The Low Down on Vitamin D Supplementation

The Low Down on Vitamin D Supplementation

Vitamin D has been touted as a cure-all by the health media 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.

So few articles and reports on vitamin D provide the facts as well as clear, safe suggestions on vitamin D supplementation.

D2, D3, D what?

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. Vitamin D2 is the vegetarian version and it’s widely accepted that it is not as potent as vitamin D3. D2 is used to fortify non-dairy beverages.

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 2000 genes throughout the body.

Vitamin D can influence so many different genes and cells that it has such a positive impact on a wide variety of health issues.

Vitamin D3 (or ‘vitamin D’ for this article) is converted to 25(OH)D in the liver. 25(OH)D 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.


The primary source of vitamin D is the sun, but there are a couple of caveats: only UVB can produce it and anything that blocks UVB will also 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 longer the ‘vitamin D winter’ can be (a period when the body cannot produce its own due to lack of sunlight).

Most people simply don’t spend enough time outdoors even during peak vitamin D absorption times. For those of European decent, enough vitamin D could be made in about 10-15 minutes, but only if 40% of the body surface is exposed to sunlight between the hours of 11am and 2pm. For someone of African/Caribbean decent, it could take up to 2 hours, but that amount of exposure alone would produce about 10,000IU!

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 10,000IU per day 1. It is important to note that any concerns about vitamin D should be addressed with your healthcare practitioner prior to taking supplements.

You still might be asking yourself at this point, “how much should I take?” Experts suggest that the answer lies in whatever it takes to raise your blood level to optimize health, which is why it is important to contact your healthcare practitioner first.

Great debates continue over what should be considered the “ideal” blood level of vitamin D, but some basic facts point the way: maximum calcium absorption is reached at 32ng/L (80nmol), and significant suppression of Parathyroid Hormone or PTH (responsible for bone turnover) really begins at 50ng/L (125nmol). PTH is a hormone that is released when blood calcium levels dip as 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 experts advocate to strive for levels of those living in sun-rich countries; 50-60ng/L (125-150nmol). The majority of health professionals agree that the absolute minimum level of vitamin D is around 30ng/L (75nmol).

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 30ng/L (75nmol). 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 study found that current recommendations are not enough to maintain blood levels of vitamin D. The authors concluded:

to achieve 25(OH)D over 30ng/L or 75 nmol/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.

So what’s the bottom line?

Experts in the field suggest that deficiency, as defined as below 30ng/L (75nmol) is the norm and not the exception. Judicious sun exposure, when there is enough UVB, will most likely only satisfy those with fairer complexions. Even still, 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. 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 of vitamin D to where they should be. Supplementation is really the only viable option for the vast majority of the population. Essentially all people (98%) living in the US north of boston or 42 degrees latitude, 2000IU per day will achieve 80nmol, the minimum level needed to maximize calcium absorption, to get to 120nmol, 4000IU per day is likely needed. This amount can be decreased to 1000-2000IU per day during the late spring and summer provided you are getting enough safe sun exposure, if not, then 4000IU per day year round will be required. Aim to get the current upper level of the DRI (Dietary Reference Intake) of 2000IU per day, this will ensure that most will reach the minimum of goal of 30ng/L (75nmol). Most people would benefit from much more, 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.


1] Zoltan, R. M.D. (2010)

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Doug Cook, RD MHSc is a Registered Dietitian Nutritionist and Diabetes Educator who uses a holistic and science-based approach to his practice.