Study designs of evaluations included in the review
Randomised controlled trials (RCTs) were eligible for inclusion. Cluster randomised trials were excluded from the review.
Specific interventions included in the review
Studies assessing supplementation with vitamin D2 or vitamin D3, with placebo or without (open trial), were eligible for inclusion. The included studies used vitamin D supplements administered orally (on a daily, weekly or 4-monthly basis) or as a single injection. Daily doses in the included studies ranged from 300 to 2,000 IU, and study durations ranged from 6 months to 7 years. The included studies examined vitamin D, either alone or with calcium supplements. Studies that examined vitamin D analogues such as D3 (alfacalcidol) were excluded from the review.
Participants included in the review
Patients with advanced prostate cancer, chronic renal disease or end-stage renal disease, or patients undergoing renal dialysis were not eligible for inclusion. The baseline ages of participants in the included studies ranged from 33 to 106 years, with the majority being older than 60 years. The included studies used populations thatr included individuals who were classed as frail and elderly; had undergone a hip fracture operation; had past low-energy fracture; were insufficient in vitamin D; were at risk of hip fracture; or had congestive heart failure.
Outcomes assessed in the review
The primary review outcome was total mortality. However, studies were eligible for inclusion if they reported deaths from any cause separately for the intervention and control groups. Only one included study reported all-cause mortality; the majority of studies reported clinical fractures and/or bone mineral density as the main end point. Only studies that reported sufficient data to allow the estimation of relative risks (RRs) and 95% confidence intervals (CIs) were eligible for inclusion.
How were decisions on the relevance of primary studies made?
The authors did not state how the papers were selected for the review, or how many reviewers performed the selection.