Calcium supplements and 24-hour blood pressure

INTERVENTION: 0.5 grams of calcium as the citrate salt to be taken twice a day (once in the morning and once in the evening, 12 hours apart). The morning dose will taken at our clinic with a standardized breakfast meal consisting of toast with spread, fruit and tea or coffee. The evening dose will be taken by participants at home. The intervention will be administered as oral tablets. The intervention will be taken by all participants at the first or second visit (in a cross‐over design) with at least a 7 day washout period between visits. Those that receive the intervention at the second visit will continue to receive the intervention for a further 4 weeks. Adherence to the intervention will be monitored by tablet return. CONDITION: Blood pressure Osteoporosis PRIMARY OUTCOME: Difference in the change from baseline in diastolic blood pressure between day one of calcium supplementation and day one of placebo Difference in the change from baseline in systolic blood pressure between day 1 of calcium supplementation and day 1 of placebo SECONDARY OUTCOME: Difference in the change from baseline in diastolic blood pressure between day 1 of calcium or placebo supplementation and after 4 weeks of continuous supplementation Difference in the change from baseline in systolic blood pressure between day 1 of calcium or placebo supplementation and after 4 weeks of continuous supplementation INCLUSION CRITERIA: Female At least 5‐years postmenopause Age >55 years if age at menopause unknown