Understanding Why Vitamin D Deficiency is Not So Common Afterall

An excellent commentary (JE Marrison et al. NEJM 2016; 375: 1817-20) throws a bunch of cold water on the idea that there is a massive vitamin D deficiency pandemic.  The main contention of the authors is that physicians, and by extension patients, focus too closely at specific thresholds which are poorly understood.

They explain the term “Estimated Average Requirement” (EAR) which is the median of the distribution of human requirements.  Whereas, the RDA or recommended daily allowance “reflects the estimated requirement for people at the highest end of the distribution.”  So, at least 97.5% of people will have a requirement below the RDA.  However, due to Vitamin D’s importance, particularly with bone health, “the EAR is set at 400 IU per day for persons 1 to 70 years of age and 600 IU per day for persons older than 70.”

Other key points:

  • The EAR and RDA assume minimal to no sun exposure.
  • The RDAs of 600 IU/day and 800 IU/day correspond to 25(OH)D level of  16 ng/mlL and 20 ng/mL.
  • “A common misconception is that the RDA functions as a ‘cut point’ and that the entire population must have a serum 25(OH)D level above 20 ng per millimeter to achieve good bone health.”
  • “Approximately half the population has a requirement of 16 ng per milliliter (the EAR) or less.”
  • “Many studes establish ‘inadequacy’ using the RDA, though it is actually at the upper end of the spectrum of human need.” Thus, most people who are labelled as deficient are misclassified.
  • Using correct methodology, the authors assert that 13% of Americans 1-70 years are ‘at risk’ and <6% are deficient (with 25(OH)D < 12.5 ng/mL.

The problem with excessive Vitamin D testing and excessive treatment:

  • If 97.5% of the population has levels of Vitamin D exceeding 20 ng/mL, there are likely to be adverse effects in addition to increased costs of testing/treating.

Who to screen?

  • Those with risk factors for vitamin D deficiency: osteoporosis, osteomalacia, malabsorption, medications that can affect vitamin D metabolism (eg. anticonvulsants), or institutionalization
  • “For healthy patients, routine screening is not recommended by most medical organizations.” Though, the authors do recommend that “the RDA will nearly always meet the needs of generally healthy people.”

My take: This article makes a good argument for less testing along with avoidance of overprescribing vitamin D.  Nevertheless, for healthy people taking the RDA for vitamin D is quite sensible.

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Disclaimer: These blog posts are for educational purposes only. Specific dosing of medications/diets (along with potential adverse effects) should be confirmed by prescribing physician/nutritionist.  This content is not a substitute for medical advice, diagnosis or treatment provided by a qualified healthcare provider. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a condition.

Victoria Chimes -Maine's Ship on their state quarter

Victoria Chimes -Maine’s Ship on their state quarter

5 thoughts on “Understanding Why Vitamin D Deficiency is Not So Common Afterall

  1. I thought the Institute of medicine set the level of deficiency at 20. What about all the articles that have worse risks or outcomes for levels of vitamin D under 20?

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