Findings from recent large population studies have provided conflicting information about the advantages of lowering sodium in the treatment of patients with hypertension. Graudal and colleagues reviewed the literature to determine the effects of dietary sodium restriction on systolic and diastolic blood pressures, and renin, aldosterone and lipid levels.

The authors conducted a Medline search for randomized studies of sodium intake and hypertension. Studies were included if they evaluated at least one of the following effect parameters: body weight, amount of sodium reduction, systolic and diastolic blood pressure before and after the intervention, and renin, aldosterone and lipid levels before and after the intervention.

The search yielded 58 studies including hypertensive patients and 56 studies including normotensive patients. These studies were integrated into two separate meta-analyses. In the hypertensive patients, a mean reduction in sodium intake of 118 mEq per L (118 mmol per L) per day led to decreases of 3.9 mm Hg and 1.9 mm Hg in systolic and diastolic blood pressures, respectively. In the normotensive patients, a mean reduction in sodium intake of 160 mEq per L (160 mmol per L) per day led to decreases of 1.2 mm Hg and 0.26 mm Hg in systolic and diastolic blood pressures, respectively. Renin and aldosterone levels increased significantly in patients with reduced sodium intake. Lipid levels were adversely affected in patients who undertook short-term high reductions in sodium intake. It is not known if these effects are clinically significant.

The authors conclude that the effects of sodium reduction on blood pressure in normotensive patients do not support a general recommendation for a sodium-restricted diet in this population. Sodium reduction may be recommended as an adjunctive treatment in patients with hypertension. However, studies evaluating hard end points (i.e., myocardial infarction, stroke and death) instead of those assessing substitute end points, such as blood pressure, are necessary before the usefulness of sodium-restricted diets can be truly judged.