Witham 2010.

Methods	Randomised, double‐blind, placebo‐controlled trial using parallel group design (two intervention groups).
Participants	Country: United Kingdom. Number of participants randomised: 105 patients with systolic heart failure aged 70 or over (mean 79.7) years, 34% females with 25‐hydroxyvitamin D levels < 50nmol/L (20 ng/ml). Inclusion criteria: aged 70 years or over with a previously recorded clinical diagnosis of chronic heart failure, previously documented left ventricular systolic dysfunction by echocardiography, radionuclide ventriculography or angiography as part of their usual clinical care, a New York Heart Association class II or III symptoms, and a 25‐hydroxyvitamin D level of < 50nmol/L (20 ng/ml). Exclusion criteria: a clinical diagnosis of osteomalacia, under investigation for recurrent falls, already taking vitamin D supplements, moderate to severe cognitive impairment, defined as a Folstein mini‐mental state examination < 15/30), serum creatinine > 200umol/L, liver function tests (bilirubin, alanine aminotransferase, alkaline phosphatase) > 3 times the upper limit of the local reference range, systolic blood pressure < 90mmHg, albumin adjusted calcium > 2.55 mmol/L or < 2.20 mmol/L), metastatic malignancy, and wheelchair bound patients unable to perform the primary outcome, and excluded patients unwilling or unable to give informed consent.
Interventions	Participants were randomly assigned to receive: Intervention group 1: vitamin D2 (10,000 IU) tablet at baseline and 10 weeks (n = 53); Intervention group 2 (Control group): matched placebo tablet at baseline and 10 weeks (n = 52). Participants were followed for 20 weeks.
Outcomes	The primary outcome measure was the six‐minute walk test, a measure of submaximal exercise capacity. Secondary outcomes were muscle function, daily physical activity levels, health status/health‐related quality of life, cardiovascular and inflammatory markers.
Stated aim of study	"To examine whether vitamin D supplementation could improve parameters that are directly relevant to older people with heart failure – i.e., exercise capacity, physical function and quality of life."
Notes	"Administration of vitamin D2 was supervised in the participant’s own home by the research nurse to ensure 100% adherence."
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Randomisation was performed using computer generated random number tables by DHP Pharmaceuticals (Gwent, UK).
Allocation concealment (selection bias)	Low risk	Allocation was controlled by a central and independent randomisation unit. Code allocation was concealed from the research nurse and investigators until after data analysis was complete.
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. DHP Pharmaceuticals (Gwent, UK) encapsulated the trial medication to render it identical to placebo.
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	Low risk	The trial is not funded by a manufacturer of vitamin D.
Other bias	Low risk	The trial appears to be free of other components that could put it at risk of bias.