High salt intake promotes a decline in renal function in hypertensive patients: a 10-year observational study

We investigated the influence of long-term salt load on renal function in hypertensive patients. The subjects were 133 hypertensive patients (80 women and 53 men, mean age 60 +/- 9 years) who underwent at least five successful 24 h home urine collections during the 10-year observation period. Blood pressure (BP) and 24-h urinary salt and creatinine excretion levels were measured. BP decreased from 143 +/- 12/85 +/- 8 to 129 +/- 14/68 +/- 11 mmHg during the 10.5-year observation period, and this decrease was associated with patients taking an increased number of antihypertensive drugs (1.3 +/- 1.0 to 2.2 +/- 1.1). The estimated glomerular filtration rate (eGFR) also significantly decreased from 71.7 +/- 14.6 to 64.7 +/- 16.5 ml min(-1) (P<0.01), and the change in eGFR was -0.68 ml min(-1) per year on average. The average salt excretion was 8.6 +/- 2.2 g per day and showed a significant negative correlation with the change in eGFR (r = -0.21, P = 0.02). Subjects with an average salt excretion <8 g per day showed a significantly slower decline in renal function than those with an average salt excretion >= 8g per day (the change in eGFR: -0.41 +/- 1.10 vs. -0.83 +/- 1.19 ml min(-1) per year, P<0.05). In the multivariate analysis, the average salt excretion (partial r=-0.19, P=0.03) and baseline eGFR (partial r=-0.23, P=0.01) were significantly associated with the change in eGFR. This association was independent of BP change or an increased number of antihypertensive drugs. The results suggest that long-term salt load promotes a decline in renal function in hypertensive patients; thus, salt restriction is encouraged, to prevent renal damage. Hypertension Research (2013) 36, 172-176; doi: 10.1038/hr.2012.155;published online 11 October 2012