Schleithoff 2006.

Methods	Randomised, double‐blind, placebo‐controlled trial using parallel group design (two intervention groups).
Participants	Country: Germany. Number of participants randomised: 123 patients (17% women) aged 50 to 63 (mean 51) years with congestive heart failure. Inclusion criteria: patients with congestive heart failure and New York Heart Association functional class II. Exclusion criteria: hypercalcaemia, serum creatinine concentration > 2 mg/dL, nephrolithiasis, sarcoidosis, use of a biventricular pacemaker, acute heart insufficiency, and an actual intake of supplements containing vitamin D and calcium.
Interventions	Participants were randomly assigned to receive: Intervention group 1: vitamin D3 (2000 IU) plus calcium (500 mg) daily (n = 61); Intervention group 2 (Control group): matched placebo tablet of vitamin D plus calcium 500 mg daily (n = 62); for a nine‐month period. Participants were followed‐up for a 15‐month period.
Outcomes	The primary outcome measures were survival rates, and biochemical variables such as natriuretic peptides and cytokines. Secondary outcomes were those haemodynamic variables, which were assessed routinely during the ambulatory visits, such as left ventricular ejection fraction, left ventricular end‐diastolic diameter, the cardiothoracic ratio, maximal oxygen intake (spiroergometry; O2max), and blood pressure.
Stated aim of study	"To evaluate the effect of vitamin D supplementation on the survival rate and different biochemical variables in patients with congestive heart failure."
Notes	"Compliance was measured by controlling the trial medication at each visit (bottle counts) and by the analysis of serum 25 hydroxyvitamin D concentrations." Vitamin D3 was provided by Vigantol Oel; Merck, Darmstadt, Germany, and placebo by Migliol‐Oel; Merck, Darmstadt, Germany. Additional information received thorough personal communication with Professor Armin Zittermann (10.02.2010).
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Sequence generation was achieved using computer random number generation.
Allocation concealment (selection bias)	Low risk	Allocation was controlled by a central and independent randomisation unit so that intervention allocations could not have been foreseen in advance of, or during, enrolment.
Blinding (performance bias and detection bias) All outcomes	Low risk	The trial was described as blinded, the parties that were blinded, and the method of blinding was described, so that knowledge of allocation was adequately prevented during the trial.
Incomplete outcome data (attrition bias) All outcomes	Low risk	The numbers and reasons for dropouts and withdrawals in all intervention groups were described
Selective reporting (reporting bias)	Low risk	Pre‐defined, or clinically relevant and reasonably expected outcomes are reported on.
Industry bias	Unclear risk	Vitamin D3 was provided by Vigantol Oel; Merck, Darmstadt, Germany, and placebo by Migliol‐Oel; Merck, Darmstadt, Germany.
Other bias	Low risk	The trial appears to be free of other components that could put it at risk of bias.