Effect of salt intake on blood pressure in patients receiving antihypertensive therapy: Shimane CoHRE Study

Background: Salt intake is recognized as an important risk factor for hypertension in the general population. On the other hand, the availability of various classes of antihypertensive drugs means that it is generally not considered crucial to control the salt intake of hypertensive patients. In this study, we evaluated whether blood pressure (BP) was correlated with 24-hour salt intake in patients receiving antihypertensive therapy.

Methods: A total of 1496 consecutive participants undergoing health screening examinations were recruited. Subjects were divided into two groups according to their antihypertensive medications checked on prescriptions: 1005 subjects without antihypertensive therapy (untreated subjects) and 491 subjects with antihypertensive therapy (treated subjects). The 24-hour urinary sodium excretion (24h-uNa), a surrogate marker for daily salt intake, was estimated with the formula proposed by Tanaka et al. in 2002.

Results: Univariate analysis indicated that 24h-uNa was positively correlated with the systolic BP of both untreated and treated subjects. This was confirmed by multiple linear regression analysis after adjustment for confounding factors (untreated subjects: partial regression coefficient β=1.45 ± 0.26, p<0.001; treated subjects: β=0.75 ± 0.27, p=0.01). Salt intake was also correlated with the pulse pressure in both treated subjects (β=0.55 ± 0.24, p=0.02) and untreated subjects (β=0.93 ± 0.19, p<0.001).

Conclusion: These results suggest the importance of reducing salt intake in hypertensive patients on pharmacotherapy, as well as in the general population. Further studies of hypertensive patients employing 24-h urine collection are warranted to confirm the present findings.