Association of dietary salt intake with diabetes mellitus in the Japanese general population
Authors: Nakano S , Takase H , Hayashi K , Kin F , Isogaki T , Takayama S , Dohi Y 
Published: November 2023

Abstract

Background/Introduction
Excess salt intake, one of the most important modifiable factors in our lifestyle, has been reported to be a risk of cardiovascular morbidity and mortality. Several mechanisms underlying the development of cardiovascular disease after excess salt intake are proposed, among which hypertension has been established. Diabetes mellitus (DM) is also a risk factor of cardiovascular disease and, thus, there may be some association between excess salt intake and DM.

Purpose
The present study was designed to investigate possible relationship between dietary salt intake and DM in the general population.

Methods
Dietary salt intake was estimated using a spot urine sample in 16018 subjects (male=9642, 52.0±12.3 year-old) who visited our hospital for a yearly physical checkup from July 2008 to March 2019 (baseline). A cross-sectional analysis for the relationship between salt intake and DM was performed at baseline. Then, subjects without DM (n=14715, male=8651, 51.3±12.3 year-old) were followed up until March 2020 (median 2107 days) with the endpoint being the development of DM. DM was defined as fasting plasma glucose (FPG) ≥126mg/dL, HbA1c≥6.5% or the use of antidiabetic medications.

Results
A cross-sectional analysis revealed that salt intake in subjects was 8.67±1.98 g/day. Salt intake was significantly higher in subjects with (n=1280) than without DM (9.55±2.17 vs. 8.61±1.94 g/day). Multivariate regression analysis adjusted for age, gender, body weight, systolic blood pressure, pulse rate, serum creatinine, uric acid, FPG, LDL-cholesterol, triglyceride, current smoking and frequent alcohol drink showed that salt intake was associated with the presence of DM (r=0.027, p&lt;0.001). In the follow-up study, 861 subjects developed DM (10.1 per 1000 person-year), with the incidence being more frequent in males than in females (11.7 vs. 7.6 per 1,000 person-year). The incidence of DM was increased across the quartiles of salt intake at baseline (7.5, 7.6, 10.5 and 14.8 per 1000 person-year). In analysis where salt intake at baseline was taken as continuous variables, non-adjusted hazard ratio (HR) (95% confidence interval [CI]) of salt intake for the new onset of DM was 1.146 (1.109-1.184). Multivariate Cox-hazard analysis adjusted for possible risk factors showed that salt intake was a significant predictor for the future development of DM (HR: 1.037, 95%CI: 1.001-1.073), while additional adjustment for baseline body weight disappeared the statistical significance (HR: 0.994, 95%CI: 0.958-1.031).

Conclusions
Salt intake is associated with the development of DM and excess salt intake may predict future development of DM in the general population. Excess food intake which is usually accompanied by excess salt intake in individuals with increased body weight may be responsible for the development of DM. Maintenance of appropriate body weight as well as restriction of dietary salt may lead to the prevention from developing DM.