Sodium excretion and blood pressure.

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Abstract
The urinary excretion of Na, K and water during three 24 h periods were related to blood pressure in a sample of 49 yr old men. Of 3205 men aged 45 yr living in Goteborg, Sweden, 2376 (74%) took part in the blood pressure screening; of these 120 subjects having blood pressures from the lowest to the highest were selected by systematic sampling based on diastolic blood pressure. Only subjects who were not on antihypertensive treatment were included. A marked day-to-day variation was shown in Na excretion, with between-days r values of 0.23-0.64. The variation was less for 2 consecutive days than for 2 nonconsecutive days. The mean urinary excretion and the diurnal rhythm of Na, K and water did not differ significantly among normotensive, borderline and hypertensive subjects. Over a wide range of blood pressures, no correlation was found between blood pressure and the urinary excretion of Na, K or water. In the low blood pressure range, there was a significant positive correlation between blood pressure and urinary Na excretion (R = 0.46, P < 0.01; R = Spearman''s coefficient of rank correlation). The large intraindividual variation in Na excretion and blood pressure makes it difficult to estimate an individual''s mean values. There are limitations in drawing longitudinal conclusions from cross-sectional data. With these methodological problems in mind, the findings indicate that salt intake influences blood pressure in a part of the normotensive population, but do not lend support to the hypothesis that habitual salt intake might be of major importance for the blood pressure level in mild to moderate essential hypertension.