ESPE Yearbook of Paediatric Endocrinology

To read the full abstract: JAMA. 2019 Aug 27;322(8):736–745. doi: 10.1001/jama.2019.11889

Two legs good, four legs better? Vitamin D supplementation is widely recommended in various national guidelines at doses of 400 to 2000 iu per day in children and adults for its benefits on bone health. So you might think that more would be even better? At least 3% of US adults agree with this extrapolation and report intakes of 4000 iu per day or more.

These authors tested this question in a 3-year long, double-blind, randomized clinical trial in Calgary, Canada, on 311 healthy adults without osteoporosis, aged 55–70 years. Surprisingly, age-related reduction in bone mineral density was lowest in the recommended vitamin D dose group (400 IU/day group: −1.2% at the radius) and was progressively worse on the higher (4000 IU/day: −2.4%) and highest doses (10 000 IU/day: −3.5%). The authors should be congratulated in admitting that the clearly significant findings of this well-designed trial were in the opposite direction of their research hypothesis. This is a reminder of the principle that the design of any scientific work must include the option to reject the hypothesis.

The findings present an important lesson against extrapolating from established to higher doses, and they also provide a timely warning against the ‘pre-cautionary’ use of high dose vitamin D for protection against a myriad of putative, but unproven benefits – including appropriate scientific evaluation of its use in the prevention or treatment of COVID-19 infection (1).

Reference:

1. National Institute for Health and Care Excellence. COVID-19 rapid evidence summary: vitamin D for COVID-19. Published date: 29 June 2020 https://www.nice.org.uk/advice/es28/chapter/Key-messages