Salt restriction induced hyponatremia in hypertensive patients: case control study

Abstract

BACKGROUND: Salt intake is essential to life. Despite the physiological need of salt, when taken in excess, it is linked to raised blood pressure; hence many guidelines for treatment of hypertension recommend salt restriction to control blood pressure. WHO recommends a sodium intake of 2 g per day. Rwanda, as any other east Africa country, has a low sodium diet intake with an average of 1.6 g per day per person. Despite this low salt intake, national protocol for treatment of hypertension still recommends a salt restriction. As any other developing country, Rwanda population protein intake is low too. When combined, low salt intake and low protein intake, they lead to low solute intake, a condition known to cause hyponatremia by decreasing free water excretion capacity. Hyponatremia, especially in elderly has many adverse outcomes including poor cognitive function, and some studies suggested that low salt intake might be linked with increased mortality as do high salt intake. METHODOLOGY: Main objective of the study was to determine association between salt restriction and hyponatremia in hypertensive patients. Secondary objectives were to determine prevalence of salt restriction and to determine other possible risk factors of hyponatremia in hypertensive patients on treatments. A case control study was conducted on adult hypertensive patients in two main tertiary hospitals in Kigali. Cases were defined as hypertensive patients with hyponatremia and Controls were defined as hypertensive patients without hyponatremia. Outcome was hyponatremia. Exposure was salt restriction. Cases and Controls were matched on age, gender, use of diuretics and duration of hypertension treatment. vi | P a g e

Results: 245 participants were selected; out of them, 110 (44.9%) were cases and controls were 135 (55.1%). 159 (64.8%) participants were salt restricted and out of them, 74 (46.5%) were taking salt free diet. Among cases 98 (89.1%) were exposed and in controls 61 (45.1%) were exposed. Odd ratio of having hyponatremia if exposed was 9.90 (95%CI, P-value<0.001). Evaluation of other risk factors of hyponatremia in hypertensive patients revealed an odd ratio of 3.00 and 2.33 with p-value: 0.060 and 0.090 of getting hyponatremia for heart disease and renal disease patients respectively. Odds of having hyponatremia when using diuretics were 1.652 with a p-value: 0.208 in thiazide diuretics and 1.66 with a p-value: 0.197 in loop diuretics. Odd ratio of getting hyponatremia for patients aged above 35 years was 1.930 with a p-value: 0.925 compared to patients aged of 25-35 years. Odds of hyponatremia in patients who have been hypertensive for more than 5 years is 1.510 with a p-value: 0.110 compared to odds of 0.287 with a p-value of 0.063 observed in first year of hypertension. Conclusion: Our study revealed a strong association between salt restriction and hyponatremia in hypertensive patients on treatment. Heart disease, renal disease, use of diuretics, advanced age and long duration on treatment of hypertension showed an association with hyponatremia in hypertensive patients but this association is not significant.