronchitis, asthma, aching joints, and many other conditions that involve inflammatory response.
A study that is published in Nutrients in 2015 shows that vitamin D is both directly and indirectly involved in regulating T cells and their production of various signaling substances such as interferon and interleukin.

How much vitamin D do we need?

The reference intake (RI) for vitamin D varies slightly, depending on the country. However, health authorities generally recommend vitamin D supplements to children aged 0-2 years, pregnant women, children and adults with dark skin, people who do not spend time outdoors or are veiled, and residents at senior homes or people older than 70 years. New studies have shown that overweight individuals and diabetics also have an increased need for vitamin D.
Many researchers claim that the actual need for vitamin D is way above the reference intake level and suggest daily intake levels in the range of 30-100 micrograms. It is easy to synthesize this amount of vitamin D on a hot summer day, but during the winter we need supplements, as even a healthy and balanced diet only contributes with minimal amounts of the nutrient.

An overview of the immune system

Defense Non-specific (innate) Specific (adaptive)
Functions as Storm troops, messengers and trash collector.
Special troops that develop immunity.
Mature after birth.
Mechanical and biological Skin and mucosa.
Specific compounds in the ”acute” phase Interferon
Complementary system
Direct cellular destruction Dendritic cells
NK cells
T cells. Primarily responsible for virus, fungi, and abnormal cells.
B cells and antibodies. Primarily responsible for bacteria and toxins.



Echinacea, garlic, and other herbs may also strengthen the immune system, but they can never replace vitamin D. Our primary source of this nutrient is the sun (during the spring and summer season).


Martineau Adrian et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. The BMJ 2017

University of Copenhagen. Vitamin D crucial to activating immune Defences. 2010

Margherita T. Cantona et al. Vitamin D and 1,25 (OH)2D Regulation of T-cells. Nutrients 2015

Urashima M, et al. Randomized trial of Vitamin D supplementation to prevent seasonal influenza A in school children. Am J Clin Nutr 2010

University of Colorado Anschultz Medical Campus. Vitamin D reduces respiratory infections. ScienceDaily November 2016

Cynthia Aranow. Vitamin D and the Immune system. J Investig Med. 2011

Pernille Lund. Immunforsvarets nye ABC. Hovedland. 2012