Salt restriction among hypertensive patients: Modest blood pressure effect and no adverse effects

OBJECTIVE: Previous studies, mainly evaluating short-term very low salt diets, suggest that salt restriction may influence glucose and insulin metabolism, catecholamines, renin, aldosterone, and lipid levels adversely. The authors wanted to explore whether sodium restriction for eight weeks influenced insulin secretion unfavourably, and evaluate the efficacy and safety of such treatment also in terms of other parameters important in the management of hypertensive patients. DESIGN: A double-blind randomized controlled parallel group designed trial. All participants received dietary advice aimed at a moderate salt-restricted diet. Half of the participants received salt capsules, the others received identical placebo capsules. SETTING: General practice. SUBJECTS: Forty-six hypertensive patients inadequately controlled by drug treatment. MAIN OUTCOME MEASURES: Fasting serum insulin C-peptide and glucose and levels of these measures after oral glucose, blood pressure, serum aldosterone and lipids, peripheral resistance, and skin conductance. RESULTS: Salt restriction did not influence glucose and insulin metabolism, aldosterone, or lipid levels adversely. We observed better blood pressure regulation in the low salt group than in the high salt group, with a systolic and diastolic blood pressure difference of 5/5 mmHg after eight weeks. The difference was only statistically significant for diastolic blood pressure, p 0.02. CONCLUSION: This study revealed a modest diastolic blood pressure reducing effect of moderate sodium restriction. This reduction was obtained without any apparent unfavourable side effects such as increased insulin secretion, impaired glucose tolerance or dyslipidaemia.