Sodium excretion and blood pressure in middle-aged men in the Sogn County: an intra- and interpopulation study.

Blood pressure (BP) and daily sodium excretion were measured in 262 males aged 35-54 years from three separate districts of the Sogn county in Norway. Averages for mean arterial pressure and sodium excretion were 103.4 mmHg and 192.4 mmol/24 h respectively, which is similar to the excretion rates in most other Western societies. Interpopulation (between groups) analysis revealed statistically significant differences in sodium excretion and BP between the three districts, but no significant correlation was found between individual sodium excretion rates and the respective BPs (within group analysis). The mean urinary sodium/potassium ratio (Na/K) was significantly lower in the district with the lower BP level, but there was no statistically significant correlation between individual Na/K ratios and BP. The lack of significant correlation between sodium excretion and BP in the within group analysis as opposed to the between groups comparison could be due to large intra-individual variation of sodium excretion.