Urinary sodium excretion and cardiovascular mortality in Finland: a prospective study

Abstract

Background: The evidence that high salt intake increases the risk of cardiovascular disease has been challenged. We aimed to find out whether salt intake, measured by 24 h urinary sodium excretion, is an independent risk factor for cardiovascular disease frequency and mortality, and all-cause mortality.

Methods: We prospectively followed 1173 Finnish men and 1263 women aged 25-64 years with complete data on 24 h urinary sodium excretion and cardiovascular risk factors. The endpoints were an incident coronary and stroke event, and death from coronary heart disease, cardiovascular disease, and any cause. Each endpoint was analysed separately with the Cox proportional hazards model.

Findings: The hazards ratios for coronary heart disease, cardiovascular disease, and all-cause mortality, associated with a 100 mmol increase in 24 h urinary sodium excretion, were 1.51 (95% CI 1.14-2.00), 1.45 (1.14-1.84), and 1.26 (1.06-1.50), respectively, in both men and women. The frequency of acute coronary events, but not acute stroke events, rose significantly with increasing sodium excretion. When analyses were done separately for each sex, the risk ratios were significant in men only. There was a significant interaction between sodium excretion and body mass index for cardiovascular and total mortality; sodium predicted mortality in men who were overweight. Correction for the regression dilution bias increased the hazards ratios markedly.

Interpretation: High sodium intake predicted mortality and risk of coronary heart disease, independent of other cardiovascular risk factors, including blood pressure. These results provide direct evidence of the harmful effects of high salt intake in the adult population.