Vitamin D supplement. Cholecalciferol

Vitamin D, Colds & The Flu. Oh My!


Colds are big business. In the United States (and proportionately similar here in Canada no doubt) Americans suffer their way through about 1 billion respiratory infections each year (yup, if you’re doing the math, most people get 2-3 ‘colds/flu’ per year; some poor souls even more).


They spend about 2 billion dollars on non-prescription cold and cough remedies with over 1 billion doctor visits. That’s a ton of coughing, sniffling and post-nasal drip.


Statistics are hugely variable but:

  • 5-20% of the US population will get the flu (notice most people don’t say they have a ‘cold’ but rather everyone has the ‘flu’)
  • 200,000 are hospitalized each year due to flu-related complications
  • 3,000-49,000 will die from those flu-related complications in the US, about 350,000 worldwide
  • It takes 1-4 days for symptoms to start to show up after infection if your immune system doesn’t beat it – yes, just because you’re exposed doesn’t mean you will become as sick as a dog. News flash, the flu, and cold viruses ARE NOT only around during the winter, but we’re also exposed to them EVERY SINGLE DAY, 365 days a year
  • Most of us are contagious about 1 day before symptoms start to show and continue for about 5 to 7 days after that
  • Peak flu & cold season in North America is from the beginning of December to the end of February


If there was something that could support your defenses against these intruders, something that not only helps the very response your immune system takes against these unwanted guests that could also improve your mood, reduce the risk for several cancers, and help your bones wouldn’t you want to take it?

Vitamin D, colds and flu

In a 2010 prospective study, researchers wanted to further explore the observation that acute viral respiratory tract infections increase during the late fall and throughout winter and the theory that this is linked, in part, to plummeting vitamin D concentration in the blood.


In this study, researchers looked at vitamin D concentrations in 198 healthy adults at the end of the summer (3rd week of Sept) and then monthly during the fall and winter in 2009-2010; the patients were blinded to what was being measured so they did not know their vitamin D concentration was being tested.


At each monthly visit, subjects were asked about their medication use, herbal products, vitamin, mineral, and other supplements use and if they received the 2009/2010 flu vaccine; no differences were reported among participants. Those who reported and presented with symptoms were swabbed for viral identification/confirmation.


New respiratory infections in participants were tracked along with their blood levels of vitamin D. Researchers wanted to know how vitamin D levels at the end of the summer and throughout the fall and wintVitamin D supp 300x225 - Vitamin D, Colds & The Flu. Oh My!er influenced the length of time it took to develop a respiratory infection, as well as, determine how many of the subjects didn’t get sick.


There was a clinically significant, two-fold (halved) lower risk of developing a respiratory infection with vitamin D concentrations of 95 nmol/L (38 ng/ml) or more. The effect size was so large that it was shown to be statistically significant (i.e. we can confidently accept the results) even though the sample size was small.


Great news!

Vitamin D reduces chance of viral infections - Vitamin D, Colds & The Flu. Oh My!


It’s important to note that those who maintained high levels of vitamin D concentrations throughout the fall and winter were taking supplements. Vitamin D concentration in the blood is normally reduced by half every 8 weeks or so, something called ‘half-life’ so even those who leave the summer with a robust amount of vitamin D in their blood will be deficient by the end of December.


The author’s concluded that “maintenance of a 25-hydroxyvitamin D serum concentration of 95 nmol/L (38 ng/ml) or higher should significantly reduce the incidence of acute viral respiratory tract infections and the burden of illness caused thereby, at least during the fall and winter in temperate zones [i.e. north of 37 degrees latitude see map below]

Vitamin D winter - Vitamin D, Colds & The Flu. Oh My!


Other vitamin D studies on colds and flu

Vitamin D has been studied for its role in supporting the immune system in its fight against colds and flu.


Vitamin D is a pro-hormone that the immune cells can’t get enough of. They purposefully have vitamin D receptors; once docked, vitamin D helps the immune cells to increase their production of some 200 naturally-occurring antimicrobial proteins which is why vitamin D helps to fight respiratory infections, as well as, other pathogens and cancer cells in their early development.


A 2010 study in Japan demonstrated that 1200 IU of vitamin D per day resulted in a 64% reduction in influenza A in Japanese school children.


Another 2012 study in Sweden looked at whether vitamin D supplementation could reduce infectious symptoms and antibiotic use in those with antibody deficiency or in whom routinely have frequent respiratory tract infections; vitamin D reduced disease burden. For more, check out the Vitamin D Council’s section on respiratory infections.


The latest study from the British Medical Journal looked at the impact of vitamin D supplements and corresponding vitamin D concentration in the blood and found that daily or weekly supplementation had the greatest benefit for individuals who were outright vitamin D deficient (<10 nmol/L) or for those with vitamin D concentrations typically seen in late fall and throughout the winter: 25 nmol/L. Vitamin D supplementation cut the risk for respiratory infections cut by half in those poor folk.


Studies consistently find that occasional high doses of vitamin D such as 1x/month or every 3 months did not produce benefits. 


Similar findings have been shown over at Grassroots Health. Participants in their ongoing prospective study record their vitamin D intake/supplement use, have blood concentrations done and report on several health conditions every 6 months. They’ve found that higher levels of vitamin D are routinely associated with and predictive of fewer colds and flu.

Cold flu vit D Grassroots Health - Vitamin D, Colds & The Flu. Oh My!

Bottom line

There’s no debate that vitamin D is needed for a healthy immune system and that maintaining higher blood concentrations can reduce the risk for colds and the flu.


This isn’t to say that you should avoid the flu shot, that’s a personal decision but know that research shows vaccines are more effective with more vitamin D on board; antibody production is improved which makes sense since vitamin D (as well as several other nutrients like vitamins A, C, E, and zinc) helps the body in this effort.


Ideally, you would get your vitamin D tested and take the appropriate amount of vitamin D needed to raise your personal concentrations to what research has shown to be helpful; everyone responds differently so tailored dosing really is ideal.


A health practitioner who’s informed on this can help you. Getting more vitamin D would be a smart thing to do to help get you through the cold and flu season – but no amount of dietary vitamin D will be able to do this.