Relationship of urinary sodium and sodium-to-potassium ratio to blood pressure in older adults in Australia

Objective: To assess the relationship between dietary sodium intake, as measured by urinary electrolyte excretion, and blood pressure within a population of older Australian adults. Design, setting and participants: A cross-sectional study of adults enrolled in the Melbourne Collaborative Cohort Study, stratified by sex, country of birth (Italy, Greece, Australia/New Zealand) and age (50-59 and 60-75 years). Blood pressure measurements were taken in 2003-2007 and 24-hour urine collections in 2007-2008. Main outcome measures: 24-hour urinary excretion of sodium and potassium, urinary sodium-to-potassium ratio, and clinic blood pressure measurement. Results: The mean +/- SD age of 783 participants was 64.0 +/- 6.3 years. Mean SD urinary sodium was 155.1 +/- 63.1 mmol/day (8.9 +/- 3.6 g salt/day), urinary potassium was 82.3 +/- 27.9 mmol/day, and urinary sodium-to-potassium ratio was 1.99 +/- 0.83. In the 587 participants with blood pressure measurements, urinary sodium and the sodium-to-potassium ratio were both associated with systolic blood pressure in all adjusted and unadjusted models (mmHg change per 100 mmol/day increase in sodium: regression coefficient, 2.3, 95% CI, 0.1-4.6; P = 0.049, adjusted for age, sex, body mass index, country of birth and antihypertensive medication use). Conclusion: This study has demonstrated, for the first time within an Australian population sample of older adults, that sodium intake is positively associated with blood pressure. These results suggest that a population-wide reduction in sodium intake could be effective in reducing blood pressure in adults in Australia. MJA 2011; 195:128-132