['Red cell distribution width (RDW) is associated with increased risk of heart failure (HF). We examined in a healthy population (1) whether this association is independent of cardiovascular risk factors and iron metabolism and (2) whether RDW associates with physical activity.', 'Hazard ratios (HRs, highest quartile versus lowest quartile of RDW) for the risk of HF were calculated in 17,533 participants from the European Prospective Investigation into Cancer and Nutrition (EPIC)-Norfolk cohort. During a follow-up of 11.2±2.2 years 640 participants developed a HF event. The HR for HF events was 1.44 (95%CI 1.15-1.80, p<0.001). There was a non-linear increase in HF risk across RDW quartiles. Adjustment for established risk factors (sex, age, diabetes, smoking, systolic blood pressure, total and high-density lipoprotein cholesterol) attenuated the HR for HF to 1.40 (95%CI 1.11-1.77, p=0.001). Adjustment for CRP, iron and ferritin levels did not affect the HR for HF. RDW levels are inversely associated with physical activity (per category β=-0.37, 95%CI -0.053 to -0.021, p<0.0001), independent of iron metabolism. However, the association between HF and RDW levels was not changed by physical activity.'] Is red cell distribution width associated with physical inactivity and heart failure , independent of established risk factors , inflammation or iron metabolism ; the EPIC-Norfolk study?