Hyperosmolarity and Increased Serum Sodium Concentration Are Risks for Developing Hypertension Regardless of Salt Intake: A Five-Year Cohort Study in Japan.

Masanari Kuwabara,Bernardo Rodriguez-Iturbe,Ichiro Hisatome,Mehmet Kanbay,Koichiro Niwa,Ryusuke Ae,Gabriela Garcia,Ana Andres-Hernando,Carlos Roncal-Jimenez,Laura Sánchez-Lozada,Miguel Lanaspa,Richard Johnson

doi:10.3390/nu12051422

Abstract

The potential contribution of serum osmolarity in the modulation of blood pressure has not been evaluated. This study was done to examine the relationship between hyperosmolarity and hypertension in a five-year longitudinal design. We enrolled 10,157 normotensive subjects without diabetes who developed hypertension subsequently as determined by annual medical examination in St. Luke’s International Hospital, Tokyo, between 2004 and 2009. High salt intake was defined as >12 g/day by a self-answered questionnaire and hyperosmolarity was defined as >293 mOsm/L serum osmolarity, calculated using serum sodium, fasting blood glucose, and blood urea nitrogen. Statistical analyses included adjustments for age, gender, body mass index, smoking, drinking alcohol, dyslipidemia, hyperuricemia, and chronic kidney disease. In the patients with normal osmolarity, the group with high salt intake had a higher cumulative incidence of hypertension than the group with normal salt intake (8.4% versus 6.7%, p = 0.023). In contrast, in the patients with high osmolarity, the cumulative incidence of hypertension was similar in the group with high salt intake and in the group with normal salt intake (13.1% versus 12.9%, p = 0.84). The patients with hyperosmolarity had a higher incidence of hypertension over five years compared to that of the normal osmolarity group (p < 0.001). After multiple adjustments, elevated osmolarity was an independent risk for developing hypertension (OR (odds ratio), 1.025; 95% CI (confidence interval), 1.006–1.044), regardless of the amount of salt intake. When analyzed in relation to each element of calculated osmolarity, serum sodium and fasting blood glucose were independent risks for developing hypertension. Our results suggest that hyperosmolarity is a risk for developing hypertension regardless of salt intake.

Highlights

Salt intake is higher in Japan than in western societies, and averages more than 11 g per day inJapan and approximately 10 g per day in western countries [1,2]
We evaluated the risk for hypertension in those with baseline hyperosmolarity compared with the normal osmolarity group, and the risk was significantly greater in the hyperosmolar group
For every 1 mmol/L rise in serum sodium the risk for hypertension was increased by 4.5%, and for those with serum sodium >144 mmol/L, the cumulative incidence of hypertension over five years was 14.8% compared to 7.5% in those with a serum sodium of

Summary

Introduction

Salt intake is higher in Japan than in western societies, and averages more than 11 g per day in. Japan and approximately 10 g per day in western countries [1,2]. There is extensive evidence that high salt intake is associated with hypertension, obesity, diabetes, and cardiovascular disease [2,3]. Salt intake is associated with calorie intake, and calorie intake is directly associated with obesity, diabetes, and hypertension. It is difficult to assess the direct association between salt intake and blood pressure. Some studies showed that salt intake below 6 g is associated with increased cardiovascular disease and increased all-cause mortality [4,5]. Wald, et al reported that a low serum sodium is associated with increased mortality risk [6]

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Conclusion