Sodium restriction and blood pressure in hypertensive type II diabetics: Randomised blind controlled and crossover studies of moderate sodium restriction and sodium supplementation

Abstract

Objective - To determine the effect of moderate dietary sodium restriction on the hypertension of non-insulin-dependent (type II) diabetes. Design - Randomised parallel controlled study of moderate sodium restriction for three months compared with usual diabetic diet, followed by randomised double blind crossover trial of sustained release preparation of sodium for one month versus placebo for one month in patients continuing with sodium restriction. Setting - Patients attending diabetic outpatient clinic of city hospital. Patients - Thirty four patients with established type II diabetes complicated by mild hypertension (systolic blood pressure >160 mm Hg or diastolic pressure >95 mm Hg on three consecutive occasions). Patients already taking antihypertensive agents (but not diuretics) not barred from study provided that criteria for mild hypertension still met. Conditions precluding patients from study were diabetic or hypertensive nephropathy, cardiac failure, and pregnancy. Interventions - After run in phase with recordings at seven weeks, three weeks, an time zero patients were allocated at random to receive moderate dietary sodium restriction for three months (n = 17) or to continue with usual diabetic diet. Subsequently nine patients in sodium restriction group continued with regimen or a further two months, during with they completed a randomised double blind crossover trial of sustained release preparation of sodium (Slow Sodium 80 mmol daily) for one month versus matching placebo for one month. End point - Reduction in blood pressure in type II diabetics with mild hypertension. Measurements and main results - Supine and erect blood pressure, body weight, and 24 hour urinary sodium and potassium excretion measured monthly during parallel group and double blind crossover studies. After parallel group study sodium restriction group showed significant reduction in systolic blood pressure (supine 19.2 mm Hg, erect 21.4 mm Hg; p < 0.001) and mean daily urinary sodium excretion (mean reduction 60 mmol/24 h). There were no appreciable changes in weight, diabetic control, or diastolic pressure. No significant changes occurred in controls. In double blind crossover study mean supine systolic blood pressure rose significantly (p < 0.005) during sodium supplementation (to 171 mm Hg) compared with value after three months of sodium restriction alone (159.9 mm Hg) and after one month of placebo (161.8 mm Hg). Conclusions - Moderate dietary restriction of sodium has a definite hypotensive effect, which may be useful in mild hypertension of type II diabetes.