1. Research background

   - High blood pressure is one of the most important risk factors to cardiovascular diseases (CVDs). Reducing population blood pressure can control CVD incidence and lower mortality effectively. Much research has proven that adjusting for Na and K intake level can reduce blood pressure. According to the China Salt Substitute Study, the systolic blood pressure of intervention group which used salt substitute is 5.4 mmHg lower than that of control group. Life expectancy in Tibet is 67 years old. It is estimated that the use of salt substitute among population in Tibet can reduce total mortality in Tibet by 20%. China Salt Substitute Study in Tibet (CSSS-Tibet), found that salt substitute is effective in lowering both systolic and diastolic blood pressure and offers a simple, low-cost approach for hypertension control among Tibetans in China (unpublished results). However, the study focused on hypertensive patients, the effectiveness of hypertension control by providing free salt substitute to the entire population remains unknown, and a large-scale trial is needed.

2. Objectives

   - Primary objective is to observe the effect of providing salt substitute on population blood pressure in Tibet. Secondary objective is to observe the effect of such intervention on population mortality, cardiovascular mortality and life expectancy. In addition, the data collected from high-risk population (sub-group) in the study will be used in China Salt Substitute and Stroke Study (SSaSS). Also, serum cholesterol and random blood glucose of people over 60 in Tibet will be collected.

3. Method

   • The study is a open, cluster-randomized, controlled trial.
   • 30 villages with 15 to 35 households each and a distance of at least five kilometers in between will be selected from Damxung county and Maizhokunggar county. The two counties have an average altitude of over 4000 meters in Tibet Autonomous Region.
   • All selected villages will be randomly assigned to intervention group or control group on a 1:1 ratio.
   • All household in the selected villages will be recruited if they meet the eligibility criteria. Approximately 4,500 participants will be enrolled
   • Intervention group receives free salt substitute. Control group will continue to buy their own normal salt. Both group will receive the same health education on salt reduction.

4. Outcome - Primary outcome is blood pressure. Secondary outcomes include total mortality, cardiovascular disease mortality, life expectancy, serum cholesterol level of people over 60, and random blood glucose level of people over 60.

Inclusion Criteria:

• All family households in the selected satellite village will be invited to participate in the study

Family households will be excluded from participating if they meet one or more of the following exclusion criteria:

• Any member in the family is using a potassium-sparing diuretic
• Any member in the family is using a potassium supplement
• Any member in the family has serious renal impairment
• Any member in the family over 18 could not sign informed consent
• Life expectancy of any member in the family is shorter than 6 months in doctor's opinion