Re: Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of observational studies and randomised trials
The big problem with randomised trials of vitamin D supplementation is that woefully inadequate doses of vitamin D are used (e.g. 800 IU per day). Whilst the optimal blood level of (25-hydroxy) vitamin D is still a matter of debate, 100-200 nmol/L might be the ideal; the daily dose of vitamin D3 required to achieve this in adults is typically 5,000-10,000 IU per day (such doses are quite safe, as potential toxicity appears to require a sustained dose of 40,000 IU per day, and blood levels in excess of 375 nmol/L). It is thus hardly surprising when significant results are not seen – how many pharmaceutical drug trials would show a positive result if the drug being tested was given in an amount of only one-tenth of the therapeutic dose?!
Competing interests: No competing interests