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

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          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.

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          Most cited references85

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          The role of vitamin D and calcium in type 2 diabetes. A systematic review and meta-analysis.

          Altered vitamin D and calcium homeostasis may play a role in the development of type 2 diabetes mellitus (type 2 DM). EVIDENCE ACQUISITION AND ANALYSES: MEDLINE review was conducted through January 2007 for observational studies and clinical trials in adults with outcomes related to glucose homeostasis. When data were available to combine, meta-analyses were performed, and summary odds ratios (OR) are presented. Observational studies show a relatively consistent association between low vitamin D status, calcium or dairy intake, and prevalent type 2 DM or metabolic syndrome [OR (95% confidence interval): type 2 DM prevalence, 0.36 (0.16-0.80) among nonblacks for highest vs. lowest 25-hydroxyvitamin D; metabolic syndrome prevalence, 0.71 (0.57-0.89) for highest vs. lowest dairy intake]. There are also inverse associations with incident type 2 DM or metabolic syndrome [OR (95% confidence interval): type 2 DM incidence, 0.82 (0.72-0.93) for highest vs. lowest combined vitamin D and calcium intake; 0.86 (0.79-0.93) for highest vs. lowest dairy intake]. Evidence from trials with vitamin D and/or calcium supplementation suggests that combined vitamin D and calcium supplementation may have a role in the prevention of type 2 DM only in populations at high risk (i.e. glucose intolerance). The available evidence is limited because most observational studies are cross-sectional and did not adjust for important confounders, whereas intervention studies were short in duration, included few subjects, used a variety of formulations of vitamin D and calcium, or did post hoc analyses. Vitamin D and calcium insufficiency may negatively influence glycemia, whereas combined supplementation with both nutrients may be beneficial in optimizing glucose metabolism.
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            25-hydroxyvitamin D and risk of myocardial infarction in men: a prospective study.

            Vitamin D deficiency may be involved in the development of atherosclerosis and coronary heart disease in humans. We assessed prospectively whether plasma 25-hydroxyvitamin D (25[OH]D) concentrations are associated with risk of coronary heart disease. A nested case-control study was conducted in 18,225 men in the Health Professionals Follow-up Study; the men were aged 40 to 75 years and were free of diagnosed cardiovascular disease at blood collection. The blood samples were returned between April 1, 1993, and November 30, 1999; 99% were received between April 1, 1993, and November 30, 1995. During 10 years of follow-up, 454 men developed nonfatal myocardial infarction or fatal coronary heart disease. Using risk set sampling, controls (n = 900) were selected in a 2:1 ratio and matched for age, date of blood collection, and smoking status. After adjustment for matched variables, men deficient in 25(OH)D ( or=30 ng/mL) (relative risk [RR], 2.42; 95% confidence interval [CI], 1.53-3.84; P < .001 for trend). After additional adjustment for family history of myocardial infarction, body mass index, alcohol consumption, physical activity, history of diabetes mellitus and hypertension, ethnicity, region, marine omega-3 intake, low- and high-density lipoprotein cholesterol levels, and triglyceride levels, this relationship remained significant (RR, 2.09; 95% CI, 1.24-3.54; P = .02 for trend). Even men with intermediate 25(OH)D levels were at elevated risk relative to those with sufficient 25(OH)D levels (22.6-29.9 ng/mL: RR, 1.60 [95% CI, 1.10-2.32]; and 15.0-22.5 ng/mL: RR, 1.43 [95% CI, 0.96-2.13], respectively). Low levels of 25(OH)D are associated with higher risk of myocardial infarction in a graded manner, even after controlling for factors known to be associated with coronary artery disease.
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              Sifting the evidence-what's wrong with significance tests?

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                Author and article information

                Contributors
                Role: research fellow
                Role: lecturer
                Role: associate professor
                Role: professor
                Journal
                BMJ
                BMJ
                bmj
                BMJ : British Medical Journal
                BMJ Publishing Group Ltd.
                0959-8138
                1756-1833
                2014
                1 April 2014
                : 348
                : g2035
                Affiliations
                [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
                Author notes
                Correspondence to: E Theodoratou  e.theodoratou@ 123456ed.ac.uk
                Article
                thee017309
                10.1136/bmj.g2035
                3972415
                24690624
                eb0b5da8-45a2-4ece-b707-e9ccd58131f0
                © Theodoratou et al 2014

                This is an Open Access article distributed in accordance with the Creative Commons Attribution Non Commercial (CC BY-NC 3.0) license, which permits others to distribute, remix, adapt, build upon this work non-commercially, and license their derivative works on different terms, provided the original work is properly cited and the use is non-commercial. See: http://creativecommons.org/licenses/by-nc/3.0/.

                History
                : 24 February 2014
                Categories
                Research

                Medicine
                Medicine

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