Ethnicity and the relationship of sodium intake to blood pressure.

Objective: To examine the impact of race on the relationship between sodium intake and blood pressure.

Methods: We examined the blood pressure levels and 24-h urinary sodium excretion of 808 (355 Black, 453 Caucasian) union members who participated in a workplace hypertension control program. The 808 study subjects, who met the criterion for accuracy of urine collection, included 627 untreated hypertensives (systolic blood pressure > or = 160 mmHg or diastolic blood pressure > or = 95 mmHg, or both) and 181 normotensives (blood pressure < 160/95 mmHg).

Results: In univariate analysis, the age-adjusted mean diastolic blood pressure levels of the Black subjects exceeded those of the Caucasian subjects at a significance level that was marginal for the male and very high for the female subjects. No differences were observed in mean systolic blood pressure between the Black and Caucasian subjects. Within each racial grouping, the subjects were grouped by sex-specific tertile of urinary sodium excretion in order to compare baseline characteristics and blood pressure levels. Small differences between the Black and Caucasian males in age-adjusted blood pressure within each urinary sodium excretion category were further diminished after adjusting for confounding factors. Significant differences between the Black and Caucasian females in age-adjusted diastolic blood pressure within each urinary sodium excretion group became non-significant when further adjusted for weight or body mass index, or both. These findings are in agreement with those observed in multiple linear regression models.

Conclusion: In this socio-economically homogeneous group, when confounding factors are considered, Black and Caucasian subjects have similar blood pressure levels at the same level of 24-h urinary sodium excretion. Ethnicity itself was not found to influence the relationship between sodium intake and blood pressure.