In 200 patients with documented systolic heart failure give supplementation with vitamin D in those with a 25-OH- vitamin D < 50nmol/L - or placebo.

In those with a vitamin D level <25nmol/L a substitution of 2400IU will be given, and in those with a vitamin D level 25-50nmol/L a substitution of 1600IU will be given.

Intervention time 12 months. Biomarkers of heart function, quality of life, and hospitalisation will be analysed.

In a population with a systolic heart failure with an EF<40%, the levels of vitamin D will be analysed. In those with a 25-OH-vitamin D level <50nmol/L the patients that accept participation, will be randomised into active supplementation as described below, or placebo.

• In those with a 25-OH-vitamin D level <25nmol/L there will be a supplementation of 2400IU daily
• In those with a vitamin D level 25-50nmol/L there will be a supplementation of 1600IU daily,
• or placebo. Thus based on the basal level of vitamin D the screened patients will either be excluded due to high level of vitamin D, or given one ot the two options of vitamin D dosage based on the basal patient level - or placebo.

The intervention time will be 12 months. In the project 200 heart failure patients will be included. Blood samples including heart failure biomarkers, and biomarkers for inflammation and oxidative stress will be drawn at 3,6, 9 and 12 months.

Health related quality of life will be evaluated by use of Euro-QoL-5D Minnesota Living with Heart Failure.Patient Health Questionnaire-9 Multidimensional Fatigue Inventory 20 questionnaire, as also hospitalisation during the project time.

Cardiac function according to echocardiography will be analysed at start, and study end.

Inclusion Criteria:

• Patients with documented and stable systolic heart failure and connected to an outpatient clinic at the Dept of Cardiology in Linköping, or Jönköping, Sweden, and with a 25-OH-vitamin D <50nmol/L

Exclusion Criteria:

• Patients with unstable heart failure
• Patients with significant valvular disease, or ischemic heart disease planned for operation
• Patients with significant renal or /and liver impairment.
• Patients that do not understand that study information, or that are not willing to participate

Neither the participant, nor the care provider will be informed if active supplementation or placebo will be given, nor will blood sample results be open for care provider