Increased potassium intake from fruit and vegetables or supplements does not lower blood pressure or improve vascular function in UK men and women with early hypertension: a randomised controlled trial

K-rich fruit and vegetables may lower blood pressure (BP) and improve vascular function. A randomised controlled trial (ISRCTN50011192) with a cross-over design was conducted in free-living participants with early stages of hypertension (diastolic BP > 80 and < 100 mmHg, not receiving BP-lowering medication) to test this hypothesis. Following a 3-week run-in period on a control diet, each subject completed four dietary 6-week dietary interventions (control + placebo capsules, an additional 20 or 40 mmol K+/d from fruit and vegetables or 40 mmol potassium citrate capsules/d) using a Latin square design with a washout period >= 5 weeks between the treatment periods. Out of fifty-seven subjects who were randomised, twenty-three male and twenty-five female participants completed the study; compliance to the intervention was corroborated by food intake records and increased urinary K+ excretion; plasma lipids, vitamin C, folate and homocysteine concentrations, urinary Na excretion, and body weight remained were unchanged. On the control diet, mean ambulatory 24 h systolic/diastolic BP were 132.3 (SD 12.0)/81.9 (SD 7.9) mmHg, and changes (Bonferroni's adjusted 95% CI) compared with the control on the diets providing 20 and 40 mmol K+/d as fruit and vegetables were 0.8 (-3.5, 5.3)/0.8 (-1.9, 3.5) and 1.7 (-3.0, 5.3)/1.5 (-1.5, 4.4), respectively, and were 1.8 (-2.1, 5.8)/1.4 (-1.6, 4.4) mmHg on the 40 mmol potassium citrate supplement, and were not statistically significant. Arterial stiffness, endothelial function, and urinary and plasma isoprostane and C-reactive protein (CRP) concentrations did not differ significantly between the diets. The present study provides no evidence to support dietary advice to increase K intake above usual UK intakes in the subjects with early stages of hypertension.