Do you know which nutrient can lower the risk of common cold and also, potentially, of heart disease, diabetes, cancer, and tuberculosis?

No, it’s not vitamin C or any other antioxidant you had in mind.

Hint N1: it is the ONLY supplement I universally recommend to all my clients, subscribers and readers

Hint N2: it also helps our bones absorb more calcium.

It is vitamin D, of course!

Some interesting facts about vitamin D: 

  • it is not a vitamin, it is a prohormone produced in our skin when it is exposed to the sun
  • until a few years ago, we did not know much about vitamin D outside its effect on bone health
  • many countries around the world have updated their recommendations in the last few years, including the US, Canada and UK
  • when your shadow is longer than your height – you are not making any vitamin D
  • if you live in the northern hemisphere, your body does not produce vitamin D between September and April
  • To produce enough vitamin D, we need to spent 5-30 minutes between 10 am and 3 pm at least twice a week with the face, arms, legs or back exposed to direct sun, not covered by clouds  
  • we do not absorb vitamin D if we cover our bodies with sun cream, clothes or receive the sunlight through a window

What do we know about vitamin D and immunity?

A systematic review and meta-analysis published in the British Medical Journal looked at whether vitamin D supplementation could prevent acute respiratory tract infections such as flu, bronchitis, and pneumonia.

The study’s main findings:

  1. Vitamin D supplementation is protective against acute respiratory tract infection
  2. The protective effect was stronger in those who were initially deficient in vitamin D and those who were getting regular daily or weekly doses rather than a bigger dose once a month or every three months. 

Is it high-quality evidence?

The review included only randomized control studies, the highest standard in the research world. Funding was provided by the National Institute for Health Research, no vitamin D supplement companies were involved in the research.  

Who decides how much vitamin D we need?

In the UK – Scientific Advisory Committee (SACN) on Nutrition and Public Health England

In the US – Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies

As you see below, the recommendations between the two countries differ. Confused? You should be. At this point, we are just waiting for scientists to agree on how much vitamin D will help bring the blood levels to an optimum level. 

The good news is that even the highest of the recommended amounts is very far from the Upper Limit of vitamin D and is safe to take. 

Age UK Recommendations
0-6 months 8.5 mcg or 340 IU
7m – 3 y 7 mcg or 280 IU
4-50 y 10 mcg or 400 IU
51-64 y 10 mcg or 400 IU
65-70 y 10 mcg or 400 IU
71+  10 mcg or 400 IU


Age US Recommendations 
0-12 m 10 mcg or 400 IU
1-13 y 15 mcg or 600 IU
14-18y 15 mcg or 600 IU
19-50 y 15 mcg or 600 IU
51-70 y 15 mcg or 600 IU
70 y + 20 mcg or 800 IU

Does your child need vitamin D supplement? It has been shown to improve immune function and prevent common cold.

Can we get vitamin D through diet?

A simple answer: No.

 On average, we can only achieve about 3.5 or 140 IU through diet, even if we eat in a perfectly balanced way. 

First of all, very few foods in nature contain vitamin D. Some foods like cereals and juices are fortified with vitamin D but you would have to eat a lot of them in order to achieve the recommended amount. 

To put things into perspective, your 4-year-old would need to eat a 3oz fillet of salmon every day or drink 10 glasses of milk, eat 10 eggs or 3 cans of tuna in order to achieve the recommended amount (400 IU in the UK).  

It may be slightly easier to get your vitamin D from food if you live in the US because some brands of milk are voluntarily fortified with vitamin D. 

NOTE: Infant formula is fortified with the recommended amount of vitamin D both in the UK and US. 

Who needs to supplement their diet with vitamin D?

At this point, it is safe to say that any child or adult who is not drinking fortified formula and lives in the northern hemisphere needs a vitamin D supplement.

How to choose a vitamin D supplement?

  1. Vitamin D supplements come in a variety of forms: drops, sprays, capsules and a part of comprehensive multivitamin pills. Choose the form that works the best for you and your child. I personally like vitamin D sprays, they are very easy to use and my kids love doing it themselves, usually at breakfast. If you or your kids take a comprehensive supplement, check how much vitamin D it includes and get a separate vitamin D supplement if needed.
  2. Choose the animal form of vitamin D (D3) over the plant form (D2). The animal form has been shown to be more effective in raising blood levels of vitamin D.

Do you have any questions about vitamin D? Is there anything else I should add to this article? Please let me know in the comments!

You may also like:

Top 6 nutrients for children and their food sources

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How to help your dairy-free child meet his calcium needs?

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Martineau Adrian R, Jolliffe David A, Hooper Richard L, Greenberg Lauren, Aloia John F, Bergman Peter et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data BMJ 2017; 356 :i6583

Laura Tripkovic, Louise R Wilson, Kathryn Hart, Sig Johnsen, Simon de Lusignan, Colin P Smith, Giselda Bucca, Simon Penson, Gemma Chope, Ruan Elliott, Elina Hyppönen, Jacqueline L Berry, Susan A Lanham-New; Daily supplementation with 15 μg vitamin D2 compared with vitamin D3 to increase wintertime 25-hydroxyvitamin D status in healthy South Asian and white European women: a 12-wk randomized, placebo-controlled food-fortification trial, The American Journal of Clinical Nutrition, Volume 106, Issue 2, 1 August 2017, Pages 481–490,

Lanham-New, S. The secret of sunshine all year round: the forgotten nutrient. British Nutrition Foundation Talk, July 2017. Available online at

Vitamin D. Fact Sheet for Health Professionals. Office of Dietary Supplements. Available online at