SODIUM AND BLOOD-PRESSURE - A REVIEW OF THE EVIDENCE FROM CONTROLLED TRIALS OF SODIUM REDUCTION AND EPIDEMIOLOGIC STUDIES

Evidence from controlled trials of sodium reduction and epidemiological studies are consistent in showing that lower urinary sodium excretion is associated with lower blood pressures (BPs) and quantitatively they give similar estimates of effect. An overview of randomised controlled trials gave the estimate that a reduction in sodium excretion averaging 70 to 75 mmol per day lowered BP in hypertensives by 4.9 mm Hg systolic and 2.6 mm Hg diastolic (p < .001), and by 1.7 mm Hg (p < .001) and 1.0 mm Hg (p < .01) respectively in normotensives. An overview of within-population epidemiological studies, after correction for intra-individual variability in sodium excretion, gave a pooled (simple) regression estimate that 100 mmol lower sodium was associated with BP lower by 3.7 mm Hg systolic and 2.0 mm Hg diastolic (p < .001); and the corrected pooled within-centre regression estimate from INTERSALT, with adjustment for age and sex, was that 100 mmol lower sodium was associated with BP lower by 3.5 mm Hg systolic and 1.5 mm Hg diastolic (p < .001), reducing to 2.2 mm Hg (p < .001) and 0.1 mm Hg respectively after adjustment for other confounders. Across the centres in INTERSALT, average sodium excretion was positively and significantly related to slope of BP with age, such that 100 mmol lower sodium was associated with a 9 mm Hg lower rise in systolic BP from age 25 to age 55 (p < .001). Results of long-term epidemiological studies indicate that average BPs lower by 2-3 mm Hg are associated with differences in coronary heart disease (CHD) mortality rates of 4-5 per cent and stroke mortality rates of 6-8 per cent. Strategies to lower sodium intake in the community so as to reduce the population burden of CHD and stroke, need to address the issue of the large amounts of sodium which are added in food manufacture.