Review of meta-analyses of non-skeletal benefits of vitamin D (Mortality, RTI, etc) – July 2017

Non-skeletal health effects of vitamin D supplementation: A systematic review on findings from meta-analyses summarizing trial data

PLOS x, July 7, 2017https://doi.org/10.1371/journal.pone.0180512
Lars Rejnmark , Lise Sofie Bislev, Kevin D. Cashman, Gudny Eiríksdottir, Martin Gaksch, Martin Grübler, Guri Grimnes, Vilmundur Gudnason, Paul Lips, Stefan Pilz, Natasja M. van Schoor, Mairead Kiely, Rolf Jorde

VitaminDWiki Summary

The Meta-analysis of Mortality and Vitamin D

The Meta-analysis of Hypertension and Vitamin D


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Background
A large number of observational studies have reported harmful effects of low 25-hydroxyvitamin D (25OHD) levels on non-skeletal outcomes. We performed a systematic quantitative review on characteristics of randomized clinical trials (RCTs) included in meta-analyses (MAs) on non-skeletal effects of vitamin D supplementation.

Methods and findings
We identified systematic reviews (SR) reporting summary data in terms of MAs of RCTs on selected non-skeletal outcomes. For each outcome, we summarized the results from available SRs and scrutinized included RCTs for a number of predefined characteristics. We identified 54 SRs including data from 210 RCTs. Most MAs as well as the individual RCTs reported null-findings on risk of cardiovascular diseases, type 2 diabetes, weight-loss, and malignant diseases.
Beneficial effects of vitamin D supplementation was reported in

  • 1 of 4 MAs on depression,
  • 2 of 9 MAs on blood pressure,
  • 3 of 7 MAs on respiratory tract infections, and
  • 8 of 12 MAs on mortality.

Most RCTs have primarily been performed to determine skeletal outcomes, whereas non-skeletal effects have been assessed as secondary outcomes.
Only one-third of the RCTs had low level of 25OHD as a criterion for inclusion and a mean baseline 25OHD level below 50 nmol/L was only present in less than half of the analyses.

Conclusions
Published RCTs have mostly been performed in populations without low 25OHD levels. The fact that most MAs on results from RCTs did not show a beneficial effect does not disprove the hypothesis suggested by observational findings on adverse health outcomes of low 25OHD levels.

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