Letters Vitamin D deficiency

Position statements on vitamin D deficiency are no substitute for well designed studies

BMJ 2013; 346 doi: http://dx.doi.org/10.1136/bmj.f956 (Published 19 February 2013) Cite this as: BMJ 2013;346:f956
  1. Stephen S Nussey, professor of endocrinology1
  1. 1St George’s Hospital Medical School, London SW17 0RE, UK
  1. s.nussey{at}stgeorges.nhs.uk

The recent statement by the British Paediatric and Adolescent Bone Group causes concern in an era that demands objectivity.1 Where is the evidence for the statements made? Which criteria are the definition of vitamin D deficiency based on? None is stated.

Why is a cut-off point of 25 nmol/L (1 nmol/L=0.4 ng/mL) for serum 25-hydroxyvitamin D3 (25-(OH)D3) concentration used? No reason is given. This value is much lower than that used by other expert bodies, including paediatric societies.2 Autopsy data (albeit from an adult population) showed increased osteoid volumes (marker of osteomalacia) in half of those with 25-(OH)D3 concentrations of 50-75 nmol/L.3 The statement provides no evidence that children are any different.1

The association between rickets and fractures is problematic. Most infants with rickets have no evident fractures (but skeletal surveys are not routinely done). The extent to which vitamin D deficiency increases bone fragility is not known; nor do we know why a minority of children with rickets have a fracture and a few have several. Postmortem studies in the first decade of the 20th century showed that rickets has clear histopathological findings and is ultimately a histopathological entity.4 Medical Research Council studies in post-war Vienna showed that histological rickets could precede radiological change “by up to several weeks.”5 It is also well known that the clinical, radiological, biochemical, and histological features of rickets correlate poorly.6 Thus, it is not clear on what evidence the group can categorically exclude vitamin D as a causal factor in fracture because other features have yet to develop. Indeed, “it is too dogmatic to suggest that subclinical rickets does not exist.”4

Some infants with vitamin D deficiency may be abused and have fractures, but suspected cases must be analysed and judged on an individual basis, with all aspects examined objectively and in detail. Appropriate vitamin D supplementation of all pregnant and lactating women and children would help to remove vitamin D deficiency as a potential confounding factor. The US Institute of Medicine increased its recommended doses in 2011.2 Importantly, the statement does not cover the important question of whether current UK recommended doses of vitamin D raise serum vitamin D concentrations adequately.

The lack of well designed studies should prompt a call for such studies to be carried out. Or are citations of support from committees to be a substitute for citations of referenced material?

Notes

Cite this as: BMJ 2013;346:f956

Footnotes

  • Competing interests: SSN takes 25 µg vitamin D3 daily and has acted as an expert witness in cases of vitamin D deficiency.

References