Abstract 644: Salt Intake, Blood Pressure and Renal Function in a Black Population: A 5-Year Prospective Study

Abstract

Background: The salt debate continues, also regarding the WHO recommendation to restrict salt intake below 5 g/day. Black populations exhibit a high prevalence of salt-sensitivity, but no large-scale studies in these populations have been performed to show the cardiovascular consequences of dietary salt intake. Aim: To determine whether estimated daily salt intake is associated with BP and renal function cross-sectionally; and prospectively over 5-years. Methods: We included 1589 HIV-uninfected black participants aged > 30 yrs, and followed 1174 over 5 years (of which 151 died). We collected blood and fasting morning spot urine. The Kawasaki-formula was applied to estimate 24-h urinary sodium excretion. Using ANCOVAs we compared the following salt-intake groups: <3; 3-4; 5-6; 7-8; ≥9 g/day. Group sizes ranged from 84-499 participants. Results: Before and after adjustments baseline SBP tended to associate with estimated daily salt intake (adjusted p-trend=0.10). At baseline, there was no association of salt intake with estimated glomerular filtration rate (eGFR; p=0.65), but a strong positive association with albumin-to-creatinine ratio (p<0.001). Baseline daily salt intake of 5-6 g/day resulted in the smallest increase in SBP/DBP of 1.49/1.25 mmHg. Low daily salt intake of <3 and 3-4 g/day resulted in greater increases in BP than intakes of 5-6 g/day, namely SBP/DBP of 5.02/5.12 mmHg for < 3 mg/day (p for trend=0.034). The highest salt intake group (≥ 9 g/day) showed increases of 4.49/3.15 mmHg, albeit not significantly different from the 5-6 g/day group (p for trend=0.24). Regarding renal function, serum creatinine decreased from 101 to 65 μmol/L over 5 years, with an increase in eGFR from 114 to 129 ml/min/1.73 m 2 (both p<0.001). %eGFR increased according to salt intake (p-trend=0.038). Conclusion: Estimated daily salt intake relates weakly to BP cross-sectionally, but strongly with albuminuria. Prospectively, low salt intake of less than 5 g/day predicts a significant elevation in SBP compared to 5-6 g/day. In contrast to healthy white populations indicating a decrease in GFR with age, we found an increase over 5 years, which is related to salt intake, suggesting a high prevalence of salt-sensitivity in this black population.