The Low Down on Vitamin D Supplementation


Vitamin D sources including food and sun


It seems you can’t turn on the TV or open the newspaper without being hit with another story about the wonders of vitamin D. It has essentially been touted as a panacea for most of the chronic diseases that afflict humanity: diabetes, osteoporosis, multiple sclerosis, breast, colon and prostate cancer, autoimmune diseases, influenza, colds and North America’s number one killer, cardiovascular disease.


While there is a lot of information buzzing around the internet, there is also a lot of confusion as well. This article will aim to give the facts as simply as possible while giving some clear and safe suggestions on how to take advantage of this important nutrient.


Vitamin D2 or D3. What’s in a name?

  • For the purpose of general nutrition, the term vitamin D is used to refer to either D2 (ergocalciferol) or D3 (cholecalciferol).
  • D3 is what’s produced by the skin upon exposure to sunlight (adequate UVB), found in some foods, and in supplements. D2 is the vegetarian version and it’s widely accepted not to be as potent as D3. D2 is used to fortify non-dairy beverages.
  • Vitamin D3 (or ‘vitamin D’ for this article) is converted to 25(OH)D in the liver. This is regarded as the body’s storage form of vitamin D and if you are going to get your vitamin D tested, this is what you want looked at, not 1,25(OH)D.
  • Vitamin D is not a vitamin; it was misclassified as a vitamin when it was discovered in 1922. It is a pro-hormone. Various cells throughout the body are capable of converting vitamin D into its active hormone form which modulates over 200 genes throughout the body
  • It is because vitamin D can influence so many different genes and cells, that it has such a wide positive impact on a variety of health issues. Because it is still referred to as a vitamin, many think of it in those terms, and as such, are still convinced that only small amounts are required.


A can of sardines



  • The primary source of vitamin D is the sun. There are a couple of caveats: Only UVB can produce it. Anything that blocks UVB will block vitamin D production; this includes windows, smog, clothing, sunscreen, complexion and age (older adults are not as efficient at producing it).
  • Depending on where you live in North America, there may be insufficient UVB from one to six months during the fall and winter – the further away you are from the equator, the long the ‘vitamin D winter’, the period when the body can not make any.
  • The reality is that most people today simply don’t spend enough time out doors even in the summer. Even so, for those with European decent, enough vitamin D could be made in about 10-15 minutes but only if 40% of the body surface was exposed between the hours of 11am and 2pm. For someone of African/Caribbean decent, it could take up to 2 hours. By the way, this would produce about 10,000 IU!


What is the ideal blood level and dose?

  • Vitamin D is actually extremely safe and there has never been a reported case of toxicity from supplement use up to 10,000 IU per day.
  • Experts suggest that the answer to ‘how much should I take’ is this: what ever it takes to raise your blood level to optimize health. Great debate rages over what the ideal blood level of vitamin D should be but some basic facts point the way – maximum calcium absorption is reached at 80 nmol (32 ng/L), and significant suppression of parathyroid hormone or PTH (responsible for bone turnover), really kicks in at 125 nmol (50ng/L).
  • PTH is a hormone that is released when blood calcium levels dip where it helps to raise calcium levels by simulating bone breakdown and releasing calcium. This is normal and desirable as bone is constantly being broken down and rebuilt. Excessive bone break down is not a good thing. Vitamin D aids in dietary calcium absorption (maintaining blood calcium levels) which helps to slow down PTH release but vitamin D also helps to directly suppress PTH release by the parathyroid gland.
  • Some advocate to strive for levels of those living in sun-rich countries; 125-150 nmol (50-60 ng/L). The majority of health professionals agree that the absolute minimum level is around 75 nmol (30 ng/L).


A recent study published in the Journal of Nutrition helps to shed light on this very issue. In a nutshell, the study’s goal was to see how much extra vitamin D would be needed to achieve a 25(OH)D level of 75 nmol (30 ng/L). The study took into account sun exposure over the year and it grouped the subjects into two groups: African ancestry and European ancestry. It then categorized the groups into low and high sun exposure. The results? Current recommendations are not enough to maintain blood levels of vitamin D. The authors concluded


“to achieve 25(OH)D over 75 nmol/L or 30 ng/L, we estimate that European ancestry individuals with high sun exposure need 1300 IU/d vitamin D intake in the winter and African ancestry individuals with low sun exposure need 2100-3100 IU/d year-round”


Sun and sunflower_Nick Booth

So what’s the bottom line?

Experts in the field suggest that testing might not even be required, deficiency, as defined as below 75 nmol (30 ng/L) is the norm and not the exception. Judicious sun exposure, when there is enough UVB, will most likely only satisfy those with fairer complexions.


Regardless most of us simply do not have the time to expose enough of our bodies several days of the week to ensure we are getting enough of this vital nutrient. Even those entering the fall and winter with adequate levels from the summer will soon find that not to be the case by the following January.


Food sources are simply not enough to consistently raise blood levels to where they should be. Supplementation is really the only viable option for the vast majority of the population. For essentially all people (98%) living north of Boston, 2000 IU per day will achieve 80 nmol, the minimum level needed to maximize calcium absorption, to get to 120 nmol, 4000 IU per day is likely needed.


This amount can be decreased to 1000-2000 IU per day during the late spring and summer provided you are getting enough safe sun exposure, if not, then 4000 IU per day year round will be required.


Aim to get the current upper level of the DRI (Dietary Reference Intake) of 2000 IU per day at the very least, this will ensure that most will reach the minimum of goal of 75 nmol (30 ng/L). Most people would benefit from much more [the suggested adult dose is 4000-5000 IU/day], which is why testing is critical. In the mean time, we will have to wait for the Institute of Medicine’s report on the revised recommendations for vitamin D, due out in May 2010.


Update: In November 2010, the IOM announced the new RDA for vitamin D as 600 IU/day for adults; considered to be a paltry amount by most experts. This is estimated to get most of the population to 50 nmol/L or 20 ng/L which the IOM feels is adequate however this will leave 25-30% of the population with some osteoid tissue. Osteoid tissue is bone tissue that is not fully mineralized with calcium, phosphorus or magnesium. Why the IOM feels this is OK, is baffling to most including myself. On a more positive note, the IOM raised the UL for vitamin D to 4000 IU/day. People can confidently take this amount knowing it will help to ensure 98% of the population will get to 80 nmol and some will reach 100 nmol/L


Photo credit: istockphotoNick Booth


Doug Cook RDN is a Toronto based integrative and functional nutritionist and dietitian with a focus on digestive, gut, and mental health.  Follow me on FacebookInstagram and Twitter.

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