Vitamin D And Flu Prevention | Strengthening Innate Immunity

In order to prevent any illness or disease, we first have to know its cause. Unfortunately, the US health care system doesn’t concern itself with causes. It spends its time and money developing pharmaceuticals for treating disease symptoms. This is why there hasn’t been a cure for any illness since…well…ever.

“What about polio, Dr. Mark? Let’s not forget THAT one!” 

I knew you would mention polio, but come on. That was sixty years ago, and there is still some debate as to whether the polio vaccine was actually the reason polio was eradicated. Statistics show that incidents of polio were already on the decline when the vaccine was released, and that many populations saw an INCREASE in polio following vaccination.

But even if we credit medicine for eliminating polio, has there been a cure for any disease since? I can’t think of one.

When it comes to the flu virus, science has shown that the flu shot is totally ineffective, so what are we to do about preventing the flu if there are currently no viable medical interventions? First, we have to uncover the CAUSE of the flu. Only then can we devise a plan for prevention.

Why the Flu Virus is Seasonal

Have you ever wondered why the flu virus is seasonal? Why does it only show up in the fall and winter months? Where does it go during summer? Does it only hatch in cold weather or something?

Your susceptibility to the flu virus has nothing to do with “germs,” the season, the people around you, or whether or not you’ve been vaccinated. It has everything to do, however, with the strength and efficiency of your immune system.

One study published in the New England Journal of Medicine, in which subjects were exposed to the common cold, showed that all individuals who exhibited symptoms of respiratory infection were under a level of stress high enough to depress immune function. (1)

People with strong immune systems simply do not get the flu.

Our immune systems take the biggest beating during fall and winter. The emotional stress of the holidays, the physical stress of colder temperatures, less exercise, less sleep, late-night parties, alcohol, sugary treats, etc., all play a role in weakening our defenses against illness and infection.

It’s also the time of year when our Vitamin D levels are lowest.

The Innate and Adaptive Immune Systems

The immune system is a complex network of hard-to-pronounce chemicals, microbes, and specialized defender cells that, when fully developed and functioning optimally, protects us from bacteria and viruses like a tank protects against a slingshot attack.

To better understand how we can strengthen our defenses against the flu virus, you must understand that the immune system has two parts:

1) The Innate Immune System

2) The Adaptive Immune System.

1. The innate immune system provides resistance against immediate threats. Its response is broad and non-specific. If you suffer an animal bite or puncture your skin on a rusty nail, the resultant swelling and mobilization of neutrophils, macrophages, and Natural Killer cells, all serve as a first line of defense against a wide range of bacteria and viruses. It’s basically like dropping a bomb on an enemy bunker.

2. The adaptive immune system, on the other hand, is much more specific. It responds by creating antibodies which attack a particular kind of bacteria or virus. If you had the chicken pox as a child, your adaptive immune system created special cells meant only for battling that particular infection in the future. You have this immunity for life. The adaptive immune system can also learn and improve its responses over time. It’s like hiring a hit-man for one specific person.

Strengthening Immunity Against the Flu

The flu shot is not liquid flu-killer. It’s an inactive flu virus, along with a cocktail of other chemicals, meant to ramp up your immune response so the correct antibodies are present to fight the infection if and when you come into contact with it.

How do they determine which flu strain to use for the vaccine? Using data from whatever flu strain was active in Asia that year, they guess!

The flu shot stimulates your adaptive immune system to create a defense against one particular strain of the flu virus.

Sounds pretty smart, right? But wait…

The active flu strain changes every year, so the antibodies you develop this year from a flu shot will be useless next year against the new strain. Your immune system will have to start over, creating a new set of antibodies for the new flu virus.

This ensures the need for a new flu shot each year to protect against the current flu strain, which is rarely ever matched correctly. Billions of dollars are made as a result of this cycle, even though the flu shot has been shown repeatedly to be unsuccessful.

Wouldn’t it make more sense to strengthen our innate immune system? The one designed to respond immediately to whatever flu strain is currently present? Would you rather send a hit-man to fight an invading army or just drop a megaton bomb on their base in the middle of the night?

Science Behind Vitamin D and the Flu

Many prominent scientists believe that a Vitamin D deficiency is the one and only cause of the flu.

