Urine 24-Hour Sodium Excretion Decreased between 1953 and 2014 in Japan, but Estimated Intake Still Exceeds the WHO Recommendation.

Background: Accurate monitoring of sodium intake is necessary for evaluating strategies used to reduce sodium intake. However, no repeat survey has been conducted in representative populations in Japan to examine trends in sodium intake with the use of 24-h urinary sodium excretion, a standard evaluation method for sodium intake monitoring. Objective: The objective of this study was to examine potential trends in sodium intake by examining previous reports of 24-h urinary sodium excretion in healthy Japanese adult populations. Methods: We systematically searched for reports of 24-h urinary sodium excretion in healthy Japanese adult populations (mean age range: 18-69 y). We searched PubMed and Web of Science for English-language articles and hand-searched 7 Japanese scientific journals for Japanese-language articles. Trends in urinary sodium excretion were examined with the use of weighted linear regression and random-effects meta-regression analyses, with adjustment or stratification to address study characteristics (population mean age, percentage of men, and sample size) and study assessment for completeness of urine collection. Results: We identified 68 reports of urinary sodium excretion from 53 articles published from 1953 through 2014 that showed high rates of urinary sodium excretion in healthy Japanese adult populations (weighted mean: 4900 mg/d). The rate of urinary sodium excretion significantly decreased between 1953 and 2014, by 4350 mg/d ( P < 0.001); however, the rate of reduction in urinary sodium excretion was variable and decreased with time ( P -linear trend <0.001 and P -quadratic trend <0.001). In the random-effects meta-regression analysis of studies that assessed completeness of urine collection with creatinine excretion, no significant relation between urinary sodium excretion and year was observed from 1978 to 2014 (β = -16, P = 0.40). Conclusion: Despite a decrease in urinary sodium excretion in healthy Japanese adult populations between 1953 and 2014, sodium intake still exceeds the WHO recommendation for adults. This review was registered at PROSPERO as CRD42016035452.