Table 1.

Description of Included Studies

Study (Country)	Study Design	Participants	Study Duration	Dietary Salt “Dose” (Actual Mean Intake per d)a	Method of Sodium Intake Measurement	Outcomes	Results
Cardiovascular major morbid events
Doukky et al. (US)12	Prospective cohort	N=833 HF patients overall, 42% male, mean age 63 y; N=260 in propensity‐matched analysis by sodium restriction; 45% male; mean age 64 y	36 mo	Overall: 8.3 g salt/d (range: 3.1–39.2 g salt/d). Mean salt intake for sodium‐restricted and sodium‐unrestricted groups not reported	57‐item FFQ	Primary outcome: composite of death and HF hospitalization; secondary outcomes: cardiac death and HF hospitalization	Sodium restriction was associated with an increased risk of death or HF hospitalization (HR 1.85; 95% CI 1.21–2.84) and HF hospitalization (HR, 1.82; 95% CI, 1.11–2.96).
Blood Pressure
Correia‐Costa et al. (Portugal)13	Cross‐sectional	N=298 children aged 8–9 y (sampled from “Generation XXI, Porto, Portugal” cohort); 53% male; mean age 8.8 y	Cross‐sectional	Total sample: 6.5 g salt/d Boys: 6.8 g salt/d Girls: 6.1 g salt/d	24‐h urine sodium excretion	24‐h ABPM	Every 1 g of salt intake was associated with an increase in daytime SBP by 0.56 mm Hg (95% CI, 0.11–1.01) in boys. No significant association in girls.
Ito et al. (Japan)14	Cross‐sectional	N=1501 adults (Shimane CoHRE study); 38% male; age 40–74 y. n=1005 without antihypertensive therapy; n=491 treated with antihypertensive therapy	Cross‐sectional	Taking diuretics: 10.5 g salt/d Without diuretics: 9.6 g salt/d	Spot urine sodium, estimated by Tanaka equation	SBP and DBP, using automatic sphygmomanometer	Sodium intake was positively associated with SBP in untreated (β=1.45, 95% CI, 0.93–1.96) and treated patients (β=0.75; 95% CI, 0.21–1.29). Sodium intake was positively associated with pulse pressure.
Iuchi et al. (Japan)15	Nonrandomized intervention study (pre‐/post‐study)	N=10 adults with type 2 diabetes and hypertension not treated with antihypertensive agents (7DACS); 70% male; mean age 60 y	7 d	Day 1: 9.8 g salt/d Day 7: 6.8 g salt/d	Urine sodium from casual urine samples, collected daily for 7 d, estimated using Tanaka equation	BP variability, using ABPM; body weight; plasma glucose and continuous glucose monitoring; ratio of low‐ to high‐frequency power; glycated hemoglobin, cholesterol, creatinine, plasma, and urinary C‐peptide	Short‐term salt restriction was not associated with significant change in SBP variability. There was a reduction in median SBP (–15 mm Hg, IQR −24 to −13 mm Hg).
Krupp et al. (Germany)16	Prospective cohort	N=206 young adults (DONALD study); 52% male; mean age 12 y during data collection at adolescence	Mean follow‐up not reported; study followed participants from infancy to young adulthood (age 18–25 y)	Boys: 6.7 g salt/d Girls: 6.1 g salt/d	Three 24‐h urine collections and three 3‐d food records (1 each per annum)	Office BP in young adulthood, using random‐zero or standard mercury sphygmomanometer	Sodium intake was associated with SBP in young adult men only (adjusted β coefficient 0.10 mm Hg per 1 mmol NaCl; 95% CI, 0.03–0.18), and was not associated with DBP.
Noh et al. (Korea)17	Cross‐sectional	N=24 096 adults (KNHANES 2007–2012); high BP group: 66.9% male, mean age 49.9 y; normal BP group: 48.1% male, mean age 40.8 y	Cross‐sectional	High BP group: 2585 mg sodium/1000 kcal Normal BP group: 2563 mg sodium/1000 kcal	24‐h dietary recall; high‐ and low‐sodium and potassium intake defined as above and below medians	Office BP, using a mercury sphygmomanometer; hypertension prevalence, defined as SBP ≥140 mm Hg or DBP ≥90 mm Hg	Low‐sodium:low‐potassium intake ratio and high‐sodium:low‐potassium intake ratio were associated with increased risk of high BP compared with low‐sodium:high‐potassium intake ratio (adjusted OR, 1.19; 95% CI, 1.01–1.40 and OR, 1.21; 95% CI, 1.02–1.44, respectively).
Thuesen et al. (Denmark)18	Cross‐sectional	N=3294 adults (Health 2006 study); 44.8% male; mean age 49.4 y	Cross‐sectional	Total sample: 8.99 g/d of salt	Random spot urine sodium, estimated using the Danish model formula	Office BP and fasting serum lipids	Estimated salt intake was positively associated with BP. Association was attenuated by adjustment for obesity (β 0.58 mm Hg/g salt; 95% CI, 0.20–0.97 for SBP, and 0.25 mm Hg/g salt 95% CI, 0.01–0.49 for DBP).
Umesawa et al. (Japan)19	Prospective cohort study	N=889 normotensive adults from Kyowa (CIRCS study); 33% male; mean age 75.3 y	Mean follow‐up: 5.8 y	Median urine sodium concentration: Quartile 1: 66 mmol/L Quartile 2: 107 mmol/L Quartile 3: 145 mmol/L Quartile 4: 193 mmol/L	Random spot urine sodium concentration at baseline	BP change from baseline, measured by sphygmomanometer	High urine sodium concentrations were associated with subsequent SBP increases (+7.0 mm Hg in highest quartile; +4.2 mm Hg in lowest quartile, P=.047) in patients with BMI <25, but not overweight patients.
Wang et al. (China)23	Meta‐analysis of quasi‐experimental studies and RCTs	N=3153 from 6 salt‐restriction studies N=3715 from 4 salt‐restriction spoon studies N=1730 from 4 salt‐substitute studies	Range: 1–8 wk for salt‐restriction studies Range: 3–12 mo for salt‐restriction spoon studies Range: 12–24 mo for salt‐substitute studies	For salt‐restriction studies: 1.8–7.7 g salt/d For salt‐restriction spoon studies: 5.3–11.2 g salt/d For salt‐substitute studies: 7.0–10.2 g salt/d	24‐h urine sodium excretion for salt‐restriction studies 24‐h urine sodium or salt weighing for salt‐restriction spoon studies First morning urine collection for salt‐substitute studies	BP; salt intake	Salt restriction was associated with 0.94 mm Hg/0.62 mm Hg reduction per 1 g of dietary salt restriction in hypertensive individuals. Use of salt‐restriction spoons with education was associated with a 1.46 g/d reduction in salt intake. Use of salt‐substitute reduced BP (–4.2/–0.6 mm Hg) in hypertensive individuals.
Yokokawa et al. (Thailand)20	Cross‐sectional	N=793 adults at high risk for cardiovascular disease (baseline data from RESIP‐CVD study); 51.8% male; mean age 66.5 y	Cross‐sectional	Total sample: 9.9 g salt/d Low salt intake (<10 g/d salt group): 8.3 g salt/d High salt intake (≥10.0 g/d salt group): 11.9 g salt/d	Overnight urine sodium (averaged over 3 consecutive d)	BP, measured with oscillometric device; presence of cardiovascular risk factors	Higher salt intake was associated with greater use of antihypertensive medications, family history of hypertension, and less awareness of high salt intake, compared with lower salt intake.
Kidney disease
Liu et al. (China)24	Meta‐analysis of observational studies	N=5638 from 9 studies (6 prospective, 3 cross‐sectional)	Range: 11 mo to 10 y for prospective studies; N/A for cross‐sectional studies	Only highest category of salt intake was extracted and this was variably reported	Various: food intake questionnaire, 24‐h recall, 24‐h urine sodium	CKD (defined as eGFR <60 mL/min/1.73 m2 or eGFR ≥60 mL/min/1.73 m2 with albuminuria)	Compared with the lowest sodium intake, highest sodium intake level was associated with an increased risk of CKD (pooled relative risk, 1.09; 95% CI, 1.01–1.19).
Other health outcomes
Huh et al. (Korea)21	Cross‐sectional	N=27 433 from South Korea (KNHANES 2008–2010); 42.9% male; mean age 51.5 y	Cross‐sectional	Lowest tertile: 6.1 g salt/d Middle tertile: 8.2 g salt/d Highest tertile: 10.8 g salt/d	Random spot urine sodium, estimated using Tanaka equation	NAFLD, assessed by HSI and FLI prediction scores; Hepatic fibrosis, assessed by BARD and FIB‐4 score in patients with FLI ≥60	High sodium intake was associated with an increased risk of NAFLD (adjusted OR, 1.39; 95% CI, 1.26–1.55 for HSI; OR, 1.75; 95% CI, 1.39–2.20 for FLI).
Lee et al. (Korea)22	Cross‐sectional	N=1467 children (KNHANES 2010–2011); 57.4% male; mean age 13.4 y	Cross‐sectional	Overall: 10.8 g salt/d Boys: 12.0 g salt/d Girls: 9.1 g salt/d	24‐h dietary recall; UNa/Cr measured by single spot urine	Overweight/obesity, by BMI; Central adiposity, by waist circumference; % body fat, by dual‐energy x‐ray absorptiometry	Sodium intake by recall was associated with BMI (OR for obesity 2.79; 95% CI, 1.66–4.68) and central adiposity (OR, 2.14; 95% CI, 1.25–3.67), but not % body fat. UNa/Cr was associated with obesity, central adiposity, and % body fat.

