China.

Methods	Open‐cohort study (in addition to ongoing participants, replenishment samples are recruited at each wave)
Participants	1991, 1993, 1997, 2000, 2004, 2006 and 2009: multi‐stage, random‐cluster process used to recruit adults 20 to 60 years of age from Heilongjiang, Liaoning, Jiangsu, Shandong, Henan, Hubei, Hunan, Guizhou and Guangxi
Interventions	Salt reduction initiative began in 2006. Efforts included: public information/education campaign.
Outcomes	1991, 1993, 1997, 2000, 2004, 2006 and 2009: mean sodium intake (grams/d) estimated from dietary data obtained from 3 consecutive 24‐hour dietary recalls and condiment and food weights
Axes of inequality	1991, 1993, 1997, 2000, 2004, 2006 and 2009: gender, place of residence, education and income
Sample size and response rate	1991, 1993, 1997, 2000, 2004, 2006 and 2009: n = 16,869, ˜ 88% at inception at the individual level and 90% at the household level
Funding source / Conflict of Interest (COI)	1991, 1993, 1997, 2000, 2004, 2006 and 2009: funding source not provided/no COI declared by study authors
Notes	Sources of data points and references: see China 1991, 1993, 1997, 2000, 2004, 2006 and 2009: *Du S, Neiman A, Batis C, Wang H, Zhang B, Zhang J, Popkin BM. Understanding the patterns and trends of sodium intake, potassium intake, and sodium to potassium ratio and their effect on hypertension in China. American Journal of Clinical Nutrition 2014;99:334‐343 2011 data point from Shandong province only: Bi Z, Liang X, Xu A, Wang L, Shi X, Zhao W et al. Hypertension prevalence, awareness, treatment, and control and sodium intake in Shadong province, China: baseline results from Shadong‐Ministry of Health Action on Salt Reduction and Hypertension (SMASH). Preventing Chronic Disease 2011;11(E88) *Indicates main publication used for in‐text citation purposes
Risk of bias
Bias	Authors' judgement	Support for judgement
Sampling	Low risk	Sample was selected from 9 Chinese provinces through a multi‐stage random‐cluster process
Confounding	High risk	Uncontrolled study designs always score 'high'
Reliability/validity of outcome measure	Low risk	3 consecutive 24‐hour dietary recalls were used to measure sodium levels, both at household and individual levels. Validation of the dietary survey method was described
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Pre‐existing data were used to evaluate the initiative
Representativeness of sample	Unclear risk	Representativeness of the sample of the Chinese population was not discussed
Selective reporting (reporting bias)	Low risk	Means and standard deviations were reported for all years
Other bias	Low risk	Changes to the Chinese food environment may contribute to decreased sodium levels, including “marked advancements in the transportation of food”, and “added salt intake has decreased faster in the North than in the South” (Du 2014, pg. 339). Refrigerator ownership, among other changes, has increased as the result of “rapid modernization and urbanization” (Du 2014, pg. 340), thus salt is no longer needed as a major food preservative. Study authors discuss these potential reasons for salt reduction but do not account for them in their analysis. However, these issues are captured under the "confounding" domain