Strengths and limitations of study
This was a large scale, community based salt reduction study targeting families in communities in eastern, central, and western regions of China. A stringent and standardised protocol was implemented at all study sites, with a high follow-up rate of 90%. An electronic data collection system was used to ensure high quality data collection. People who analysed the urine samples in the laboratory were blinded to whether the samples were from participants in the control or intervention group, which avoided potential bias in the sodium measurements.Our study also had some limitations. Firstly, we used 24 hour urine sodium excretion to evaluate the daily salt intake, which is acknowledged to be the most accurate method. However, single 24 hour urine collection provided limited information on dietary salt intake compared with multiple 24 hour urine collections. Secondly, the study outcomes (that is, 24 hour urinary sodium and blood pressure) were assessed at the start and at the end of the trial, so the change in the intervention effect over time could not be observed. Thirdly, the effect of the intervention measures was evaluated as a whole, which means that the independent effect of each measure could not be determined.