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.