Compliance with long-term dietary salt restriction in hypertensive outpatients

Eighty hypertensive outpatients were recruited for a dietary salt restriction program to examine long-term compliance. Twenty-four-hour urine samples were collected repeatedly (7.9 +/- 2.6 times, mean +/- s.d.) during a follow-up period of 6.4 +/- 1.7 years. After initial urine collection, nutritional education was carried out by dietitians to reduce dietary salt intake to 8 g/day or less. After every urine collection, the subjects were given advice by doctors on salt restriction, if necessary. The mean 24-hour urinary salt excretion (U-NaCl) and the mean urinary salt/creatinine ratio (U-NaCl/U-Cr) varied considerably both among and within individuals. U-NaCl/U-Cr, but not U-NaCl, in females was significantly higher than that in males, and in middle-aged subjects than in young subjects. U-NaCl and U-NaCl/U-Cr tended to decrease in the summer. In spite of the repeated educational effort, neither U-NaCl nor U-NaCl/U-Cr was different in the first control samples from that in the last samples. When 57 subjects were divided into three groups according to the urinary salt excretion level, U-NaCl was consistently higher during a follow-up period in the high-salt excretion group than in the mid-salt excretion group, while U-NaCl in the low-salt excretion group was initially lower than, but finally similar to, that in the mid-salt excretion group. These results suggest that: (1) multiple 24-hour urine samplings are required to assess urinary salt excretion in individuals; (2) the influence of age and sex should be taken into account in interpreting U-NaCl/U-Cr; and (3) it seems difficult to achieve long-term dietary salt restriction as a non-pharmacologic treatment of hypertension in an outpatient clinic.