Vitamin D – Our Weapon Against the Flu!
Holistic Living

Vitamin D – Our Weapon Against the Flu!


19 June 2015


Vitamin D plays a crucial role in our immune system to fight infections. Ironically, even though our bodies can produce its own vitamin D from sunlight and we just so happen to live in the tropics, most of us have a deficiency. How is this possible?

We avoid the sun like the plague, then we seek shelter in cars, houses, malls and offices. We take early morning walks before the sun comes out or evening walks when the sun has already set. If we do, on the rare occasion, expose ourselves to the sun during the day, we slather on layer upon layer of sunscreen. Some people even take it a step further using umbrellas to shield themselves from the heat. Given these behaviours, it’s no surprise that vitamin D deficiencies are endemic.

What is vitamin D

Vitamin D is actually a steroid hormone produced from cholesterol. When our skin is exposed to sunlight, ultraviolet B radiation is absorbed by a cholesterol-like molecule found in the skin. This creates previtamin D3. With help from the body’s heat, previtamin D3 is converted to vitamin D, which leaves the skin cells immediately to go into the bloodstream. In its current form, vitamin D is quite useless. It needs to go through a two-step conversion process to be activated.

First, the vitamin is converted into its storage form called calcidiol in the liver. Completed mostly in the kidneys, calcidiol is then converted to calcitriol which is the active, steroid hormone form of vitamin D. Calcitriol travels around the body and enters cells where it interacts with vitamin D receptors (VDR). When vitamin D interacts with these receptors, signals are sent to the cells directing them to take a particular action.

VDRs are present in almost every tissue type in the body. This indicates that our tissue, and consequently our bodies, need vitamin D to function adequately.

Vitamin D and Influenza (Flu)

Vitamin D is anti-inflammatory, antimicrobial and antiviral, decreasing the likelihood that the immune system will malfunction. It also reinforces the body’s natural defences against bad bacteria and inflammation.

1. Vitamin D can protect us against the flu

Numerous studies show that vitamin D reduces the risk of contracting the flu and the first connection was made in 1992 by a researcher named Robert Edgar Hope-Simpson. His studies suggest that the flu is seasonal because people receive less sunshine, and thus vitamin D, in winter.

Dr John Cannell’s experience further supports this. He had been giving his patients 2000 IU (international units) of vitamin D when a flu epidemic broke out. Despite interacting with people who were ill, none of his patients contracted the flu.

2. Vitamin D helps us fight infections

Vitamin D is critical for our innate immunity (our first line of defense). It works by increasing our body’s production of antimicrobial proteins (AMPs). These proteins are much more effective than synthetic antibiotics or antivirals at destroying invading germs and viruses.

For example, activated vitamin D tells macrophages (our immune system’s germ-killing cells) to create cathelicidin, one of the AMPs. Cathelicidin is a protein that specifically kills infective agents, thus protecting us against foreign invaders that we contract from our environment.

From 2008 to 2009, a study was conducted in Japan to evaluate the relationship between vitamin D and physician-diagnosed seasonal influenza. The results found that school children who were given 1200 IU of vitamin D3 every day had significantly fewer incidents of flu compared to the children who didn’t.

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3. Vitamin D can help reduce inflammation caused by the influenza virus

Cytokines are a part of our immune system which respond to bacterial and viral infections. To protect us, they create inflammation that makes the environment difficult for invaders to survive. Problems can arise when the immune system goes into overdrive as a cytokine storm can turn out to be more detrimental than helpful.

Viruses also work in sneaky ways, stimulating cytokines to make the surrounding cells become more porous and accessible to other viruses. As more and more inflammatory cells are released, more mucous-filled white blood cells and fluid fill the lungs. Vitamin D however can reduce the amount of inflammatory cytokines produced by the influenza virus to prevent these adverse effects.

4. High levels of vitamin D may help you recover from the flu faster

Some studies have shown a relationship between vitamin D levels and the duration of flu. A study conducted at the Greenwich Hospital in Connecticut showed that people who had levels of vitamin D higher than 38 ng/ml recovered from the flu within approximately 2 days. On the other hand, those with levels below 38 ng/ml recovered in an average of 9 days.

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Sources of Vitamin D

It is difficult to obtain sufficient amounts of vitamin D through diet alone. Aside from some mushrooms and fatty fish like salmon, very few foods contain decent levels of vitamin D. If you do need to eat something that is vitamin D-rich, cod liver oil is your go-to source as one tablespoon gives you 1360 IU.

Sunlight is still by far the best way to increase your vitamin D levels. According to Dr John Cannell, founder of the Vitamin D Council, just twenty minutes of full body exposure to the sun will trigger a delivery of up to 20,000 IU of vitamin D into the circulation over 48 hours. Vitamin D made in the skin also happens to last at least twice as long in the blood compared to vitamin D ingested from diet.

As you can see, while our bodies need vitamin D to function healthily, our modern lifestyles stop us from getting it. This is further compounded by the fact that the rainy season and the increasing amount of air pollution both reduce the amount of sunlight to absorb.

So when the sun is out shining brightly, embrace it. Get out there and get some vitamin D! Not to the point that you get burnt though as moderation is key. And if you need to supplement your sun exposure, take 2000 IU of vitamin D each day, doubling the dosage when you get sick. Happy sunning!


Sabetta J, Depetrillo P, Cipriani R, et al. Serum 25-Hydroxyvitamin D and the Incidence of Acute Viral Respiratory Tract Infections in Healthy Adults. PLoS One 2010;5(6):e11088.

Urashima M1, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren

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