Cold and flu season is indistinguishable from Vitamin D deficiency season. As sunlight plummets, so does our innate immune response, and incidents of flu infection skyrocket.

Statistics show this to occur both in the US and during the rainy season in the tropics.

♦ A study published in the Journal of Epidemiology and Infection (2) states that “3 independent research groups have recently shown that Vitamin D dramatically stimulates genetic expression of antimicrobial peptides (AMP) and other human cell lines.” These are our immune cells.

♦ The article goes on to say that “AMP display broad spectrum antimicrobial activity, including antiviral activity, and have been shown to inactivate the influenza virus.” 

You don’t produce these (AMP) without Vitamin D.

Another study, published in the Clinical Journal of the American Society of Nephrology, revealed several important facts. (3)

1. “Without Vitamin D, the ability of the cell to respond adequately to pathologic and physiologic signals is impaired.”

2. “Macrophages (immune cells) use Vitamin D to enable the synthesis of the bactericidal peptides needed to deal with bacterial and viral invaders.”

3. “Vitamin D dramatically up-regulates (turns on) the genetic expression of antimicrobial proteins (AMPs) in the immune cells of the innate immune system.”

That same sentiment, in almost the same language, was reiterated in another article published in the Journal of Epidemiology and Infection. (4)  Basically, without adequate amounts of Vitamin D, the immune system is severely impaired against fighting bacteria and viruses. 

In the American Journal of Clinical Nutrition (5)…

♦ A randomized, double-blind, placebo controlled study reported that children taking 1,200 IUs of Vitamin D per day in winter were 4x less likely to get the flu than those who were vaccinated.

♦ After 2 years of this study, they increased the dosage of Vitamin D in subjects to 2,000 IUs per day, and the incidents of colds and flu were reduced by almost 100%. Only 1 of the 104 subjects developed a cold or flu after that. 

This study, published in the Journal of Epidemiology and Infection, showed that a Vitamin D deficiency predisposes children to respiratory infections and that intervention with Vitamin D from cod liver oil reduced the incidents of respiratory infections in kids.

And this one, published in JAMA Internal Medicine and the largest study of its kind, concluded that sufficient levels of Vitamin D play a crucial role in innate immunity.

That’s not Enough! We Want More!

You want more? Okay, no problem…

T cells fight cancer. They also fight infection. They are absolutely essential for human immunity. Almost every function of the adaptive immune system (which we do still need) is controlled by T cells in some way. This study shows that if T cells don’t find enough Vitamin D, they won’t even mobilize.

And here is a collection of research confirming the dependence of the innate immune system on Vitamin D…

♦ In this study, Vitamin D deficiency resulted in more sick days from work due to respiratory infection.

♦ This one showed a strong correlation between newborns with low Vitamin D levels and the rate of respiratory infection. It suggested that expectant mothers supplement with Vitamin D during pregnancy to protect their baby against low Vitamin D levels.

♦ This one revealed that infants with low Vitamin D levels have higher risk of upper respiratory tract infections.

♦ And this one ties Vitamin D levels to immune function in kids.

Whew! I could go on, but if all this science hasn’t convinced you, another hundred references won’t either.

The good thing is that a Vitamin D supplement costs pennies per day and does not have to be administered by a health professional. It is probably the most effective and least expensive way to defend against infection and supply the body with an essential nutrient which most of us are severely lacking. It’s one of the 3 supplements I take every day.

If you’re constantly fighting colds and flu, or simply want better immune support, a quality Vitamin D supplement is always my first recommendation. The most recent scientific literature recommends 4,000 IUs per day for women, 5,000 IUs per day for men, and 1-2,000 IUs per day for children depending on age and size. *For best results, have your Vitamin D levels tested. 60-80 ng/ml is the ideal range.


  • 1. *Cohen, S. et al. (1991) N. Engl. J Med Aug 29; 325 (9): 606-12
  • 2. *Cannell, J. et al. Epidemiol Infect 134 (6) 1129-40
  • 3. *Heaney, R. Clin J Am Soc Neph. Vol 3 (5) 1535-41
  • 4. *Aloia, JF. Li-Ng M. (2007) Epidemiol Infect. 135 (7) : 1095-6; Author Reply 1097-8
  • 5. *Urashima, et al (2010). Am J Clin Nutr. Vol 91 (5) 1255-60