Elsevier

The Lancet

Volume 357, Issue 9259, 17 March 2001, Pages 848-851
The Lancet

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

https://doi.org/10.1016/S0140-6736(00)04199-4Get rights and content

Summary

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 allcause 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.

Introduction

The effect of high sodium intake on the risk of cardiovascular disease has long been debated. Much of this effect is thought to be mediated through raised blood pressure1, 2, 3, 4, 5 although experimental data indicate that other mechanisms might also be involved.6, 7 Even though there is substantial evidence that high salt intake can increase the risk of cardiovascular disease,8, 9, 10, 11, 12, 13 some investigators have argued that such an association may not exist and that low sodium intake might even be harmful.14, 15 A high salt intake has been suggested to be particularly harmful for obese people.16

Conflicting results from different studies might be due to various study designs and methods. 24 h urinary sodium excretion is regarded as the best way to measure sodium intake of an individual,17, 18 but collection of 24 h samples in large population studies is very difficult. Thus, alternative dietary methods have mostly been used in studies of the relation between sodium intake and cardiovascular disease. However, these methods are, subject to bias, and findings should be interpreted with caution.19, 20

We aimed to establish whether high sodium intake, measured by 24 h urinary sodium excretion, increases the risk of acute coronary heart disease and stroke events, and mortality from cardiovascular disease and all causes in the adult Finnish population.

Section snippets

Participants

We carried out baseline surveys in two eastern provinces, North Karelia and Kuopio, and in the Turku-Liomaa region in south-western Finland in 1982 and 1987.21, 22, 23 In both surveys, the sample included the age group 25–64 years. The 1982 and 1987 cohorts were combined in the analyses. The original random sample was stratified by four equally large 10-year age groups (25–34, 35–44, 45–54, and 55–64) and consisted of 3607 individuals, of whom 2834 (79%) provided 24 h urine samples. Another 233

Results

The median 24 h urinary sodium excretion was fairly high, 205 mmol in men (range 25–552) and 154 mmol in women (12–512). Mean values of 24 h sodium excretion were 216 mmol (SD 83) and 162 mmol (62) in men and women, respectively.

Mean age, concentration of serum cholesterol, and percentage of smokers did not differ across quartiles of 24 h sodium excretion in men and women (table 1). There was an increasing trend in the mean values of systolic and diastolic blood pressure and body mass index by

Discussion

We have shown that coronary heart disease, cardiovascular and all-cause mortality, and coronary heart disease frequency all rose significantly with increasing 24 h sodium excretion, independently of other cardiovascular risk factors, including blood pressure. Although the association between sodium excretion and morbidity and mortality was significant in men but not in women, the nonsignificant interaction between sex and sodium excretion for every outcome suggests that the effect of sodium on

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