Abbreviations: ABPM, ambulatory blood pressure monitoring; BMI, body mass index; BP, blood pressure; CIRCS, Circulatory Risk in Communities Study; CKD, chronic kidney disease; CI, confidence interval; DBP, diastolic blood pressure; DONALD, Dortmund Nutritional and Anthropometric Longitudinally Designed Study; FFQ, food frequency questionnaire; FIB‐4, Fibrosis‐4 index; FLI, fatty liver index; eGFR, estimated glomerular filtration rate; HF, heart failure; HR, hazard ratio; HSI, hepatic steatosis index; IQR, interquartile range; KNHANES, Korea National Health and Nutrition Examination Survey; NaCl, sodium chloride; N/A, not applicable; NAFLD, nonalcoholic fatty liver disease; RCT, randomized controlled trial; RESIP‐CVD, Reducing Salt Intake for Prevention of Cardiovascular Diseases in High‐Risk Patients by Advanced Health Education Intervention study; SBP, systolic blood pressure; Shimane CoHRE, Center for the Community‐based Health Research and Education of Shimane University; UNa/Cr, urine sodium‐to‐creatinine ratio; US, United States; 7DACS, 7‐day Ambulatory Blood Pressure Monitoring and Continuous Glucose Monitoring Study.

^aUnless otherwise stated, units are in g per day of salt (sodium chloride) intake. To convert to mg per day of sodium, multiply by 400. To convert to mmol per day of sodium, multiply by 17.4.