[Comparison of estimated salt and potassium intake and urinary sodium-to-potassium ratio based on casual urine: A 10-year follow-up of NIPPON DATA2010].

Abstract

Objectives　This study compared the estimated 24-hour salt intake, estimated 24-hour potassium intake, and sodium-to-potassium (Na/K) ratio based on casual urine samples from the general Japanese population at baseline and 10 years later.Methods　NIPPON DATA2010 is a cohort study of participants in the 2010 National Health and Nutrition Survey of Japan; 2,244 individuals were included in the 2020 follow-up survey of NIPPON DATA2010. Among them, 798 individuals consented to participate in urine testing and were sent a self-collection kit. The estimated 24-hour salt intake (g/day) and estimated 24-hour potassium intake (mg/day) were calculated using Tanaka's formula, and the urinary Na/K ratio (mmol/mmol) was also determined. A total of 667 participants provided valid urine data at both baseline and 10 years later (mean age at baseline: 54.8±13.4 years; women: 59.1%). Participants were classified into four groups according to sex and age at baseline: men aged ＜60 years, men aged ≥60 years, women aged ＜60 years, and women aged ≥60 years. Regions were categorized into seven areas in Japan. Comparisons between baseline and 10 years later were performed using paired t-tests.Results　Differences in the estimated 24-hour salt intake were not statistically significant for all groups. The estimated 24-hour potassium intake was higher 10 years later in men aged ≥60 years and in women; men aged ＜60 years showed a trend toward higher values. The urinary Na/K ratio was significantly lower 10 years later in men aged ≥60 years (baseline: 4.14±2.57, 10 years later: 3.38±2.10, P = 0.002), women aged ＜60 years (baseline: 4.05±2.23, 10 years later: 3.44±1.91, P＜0.001), and women aged ≥60 years (baseline: 3.76±1.79, 10 years later: 3.03±1.78, P＜0.001). Further, the urinary Na/K ratio was significantly lower in the Tohoku, Kanto, and Kinki regions.Conclusion　Findings of the current study revealed that the estimated 24-hour potassium intake was significantly higher and urinary Na/K ratios were significantly lower 10 years after initial samples were taken at baseline, particularly in women and men aged ≥60 years, as well as in specific regions. These findings suggest the need to strengthen the measures for specific target groups and regions.