ArticlesUrinary sodium excretion and cardiovascular mortality in Finland: a prospective study
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.
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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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