(27-09-14) Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses

Vitamin D and multiple health outcomes: umbrella review of systematic reviews and meta-analyses of
observational studies and randomised trials

OPEN ACCESS
Evropi Theodoratou research fellow
1
, Ioanna Tzoulaki lecturer
2 3
, Lina Zgaga associate professor
4
,
John P A Ioannidis professor
5 6
1
Centre for Population Health Sciences, University of Edinburgh, Edinburgh EH8 9AG, UK;
2
Department of Epidemiology and Biostatistics, Imperial
College London, London W2 1PG, UK;
3
Department of Hygiene and Epidemiology, University of Ioannina School of Medicine, Ioannina 45110,
Greece;
4
Department of Public Health and Primary Care, Trinity College Dublin, Dublin 24, Ireland;
5
Stanford Prevention Research Center, Departments
of Medicine and Health Research and Policy, Stanford University School of Medicine, Stanford, CA 94305-5411, USA;
6
Department of Statistics,
Stanford University School of Humanities and Sciences, Stanford
Abstract
Objective To evaluate the breadth, validity, and presence of biases of
the associations of vitamin D with diverse outcomes.
Design Umbrella review of the evidence across systematic reviews and
meta-analyses of observational studies of plasma 25-hydroxyvitamin D
or 1,25-dihydroxyvitamin D concentrations and randomised controlled
trials of vitamin D supplementation.
Data sources Medline, Embase, and screening of citations and
references.
Eligibility criteria Three types of studies were eligible for the umbrella
review: systematic reviews and meta-analyses that examined
observational associations between circulating vitamin D concentrations
and any clinical outcome; and meta-analyses of randomised controlled
trials assessing supplementation with vitamin D or active compounds
(both established and newer compounds of vitamin D).
Results 107 systematic literature reviews and 74 meta-analyses of
observational studies of plasma vitamin D concentrations and 87
meta-analyses of randomised controlled trials of vitamin D
supplementation were identified. The relation between vitamin D and
137 outcomes has been explored, covering a wide range of skeletal,
malignant, cardiovascular, autoimmune, infectious, metabolic, and other
diseases. Ten outcomes were examined by both meta-analyses of
observational studies and meta-analyses of randomised controlled trials,
but the direction of the effect and level of statistical significance was
concordant only for birth weight (maternal vitamin D status or
supplementation). On the basis of the available evidence, an association
between vitamin D concentrations and birth weight, dental caries in
children, maternal vitamin D concentrations at term, and parathyroid
hormone concentrations in patients with chronic kidney disease requiring
dialysis is probable, but further studies and better designed trials are
needed to draw firmer conclusions. In contrast to previous reports,
evidence does not support the argument that vitamin D only
supplementation increases bone mineral density or reduces the risk of
fractures or falls in older people.
Conclusions Despite a few hundred systematic reviews and
meta-analyses, highly convincing evidence of a clear role of vitamin D
does not exist for any outcome, but associations with a selection of
outcomes are probable.



Source: BMJ 2014; 348 doi: http://dx.doi.org/10.1136/bmj.g2035 (Published 01 April 2014) Cite this as: BMJ 2014;348:g2035

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