A total of 282 Tibetans aged 40 or older with known hypertension ( systolic BP140 mmHg ) were recruited and randomized to intervention ( salt-substitute , 65 % sodium chloride , 25 % potassium chloride and 10 % magnesium sulfate ) or control ( 100 % sodium chloride ) in a 1 : 1 allocation ratio with three months ' supply .