Metabolic effects of strict salt restriction in essential hypertensive patients

OBJECTIVE: Some observations suggest that a strict low-salt diet may induce unfavourable metabolic side-effects. The main aim of this study was to analyse the possible consequences of severe salt restriction in mildly hypertensive patients. DESIGN: The study was carried out through a randomized double-blind protocol. SUBJECTS: Forty-seven ambulatory patients proceeding from the hypertension unit were initially admitted: 17 were lost, and 30 non-diabetic mildly hypertensives (DBP 90-104 mmHg) with normal renal function completed the protocol. INTERVENTION: After a wash-out period, patients were maintained on a low-salt intake (2.8 +/- 1.0 g day-1 of NaCl) and placebo for 2 weeks, and the same diet and salt supplements (11.7 +/- 2.5 g day-1 of NaCl) for another 2 weeks, separated by a second wash-out period. MEASURES: At the end of each dietary period, blood pressure (BP) and body weight were measured, and a blood sample was taken for determination of routine serum chemistries, plasma lipid and apolipoprotein concentrations, immunoreactive insulin (IRI), and plasma renin activity (PRA). Urinary 24 h excretion of sodium and potassium were measured. RESULTS: During the salt restriction period BP did not change, weight lowered, and PRA raised. There was a significant increase in serum level of creatinine, uric acid, IRI, total cholesterol and apo B, and a decrease in HDL cholesterol and apo A-I. CONCLUSION: As previously suggested, these observations seem to indicate that strict salt restriction may cause, at least in the short-term, adverse metabolic changes in hypertensive patients.