ISRCTN17873085.

Trial name or title	The impact of vitamin D supplementation in chronic heart failure
Methods	Randomised, double‐blind, placebo‐controlled trial using parallel group design (2 intervention groups)
Participants	Country: United Kingdom Estimated number of participants: 100 Inclusion criteria: participants aged 18 years or over with class II and III heart failure due to left ventricular systolic dysfunction (left ventricular ejection fraction ≤ 40%); stable symptoms for 3 months on maximally tolerated medical therapy with no recent change in medication; able to give informed written consent Exclusion criteria: currently taking (or have taken in the previous 3 months) calcium or other vitamin supplements; currently prescribed amlodipine or other calcium channel antagonists (intake of spironolactone will be recorded); chronic heart failure due to untreated valvular heart disease; history of primary hyperparathyroidism, sarcoidosis, tuberculosis or lymphoma; vitamin D levels greater than 50 nmol/L
Interventions	Participants will be randomly assigned to receive: Intervention group: vitamin D₃ (4000 IU) daily Comparator group: placebo daily for a period of 1 year
Outcomes	The primary outcome measure will be: left ventricular function assessed at baseline and 12 months, measured by cardiac magnetic resonance. Secondary outcome measures will be: symptom status (New York Heart Association status), measured at baseline, 1, 4, 8, 12 months; exercise tolerance, measured at baseline and 12 months; quality of life (Minnesota living with heart failure questionnaire, European Quality of Life instrument and a 19‐item Likert scale index), measured at baseline, 1, 4, 8, 12 months; flow mediated dilatation, measured at baseline and 12 months; immune status, measured at baseline and 12 months; insulin resistance, measured at baseline and 12 months; autonomic activation (measured by heart rate variability), measured at baseline and 12 months; renal function, measured at baseline, 1, 4, 8, and 12 months; B‐type natriuretic peptide, measured at baseline, 1, 4, 8, and 12 months
Starting date	January 2009; expected completion December 2012
Contact information	Klaus Witte Division of Cardiovascular and Diabetes Research LIGHT building University of Leeds, Leeds, United Kingdom, LS2 9JT klauswitte@hotmail.com
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