Altitudes of residential areas affect salt intake in a rural area in Japan: a Shimane CoHRE Study

There is increasing evidence of an association between residential environments and hypertension. As shown in our previous study, the inconvenience of the locations of residential areas may be one of the factors influencing the blood pressures of inhabitants. Salt intake is one of the likely mediators between inconvenience and hypertension. Therefore, in this study, we evaluated the association between the altitudes of residential areas and salt intake in a rural Japanese region because altitude may be one of the proxies for inconvenience. In this cross-sectional study, 1016 participants living in a mountainous region in Japan were recruited during health examinations. The altitude of each participant's residence was estimated using a geographic information system. Subjects were divided into quartile groups according to the altitudes of their residences. To evaluate salt intake, we employed the 24-h salt intake estimation of Kawano et al. (e24-h salt intake) and the urinary sodium-to-potassium ratio (uNa/K). Linear regression analyses indicated that altitude was an independent factor influencing both e24-h salt intake and uNa/K after adjustments for age, sex, body mass index, physical activity, alcohol consumption, triglycerides and county of residence. The same result was observed when the subjects who did not take antihypertensive medications were analyzed (N=633). The present study indicated that altitude of residence had a significant positive influence on salt intake in a rural area of Japan.