The study was a single-blind randomized controlled trial conducted between February and August 2009 in two townships (Yangbajing and Gongtang) of Dangxiong County, an area at 4300 meters altitude in Tibet. A brief baseline survey and assessment for eligibility was performed before randomization. A total of 282 residents with known hypertension (systolic blood pressure ≥ 140mmHg) were recruited and randomly assigned to intervention or control with stratification by gender and baseline blood pressure. The intervention group received 6-month's supply of salt substitute (68% sodium chloride, 22% potassium chloride and 10% magnesium sulfate heptahydrate) and the control group 6-month's supply of regular salt (100% sodium chloride). After 3-month's intervention, the ones with a blood pressure above 140 mmHg / 90 mmHg will be given low-dose diuretic for further anti-hypertensive therapy. The study hypothesis is that salt-substitute will greatly reduce blood pressure in treated patients when compared to controls. Blood pressure levels were measured at baseline and followed up by trained observers using an automated sphygmomanometer and brief survey on level of compliance, amount of salt consumed, and reasons for non-compliance.

Hypertension is one of the most important risk factors that induce cardiovascular and cerebrovascular disease. Reducing the blood pressure levels of population can not only control the incidence of cardiovascular and cerebrovascular disease effectively, but also reduce the mortality. Anti-hypertension drug therapy has been proven to be an effective method to reduce blood pressure. Dietary sodium restriction and potassium supplementation is the core of dietary approaches to stop hypertension. Tibet is located on the Tibetan Plateau with an average altitude about 4000 meters above sea level. Tibetan diet is rich in meat but poor in vegetables and fruits. Salt intake is quite high due to habitual drinking of salty butter tea. Former national surveys showed a high prevalence of hypertension in Tibet. The investigators conducted this randomized controlled intervention study to test whether the investigators can offer a cost effective way to lower blood pressure and control hypertension in a sample of subjects from Yangbajing and Gongtang in Dangxiong County, Lhasa, Tibet.

A randomized controlled trial was conducted in Yangbajing Township and Gongtang Village in the Dangxiong county , Tibet. A total of 282 hypertensive patients were chosen as study subjects. The regular salt or salt substitution were randomly allocated to the two groups. The whole intervention last for 6 months, with Phase 1 for three months and a following Phase 2 for another three months. For Phase 1, the study subjects were allocated the regular salt or the salt substitute after a randomization. For Phase 2, the study subjects continued the intervention of regular salt or salt substitute while the ones with a blood pressure above 140mmHg/90 mmHg will be given low-dose diuretic for further anti-hypertensive therapy. During the whole intervention period, the study subjects were not informed of what kind of salt they were taking. Blood pressure was the major outcome and would be measured at baseline, 3 months and 6 months.

Inclusion Criteria:

• Age 40 years or older
• Resident of Yangbajing Township and Gongtang Village in Tibetan Autonomous Region, People's Republic of China
• Mean Systolic Hypertension (≥ 140 mmHg)

Exclusion Criteria:

• Currently taking any potassium supplements (or lives in household where someone does)
• Previously diagnosed kidney disease or gout (or lives in a household where someone does) and physician considered he/she cannot take salt substitute.
• Any person who intended to use salt outside the assigned treatment salt provide in the study