ObjectiveThis study was designed to evaluate the effect of high-calcium skim milk or potassium-enriched highcalcium skim milk on blood pressure compared with non-enriched skim milk.DesignThis was a randomized double-blind controlled trial. Each milk intervention lasted for 4 weeks, with a minimum of 4 weeks of wash-out between interventions.MethodsWe recruited 38 healthy people, aged over 40 years, to take part in a double-blind, randomized, controlled cross-over study. We asked them to replace their usual liquid milk with two servings per day of skim milk (control), high-calcium skim milk or potassium-enriched high-calcium skim milk. We measured office blood pressures (seated and standing) at the start and after 2 and 4 weeks of milk intervention and we measured daytime ambulatory blood pressures at the start and after 4 weeks of milk intervention. Each milk intervention was interspaced by a 4-week interval.ResultsOffice systolic blood pressure (standing) decreased from 127 ± 16 to 124 ± 16 mmHg (P< 0.05) after 4 weeks of skim milk and from 130 ± 18 to 126 ± 17 mmHg (P< 0.05) after 4 weeks of high calcium skim milk. After 4 weeks of consuming the potassium-enriched high-calcium milk, systolic blood pressure decreased from 125 ± 18 to 117 ± 16 mmHg (P< 0.001) seated, and from 130 ± 16 to 122 ± 15 mmHg (P< 0.001) standing. There were no significant changes in office diastolic blood pressure after any milk. There was no change in ambulatory blood pressure after either skim milk or high-calcium skim milk. After 4 weeks of potassium-enriched high-calcium milk, ambulatory daytime systolic blood pressure decreased from 138 ± 13 to 135 ± 11 mm Hg (P< 0.05) and daytime diastolic blood pressure decreased from 80 ± 8 to78 ± 9 mmHg (P< 0.05).ConclusionsHigh-calcium milk enriched with potassium has a small hypotensive effect in healthy people aged over 40 years.