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#106 Vitamin D Levels: Vitamin Do or Vitamin Don’t


CLINICAL QUESTION
QUESTION CLINIQUE
 In adults, what is the evidence to test serum vitamin D levels?

BOTTOM LINE
RÉSULTAT FINAL
 Routine testing of vitamin D levels is unnecessary.  Laboratories often report serum levels between 50 and 75–80 nmol/L as insufficient but this is not supported by consistent or reliable evidence. Additionally, large variability in the test limits interpretation of repeat measurements.  


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EVIDENCE
DONNÉES PROBANTES
 Target serum level: 
  • An extensive systematic review1 on serum 25-hydroxyvitamin D (25-OHD) suggests levels: 
    • >75 nmol/L “are not consistently associated with increased benefit.” 
    • Above 50 nmol/L are “practically sufficient for all persons.”    
    • Between 30–50 nmol/L “places some, but not all, persons at risk for inadequacy.” 
    • <30 nmol/L places one “at risk relative to bone health.”   
No randomized controlled trials in falls or fractures have investigated treating specific vitamin D level targets.   Proportion of population with various levels: 
  • Levels <75–80 nmol/L for Canada, USA, and UK are 97%, 77%, and 87%, respectively.2-4 These are not necessarily concerning based on above systematic review. 
  • Canadian results of potentially concerning levels showed 61% are <50 nmol/L2 and 13% below 40 nmol/L.1 
  Context: 
  • While levels ≤74 nmol/L are considered “insufficient” by some provincial laboratories,5 this is not supported by the evidence. 
  • Every 800 IU of vitamin D increases 25-OHD by 8–16 nmol/L; however, the dose-response relationship is not directly linear and is affected by many factors such as season, adiposity, and skin pigmentation.1,6 
  • Vitamin D assays have a coefficient of variation that may be as high as 10–20%,1 meaning changes in levels with doses of 800 IU/day may not be discernable due to variability in the test.  
  • TOP guidelines suggest supplementing without testing and exceptions where testing may be helpful are also provided in these guidelines.7   
  • Mega doses of vitamin D (i.e. 150,000 IU every three months) have been associated with increased adverse events, including falls and fractures.8,9  
  • Enrolment in many vitamin D supplementation trials was not based on vitamin D levels and treating on speculation was beneficial.10-12 
  • Vitamin D doses in most trials were not adjusted based on vitamin D levels.13-19 
  • A 25-OHD assay costs $61.32.20 

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Author(s)
Auteur(s)
  • Adrienne J Lindblad BSP ACPR PharmD
  • James McCormack BSc(Pharm) PharmD
  • Scott Garrison MD PhD

1. IOM (Institute of Medicine). 2011. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press.

2. Rucker D, Allan JA, Fick GH, et al. CMAJ. 2002; 166(12):1517–24.

3. Hyppönen E, Power C. Am J Clin Nutr. 2007; 85:860–8.

4. Ginde AA, Liu MC, Camargo CAJ. Arch Intern Med. 2009; 169(6):626–32.

5. BC Biomedical Laboratories Adult Reference Ranges. Available at: http://198.71.215.83/refranges/Laboratory%20Adult%20Reference%20Intervals.pdf. Last accessed November 18, 2013.

6. Moyad M. Dermatol Nurs. 2009; 21(1):25–30,55.

7. Toward Optimized Practice. Vitamin D Guideline. Available at: http://www.topalbertadoctors.org/cpgs/28048723. Last accessed November 18, 2013.

8. Sanders KM, Stuart AC, Williamson EJ, et al. JAMA. 2010; 303(18):1815–22.

9. Glendenning P, Zhu K, Indjerjeeth C, et al. J Bone Miner Res. 2012; 27(1):170–6.

10. Bischoff-Ferrari HA, Willett WC, Wong JB, et al. Arch Intern Med. 2009; 169(6):551–61.

11. Bischoff-Ferrari HA, Dawson-Hughes B, Willett WC, et al. JAMA. 2004; 291(16):1999–2006.

12. Autier P, Gandini S. Arch Intern Med. 2007; 167(16):1730–7.

13. Chapuy MC, Arlot ME, Duboeuf F, et al. N Engl J Med. 1992; 327(23):1637–42.

14. Meyer HE, Smedshaug GB, Kvaavik E, et al. J Bone Miner Res. 2002; 17(4):709–15.

15. Trivedi DP, Doll R, Khaw KT. BMJ. 2003; 326(7387):469–72.

16. Lips P, Graafmans WC, Ooms ME, et al. Ann Intern Med. 1996; 124(4):400–6.

17. Grant AM, Avenell A, Campbell MK, et al. Lancet. 2005; 365(9471):1621–8.

18. Porthouse J, Cockayne S, King C, et al. BMJ. 2005; 330(7498):1003.

19. Jackson RD, LaCroix AZ, Gass M, et al. N Engl J Med. 2006; 354(7):669–83.

20. British Columbia Medical Association. Vitamin D Testing Protocol. Available at: http://www.bcguidelines.ca/pdf/vitamind.pdf. Last accessed November 18, 2013.

21. Allan GM, Korownyk C. Tools for Practice. Available at: http://www.acfp.ca/Portals/0/docs/TFP/20131212_021925.pdf. Last accessed January 21, 2014.

Authors do not have any conflicts of interest to declare.

Les auteurs n’ont aucun conflit d’intérêts à déclarer.