Whether supplemental Ca has similar effects to dietary Ca on vascular and bone markers is unknown. The present trial investigated the feasibility of applying dietary and supplemental interventions in a randomised-controlled trial (RCT) aiming to estimate the effect of supplemental Ca as compared with dietary Ca on vascular and bone markers in postmenopausal women. In total, thirteen participants were randomised to a Ca supplement group (CaSuppl) (750 mg Ca from CaCO 3 + 450 mg Ca from food + 20 µg vitamin D supplement) or a Ca diet group (CaDiet) (1200 mg Ca from food + 10 µg vitamin D supplement). Participants were instructed on Ca consumption targets at baseline. Monthly telephone follow-ups were conducted to assess adherence to interventions (±20 % of target total Ca) using the multiple-pass 24-h recall method and reported pill count. Measurements of arterial stiffness, peripheral blood pressure and body composition were performed at baseline and after 6 and 12 months in all participants who completed the trial (n 9). Blood and serum biomarkers were measured at baseline and at 12 months. Both groups were compliant to trial interventions (±20 % of target total Ca intake; pill count ≥80 %). CaSuppl participants maintained a significantly lower average dietary Ca intake compared with CaDiet participants throughout the trial (453 (SD 187) mg/d v. 1241 (SD 319) mg/d; P < 0·001). There were no significant differences in selected vascular outcomes between intervention groups over time. Our pilot trial demonstrated the feasibility of conducting a large-scale RCT to estimate the differential effects of supplemental and dietary Ca on vascular and bone health markers in healthy postmenopausal women.Key words: Dietary interventions: Calcium: Arterial stiffness: Postmenopausal women Adequate intakes of Ca and vitamin D are essential for optimal bone health throughout adulthood to prevent osteoporosis and related fractures (1)(2)(3)(4)(5)(6) . Current dietary reference intakes for Ca have been established by the Institute of Medicine for women over 50 years of age -that is, the Estimated Average Requirement (EAR), RDA and Tolerable Upper Intake Level (UL) are 1000, 1200 and 2000 mg/d, respectively (7) . However, adequate intake of Ca can be difficult to achieve through dietary sources alone (8,9) .According to the National Health and Nutrition Examination Survey 2003-2006 data, less than 10 % of American women over 50 years of age reached an intake of 1200 mg/d of Ca from food alone (8) . Similarly, over 80 % of Canadian women over 50 years of age had a Ca intake <1000 mg/d from dietary sources according to the 2004 Canadian Community Health Survey (9) . Thus, to ensure adequate total Ca intake for skeletal integrity, Ca supplements are widely recommended (10,11) . Collectively, data from North America documented that 49-67 % of women aged 50-70 years and 60-65 % of those over 71 years of age reported using supplements that contain Ca (8,9) .Ca supplementation is generally well tolerated but can be associated with ...