It is not uncommon these days for their healthcare practitioner to recommend a vitamin D supplement, even though there are no signs of vitamin D deficiency.[vii] Nevertheless, this gets us thinking…why? Is there a problem? Do I have vitamin D deficiency? It is always best to clarify and discuss this with your healthcare professional. It is also a good idea to learn more. Our Ddrops fans often ask us many questions about vitamin D, so read more in our blog series about vitamin D deficiency.

How do people know if they are low in vitamin D?

Experts define vitamin D deficiency in terms of blood levels.  There are different degrees of low vitamin D blood levels that characterize the range of vitamin D deficiency, and these categories vary from country to country and region to region.  To confuse things even more, the blood test is reported in different values for different countries.  There are other blood tests (i.e. calcium, phosphorus, 25(OH)D, etc.)  and sometimes a bone scan is also considered.  Physicians will typically do a physical examination, with special attention to bone formation, muscle strength and they may ask about tenderness.

The vitamin D blood test:[i]

Medical professionals determine whether somebody is vitamin D deficient or not by doing a simple blood test.  The blood test is actually designed to look for a marker of vitamin D in the circulating blood, 25-hydroxyvitamin D or 25(OH)D₃ or 25(OH)D (calcidiol) – the major metabolite of vitamin D₃ found in the bloodstream.  In the United States, most vitamin D lab results are reported in ng/mL.  In Canada and the UK, values are reported in nmol/L.  (see the table below).

Some people lack vitamin D more than others, therefore experts have developed a ‘vitamin D nutrition status’ scale. In Canada, the sufficiency cut-off is higher than in the US and UK. The table below describes the range of vitamin D and health in North America.

United States: Serum 25-Hydroxyvitamin D [25(OH)D] Concentrations and Health*[ii]

Serum 25(OH)D₃ range Vitamin D nutritional status
>50 ng/mL (>125nmol/L) Evidence links potential adverse effects to such high levels, particularly >150 nmol/L (>60 ng/mL)
>20 ng/mL (50 nmol/L) Sufficiency  (desirable optimal for fracture prevention)
12-20 ng/mL (30-50 nmol/L) Insufficiency
<12 ng/mL (30 nmol/L). Deficient (diagnostic of nutrition deficiency, rickets or osteomalacia).

Conversion Factor for nmol/L: ** 1 nmol/L = 0.4 ng/mL

Canada: Circulating levels of 25- hydroxyl-Vitamin D or 25(OH)D₃ by vitamin D nutrition status[iii]

Serum 25(OH)D₃ range Vitamin D nutritional status
>600 nmol/L (>240 ng/mL) Vitamin D toxicity
<225 nmol/L (<90 ng/mL) Physiologic range from exposure to sunlight (or UV light)
<75 nmol/L (>30 ng/mL) Sufficiency  (desirable optimal for fracture prevention)
<40 nmol/L (<16 ng/mL) Insufficiency
<25 nmol/L (>10 ng/mL) Deficient (diagnostic of nutrition deficiency, rickets or osteomalacia).

Conversion Factor:  ng/mL x 2.5075

So what is the optimal vitamin D level?

Good question!  The answer is not as easy because there are differences in opinions about what a “vitamin D deficiency” is and what is “vitamin D insufficiency”. Why these two classifications anyway? A wide “optimal” range for vitamin D blood levels or 25(OH)D is reported  between 25-80 ng/mL or 50 nmol/L – 225nmol/L.[iv]

To test vitamin D blood levels… or not test? That is the question!

In some regions, for example in Canada, physicians do not routinely test vitamin D blood levels on healthy individuals, unless they suspect vitamin D deficiency.[v] But why? Many Canadians are low in vitamin D, and health authorities recommend that people should focus on getting enough vitamin D either naturally and/or with supplementation, instead of going to the trouble and cost of having a blood test. Some healthcare professionals guided by their practical experience recommend empiric vitamin D supplementation, without testing, to patients who have no obvious risk factors or signs of deficiency[vi]. This is the same with infants. This is likely because their patients generally have inconsistent or limited daily sun exposure and/or they have little vitamin D intake in daily food.  Vitamin D blood tests can be helpful for healthcare practitioners to evaluate a suspected case of vitamin D deficiency and allow them to diagnose, monitor and treat the condition if necessary. Talk to your healthcare practitioner about your individual vitamin D status and needs.  Remember, Ddrops® products are not indicated to treat or correct vitamin D deficiencies; Ddrops® are intended to help maintain healthy blood levels of vitamin D.

Looking to read more on vitamin D deficiency? Check out the rest of our series here.

[vii] Kennel et. al. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clin Proc. 2010 Aug; 85(8): 752–758.

[i] 25-hydroxy vitamin D test. NIH Medical Encyclopaedia

[ii] Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.

[iii] Hospitals In-Common Laboratory Inc.

[iv] Kennel et. al. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clin Proc. 2010 Aug; 85(8): 752–758.

[v] Understanding Changes to OHIP Coverage of Vitamin D Testing OHIP 2010

[vi] Kennel et. al. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clin Proc. 2010 Aug; 85(8): 752–758.