The ABCs of Vitamin D


As of today, either you or someone close to you is taking a vitamin D supplement.  Is it another trend?  Is it really needed?  Can I get it from foods?  Should I take a supplement?  How about my kids?  Should I get my levels checked?  So many questions and many confusing answers out there.  I will try to make it simple for you - as simple as the ABCs!

Vitamin D is a fat-soluble vitamin (along with vitamins A, E and K).  It is found naturally in very limited foods but added to many others.  You probably have seen it as a supplement everywhere you go!  

In addition, vitamin D can also be produced when UV rays from the sun hit your skin.  The truth is that no matter where you get it from; for the body to activate vitamin D - from either food, supplements or sun exposure; it has to go through hydroxylation.  This process has to happen not once, but twice!  Hydroxylation occurs in the liver (where it gets converted to calcidiol (25 (OH)D); and then in the kidney, where it becomes calcitriol (1,25-dihydroxy D) - the active form.

Vitamin D has many functions in the body.  For years, it has been known that it is essential in bone maintenance as it helps the balance of calcium and phosphorus in the body.  Calcitriol has a specific role – it boosts calcium and phosphorus absorption from the intestines and impedes the excretion of these by the kidneys.   

Today, more and more scientific studies are showing vitamin D’s role going beyond bone health.  Having a low vitamin D status has been linked to increasing the risk of a variety of chronic diseases.  These include but are not limited to hypertension, diabetes, limited muscular function, Alzheimer’s disease, Multiple Sclerosis, Parkinson’s Disease, decreased immunity, Crohn’s Disease, and cancer amongst several others.  Randomized trials are still needed to confirm some of these claims and observations, but the data is supporting these to be true.  Many experts believe that there is no question that having optimal vitamin D levels is beneficial.

You may wonder what your vitamin D level is.  If you don’t, you should.  I encourage you to ask your medical provider to include a vitamin D level on your next laboratory test.  Calcidiol or serum 25 (OH)D is the inactive form of vitamin D.  This is the form of vitamin D that we can find mostly in the blood and the level that needs to be checked when monitoring status (make sure that 1,25-dihydroxy D is not the one ordered to check your status).  The World Health Organization (WHO) defines vitamin D insufficiency as serum 25(OH)D below 20 ng/ml.  Recently, others started to define vitamin D deficiency as serum 25(OH)D level below 20 ng/ml and vitamin D insufficiency as less than 30 ng/ml.  The Institute of Medicine (IOM) is one of those who defines vitamin D deficiency as a level below 20 nmol/L.  They emphasize that this is the minimum level for the general population, excluding those who have conditions related to vitamin D.  The IOM has a higher threshold for what it considers vitamin D insufficiency – a serum calcidiol level below 50 nmol/L.  Many others, support the idea that a level of at least 80 nmol/L may be needed as a goal vitamin D level for the summer in order to prevent winter levels to go below 50 nmol/L.  

Having vitamin D insufficiency increases risks of problems with bone mineralization.  As a Registered Dietitian Nutritionist, I have seen a wide variety of conditions across the lifespan and have to agree with the level markers from the IOM.  It may be unclear if vitamin D provides more health benefits than those of bone mineralization.  For me, that is sufficient to aim at maintaining optimal levels – not above deficiency but above insufficiency.  Unfortunately, a large part of the population (this may include you!), even children, do not meet those optimal levels.  Many groups are even at higher risk of not reaching their vitamin D needs.  The Vitamin D Council describes these groups as: people with darker skin, people who spend a big part of their day indoors, people who live in the north part of the USA or Canada (further away from the equator), people who cover their skin all or most of the time, older people, pregnant women, infants who are breastfed and are not given a supplement, people who are overweight or obese.  

Different organizations have different recommendations of how much vitamin D we need each day.  These amounts vary significantly.  Some believe that evidence is still lacking to support higher doses of vitamin D, while others feel strongly that more is needed to prevent deficiency.  The IOM uses the Dietary Reference Intakes (DRI).  DRIs are given to as a guide for good nutrition for a healthy population, not to correct deficiency or insufficiency.  Side by side you can see the recommendations from the IOM, The Vitamin D council and The Endocrine Society.  

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How should I meet my vitamin D needs, you may ask?  Well, sun exposure can provide good amounts of vitamin D for some people.  A light-skinned individual with full body-exposure for 15 minutes at noon in the summer, may trigger a release of 10,000 of vitamin D.  For a dark-skinned person, that would only create about 5,000 IU.  At the same time, these values may be different from one individual to the next and they are affected by many other factors, like location, time of day, etc.  The downside is that we are all aware of the damages caused by excessive sun exposure, especially unprotected!  For this reason, relying on sunlight to meet our vitamin D needs may not be always the best choice.

You should know that Vitamin D is naturally available in some foods.  But, choosing products that are fortified or enriched, is another helpful way of getting your vitamin D.   Here are some of the foods with higher amounts of vitamin D.

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Vitamin D is also available in supplements and most multivitamins contain a good amount (400-1,000 IU).  You can easily find commercial supplements ranging from 400 IU to 50,000 IU per serving.  There are gummies, gel caps and even liquid formulations available.  For many, supplements may be a necessity to ensure that the minimum recommendations are being met.  If deficiency or insufficiency is already existent, supplementation is going to be essential in order to correct those levels.  

If you think that your child, spouse or even yourself struggles meeting the daily recommended vitamin D intake, strongly consider visiting a Registered Dietitian Nutritionist to work on intake recommendations that will emphasize foods rich in this important nutrient.  If you believe that a supplement may be necessary, check with your medical provider to choose the right dose for you.  

Hope that you now know your ABCs and feel more comfortable about vitamin D!  


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