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PLoS One. 2017 Jul 7;12(7):e0180512. doi: 10.1371/journal.pone.0180512. eCollection 2017.

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

Author information

1
Department of Endocrinology and Internal Medicine, Aarhus University Hospital, Aarhus, Denmark.
2
Cork Centre for Vitamin D and Nutrition Research, School of Food and Nutritional Sciences, University College Cork, Cork, Ireland.
3
Icelandic Heart Association, Kopavogur, Iceland.
4
Division of Endocrinology and Diabetology, Department of Internal Medicine, Medical University of Graz, Graz, Austria.
5
Swiss Cardiovascular Centre Bern, Department of Cardiology, Inselspital, Bern University Hospital, University of Bern, Bern, Switzerland.
6
Tromsø Endocrine Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway.
7
Faculty of Medicine, School of Health Sciences, University of Iceland, Reykjavik, Iceland.
8
Department of Internal Medicine, Section of Endocrinology, Vrije University Medical Center, Amsterdam, Netherlands.
9
Amsterdam Public Health Research Institute, Department of Epidemiology and Biostatistics, VU University Medical Center, Amsterdam, Netherlands.

Abstract

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.

PMID:
28686645
PMCID:
PMC5501555
DOI:
10.1371/journal.pone.0180512
[Indexed for MEDLINE]
Free PMC Article

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