Several of patients whose vitamin D level is checked by their primary care physician or by me have low levels.
Here are the vitamin D levels from some of my current patients:
How do we decide what is a “normal” vitamin D level?
So, I began to wonder if it is the “normal” range noted on the laboratory test reports that needed to be changed. After all, I thought, if so many people have low levels, then what does “normal” mean?
It has been estimated that over 50% of all people in the world have low vitamin D levels. Isn’t that unbelievable! Or, in the UK, about 20% of the population.
Here’s the answer. “Normal” is defined based on the association of intake and serum levels of vitamin D with various problems.
If the serum level of vitamin D is less than 12 ng/mL (or 30 nmol/L), the person may develop rickets or osteomalacia (Bouillon and Carmeliet, 2018). So, it makes sense such serum levels or daily intake should be considered to indicate severe vitamin D deficiency.
If the serum level of vitamin D is below 20 or 30 ng/mL (50 to 75 nmol/L), the person is at increased risk of fractures and some other negative outcomes like falls in elderly persons (Bouillon and Carmeliet, 2018). So, these serum levels are considered to indicate a low vitamin D level.
Vitamin D “insufficiency” versus “deficiency”
The term “insufficiency” means a mild decrease and “deficiency” means a greater decrease in vitamin D levels.
– Normal vitamin D levels are a serum 25-hydroxy vitamin D level of 30 to 100 ng/mL.
– Vitamin D insufficiency is defined as a serum 25-hydroxy vitamin D level of 21 to 29 ng/mL.
– Vitamin D deficiency is defined as a serum 25-hydroxy vitamin D level of 20 ng/mL or lower.
Bouillon R, Carmeliet G. Vitamin D insufficiency: Definition, diagnosis and management. Best Pract Res Clin Endocrinol Metab. 2018 Oct;32(5):669-684. Review. PubMed PMID: 30449548.
Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM; Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30. Erratum in: J Clin Endocrinol Metab. 2011 Dec;96(12):3908. PubMed PMID: 21646368.
Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM. Guidelines for preventing and treating vitamin D deficiency and insufficiency revisited. J Clin Endocrinol Metab. 2012 Apr;97(4):1153-8. PubMed PMID: 22442274.
Sempos CT, Heijboer AC, Bikle DD, Bollerslev J, Bouillon R, Brannon PM, DeLuca HF, Jones G, Munns CF, Bilezikian JP, Giustina A, Binkley N. Vitamin D assays and the definition of hypovitaminosis D: results from the First International Conference on Controversies in Vitamin D. Br J Clin Pharmacol. 2018 Oct;84(10):2194-2207. Review. PubMed PMID: 29851137; PubMed Central PMCID: PMC6138489.
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