Body mass index and associations of sodium and potassium with blood pressure in INTERSALT.

Abstract

This report further examines the relation of body mass index (BMI) to associations of 24-hour urinary sodium, potassium, and sodium-potassium ratio with blood pressure in INTERSALT, a 52-center international study of electrolytes and blood pressure. Analyses without adjustment for BMI indicated average systolic pressure greater by 6.00 mm Hg per 100 mmol higher sodium and diastolic by 2.52 mm Hg. With adjustment for BMI, these values were reduced to 3.14 and 0.14 mm Hg, respectively. For the sodium-potassium ratio, blood pressure associations were stronger when not adjusted for BMI, and for potassium, adjustment generally had little effect. To explore possible interactions of these variables with BMI in relation to blood pressure, the 52 centers were divided into two groups of 26 based on whether the center median for BMI was less than or greater than or equal to 24.5 kg/m 2 , and individuals within each of the 52 centers were classified into lower-or higher-BMI groups based on individual BMI less than or greater than or equal to 24.1 kg/m 2 . Sodium and the I NTERSALT is an international study of the relations of electrolyte excretion and other factors to blood pressure carried out in 52 centers from 32 countries. Previous reports from INTERSALT indicated that body mass index (BMI), 24-hour urinary sodium and potassium excretions, and the sodiumpotassium ratio were all independently related to blood pressure of individuals 13 and that sodium and potassium excretions of individuals were both positively correlated with BMI.2 In addition, pooled regression coefficients for sodium, potassium, and sodium-potassium ratio with blood pressure that were adjusted only for age and sex when compared with the coefficients also adjusted for alcohol intake and BMI (as well as potassium for sodium, and sodium for potassium) suggested that adjustment for BMI had a substantial effect on observed electrolyte-blood pressure associations in INTERSALT. Correspondence to Dr Alan R. Dyer, Department of Preventive Medicine, Northwestern University Medical School, 680 N Lake Shore Dr, Suite 1102, Chicago, IL 60611. sodium-potassium ratio were positively and significantly and potassium inversely and significantly related to systolic pressure in all four of these subgroups, and the sodium-potassium ratio and potassium were related to diastolic pressure in two and three subgroups, respectively. Electrolyte-blood pressure associations did not differ significantly between the two subgroups of centers or between the two subgroups based on individuals. Although these results indicate that adjustment for BMI has an important effect on INTERSALT associations of sodium and the sodium-potassium ratio with blood pressure and may represent an overadjustment, they also indicate that each of the three variables is related to blood pressure throughout the BMI range. Thus, they do not support the concept of important interactions of sodium and potassium with BMI in relation to blood pressure. Intervention studies of the effects of weight loss, ...

Dietary magnesium intake and blood pressure: a qualitative overview of the observational studies

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Salt intake of the Slovene population assessed by 24 h urinary sodium excretion

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INTERMAP: background, aims, design, methods, and descriptive statistics (nondietary)

“…21 Results on sodium and blood pressure in INTER-SALT prevailed for younger (ages 20-39 years) and older (ages 40-49 years) participants, with coefficients about two to three times larger for older than younger; results also prevailed for men and women, and for nonoverweight and overweight persons. 32,33 Analyses were also performed on best fit for the sodium-SBP relation. Linear and exponential fits were virtually identical in their multivariate adjusted Z score, measuring goodness of fit.…”