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Vitamin D "insufficiency" in adults: beware of vague concepts with uncertain clinical relevance

FEATURED REVIEW There is no proof that measuring blood levels of vitamin D in the general population or in selected subgroups leads to an improvement in the health of those concerned.
Full review (4 pages) available for download by subscribers.

Abstract

  • According to certain "reference ranges", about a billion people worldwide, including 80% of the French population, have vitamin D insufficiency or deficiency.
     
  • In France, serum vitamin D assay has become commonplace. Between 2010 and 2011, the number of tests performed increased by about 70%, the most rapid growth in any laboratory assay.
     
  • How are "normal" vitamin D levels and, thus, vitamin D insufficiency or deficiency, established, and what is their clinical relevance? To answer these questions, we reviewed the literature using the standard Prescrire methodology.
     
  • In early 2013, there is no international consensus on normal serum concentrations of
    25-hydroxyvitamin D (25(OH)D).
     
  • Using biochemical criteria, some experts define normal vitamin D status as a blood 25(OH)D concentration above 30 ng/ml and vitamin D insufficiency as levels between 20 and 30 ng/ml.
     
  • The definition of vitamin D insufficiency is disputed by other experts, who point out that 97.5% of the general population with vitamin D levels of at least 20 ng/ml have no bone disorders.
     
  • Biostatistical data suggest that the normal range of 25(OH)D levels is between 11 and 46 ng/ml, but the lower limit appears to vary according to the study population.
     
  • Epidemiological data have shown a link between 25(OH)D concentrations below 20 ng/ml and a variety of clinical disorders, including osteoporosis, fractures, cancer, infections, and autoimmune diseases. Although these data suggest a possible increase in the risk of particular disorders, they provide no information on the harm-benefit balance of vitamin D supplementation.
     
  • A few clinical trials have shown that combined calcium and vitamin D supplementation (but not vitamin D alone) has a modest preventive effect on osteoporotic fractures in some subgroups of persons over 65 years old. Some trials showed that the calcium plus vitamin D combination was more effective than calcium alone or placebo in reducing falls among some elderly subgroups. Elderly patients were recruited for most of these trials regardless of their vitamin D status.
     
  • Vitamin D supplementation carries a risk, albeit very small, of vitamin D overdose and hypercalcaemia. Vitamin D plus calcium supplementation increases the risk of kidney stones.
     
  • In practice, when treatment with vitamin D is envisaged, there is no need to determine vitamin D status by conducting blood tests. In contrast, monitoring calcium levels can help prevent overdose. 

©Prescrire 1 October 2013

"Vitamin D "insufficiency" in adults. Beware of vague concepts with uncertain clinical relevance" Prescrire Int 2013; 22 (142): 245-248. (Pdf, subscribers only)
Download the full review.
Pdf, subscribers only