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Ask a Nutritionist: How much vitamin D is enough?

By Nonie DeLong, ROHP, CNP

Dear Nutritionist,

Thank you for your articles. I would like to know if you can speak to vitamin D and whether it’s beneficial to supplement with it. If it is, how much should a person use?

Thank you,


Dear Angie,

Vitamin D is a nutrient that’s received a lot of press in recent years, so some readers might be tempted to think there’s nothing more to say about it. But whenever there is a lot of interest in any nutrient or food there is also a lot of conflicting information about it to sort through. And vitamin D is no exception. Did you know it can be potentially toxic? So, Angie, your question will be helpful to a lot of people. Thank you for writing in!

What is vitamin D and how do we get it?  

Well, for starters, it’s technically not even a vitamin. And it’s not singular. It’s a group of hormone precursors, very similar in structure to steroid molecules. As many readers may already know, the most important players in this group (as we currently understand it) are vitamins D2 (ergocalciferol) and D3 (cholecalciferol).

Vitamin D3 is so essential for our health that we have a built in mechanism to ensure we get enough, irrespective of dietary intake. It’s actually manufactured by our bodies when our skin is exposed to UVB rays from the sun. This synthesis requires our own cholesterol and activation by our liver and kidneys. It’s unique among vitamins, not only because we generate it from the sun, but also because almost every cell in our bodies has a vitamin D receptor, which has the ability to impact the expression of our genes. This is science we are just starting to understand, but it indicates this little secosteroid is essential in a way no other nutrient is.

Animal foods are the best source of vitamin D3, but dietary consumption alone is not enough to reach optimal levels. It’s present in certain fish, fish oils, liver, and quality egg yolks, quality butter, and – dare I speak it – raw, whole fat milk from grass fed cattle. I mention this because raw milk contains every known fat and water soluble vitamin, all 18 fatty acids, and multiple enzymes and probiotics to aid digestion – all of which are almost completely destroyed by pasteurization. But selling raw milk is illegal in Canada so let’s do forget I said that and keep moving along.

We can get vitamin D2 from mushrooms that have been exposed to UV rays, fortified foods, and lower quality supplements. But it’s not the desired form of this hormone group for therapeutic value. You can check the label of your dairy and baby formula products to see which form of vitamin D they contain, and then take that with a grain of salt. According to this study published in the New England Journal of Medicine, we don’t really know how much vitamin D – or which form – is being added to our fortified products. Note that most of the infant formula tested contained 200x or more vitamin D than was on the label. With fortified foods it’s hard to know what exactly you’re getting.

What does vitamin D do?

Vitamin D is best known for its role in bone and dental health. Without adequate vitamin D children can develop rickets, and adults are at risk of premature bone ageing and resulting fractures, as adequate vitamin D is needed for calcium, phosphate, and magnesium absorption and regulation. These play a direct role in bone growth and density, as well as neuromuscular function, immunity, and inflammation. Additionally, vitamin D helps regulate hormones and has a positive impact on mood, concentration, learning, and memory.

Vitamin D also helps keep abnormal cells from multiplying in breast and colon tissues. Isn’t it interesting how these cancers have proliferated since the campaign to push sunscreen? Vitamin D synthesis can’t happen in the presence of sunscreens with SPF 15 or higher. There is additional data to support that vitamin D deficiency increases our overall risk of cancer and our risk of melanoma, the deadliest type of skin cancer. Low vitamin D levels are associated with a number of serious diseases:

“A growing number of studies point to vitamin D deficiency as a risk factor for heart attacks, congestive heart failure, peripheral arterial disease (PAD), strokes, and the conditions associated with cardiovascular disease, such as high blood pressure and diabetes,” according to John Hopkins Heart and Vascular Institute.

How much do we need?

The Canadian government Dietary Reference Intake for vitamin D is between 600-800IU on the low end to 4000IU on the high end for adults. But serum 25-hydroxy-vitamin-D testing is still the best way to know your vitamin D status. The upper end of the optimal range is 50nmol/L. <30nmol/L means you’re suboptimal and between those two you may need to supplement accordingly. To give you an idea of safety, levels >125nmol/L are considered a possible reason for concern.

Certain populations are known to be more likely to be deficient in vitamin D and should be supplementing with the guidance of a professional and annual testing to determine blood levels. At risk populations include:

  • those over 65 – older skin often doesn’t produce as much vitamin D as it used to
  • those with darker skin tones – it takes more sun to synthesize the same amount of vitamin D in darker skin
  • those who work indoors, wear sunscreen all the time, or cover much of their skin when outside
  • those who live in places where the sun’s rays are weaker and/or they don’t get as much exposure to the sun for good parts of the year
  • those who have a gastrointestinal condition like Crohn’s disease or celiac disease or who have bile issues (both important for vitamin D synthesis and uptake)
  • those who are vegetarian or vegan (animal products are the best sources of the active form of vitamin D if they don’t get enough sun exposure or supplement)
  • those who have severe kidney disease (the kidneys have to convert it to the active form)
  • those who have to avoid the sunlight for other medical reasons
  • those who do shift work

It’s estimated that in the U.S. up to 90% of those with darker skin tones and 75% of those with lighter skin are deficient in this key hormone, so in Canada we are likely to be even more deficient, due to our latitude and cold winters.

Are there any safety concerns?

Yes. Fat soluble supplements are stored in the tissues so they build up over time. As such, toxicity can develop and it’s best to stay below the safe upper limit and have your physician test your levels annually as part of your check up.

How do I best get it?

It’s almost always best to get vitamin D from sunlight – as we were designed to. Research on supplementing with vitamin D has not demonstrated the same protective benefits as we theorize that it should. It may be possible that supplementing does not do what sunlight does for us. There could be unrecognized cofactors we need for optimal conversion and utilization. In addition sunlight has many other benefits for our health.

“But sunscreen!” I can hear you quip. It’s outside of my scope to speak to the supposed dangers of the sun but I would like to say I have yet to read any data that demonstrates that before sunscreen humans were dropping like flies of skin cancer, which has now been ameliorated by our religious use of sunblock. So, in my humble opinion and clinical practice, I advocate the use of short periods of almost full body exposure to full spectrum, natural sunlight or quality tanning beds with proper protective wear and timing to prevent burning. Or you could have a backyard bikini BBQ. Bikini optional!

My preference when I do advise clients to supplement is to use quality, sustainable cod liver oil (CLO) as this is a whole food supplement with vitamins A and D in the proper ratios (4-8x the A to D), as well as EPA and DHA omega 3s for maximal benefit. It’s theorized that this A:D ratio helps protect against vitamin D toxicity. Add a daily dose of vitamin K2 in the form of Emu oil or natto and you have done more to protect your bones and hormones than anything else you can do.

As always, if readers have their own health questions, I welcome them. Feel free to reach out through the Ask a Nutritionist page. And if you’re looking for more specific health information check out my website and sign up for my free newsletter at hopenotdope.ca. I provide comprehensive health coaching and several group classes, all available online for safety and convenience.


Nonie Nutritionista

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