Is low salt dietary advice a useful therapy in hypertensive patients with poorly controlled blood pressure?

In order to decide whether or not to advise a low Na trial routinely in a hypertension clinic, a randomised controlled 'management' trial was conducted to assess dietary compliance, well-being and changes in antihypertensive medication as a result of such a diet. Sixty-five out-patients on drug treatment for hypertension but with diastolic blood pressures greater than 95 mm Hg on two successive occasions were randomly allocated either to an index group on a 1 g Na (44 mmol) daily diet or to a reference group. Dietary advice was given in detail and repeated as necessary to ensure there was no misunderstanding. After three months 28% of the index group still added salt to their cooking and 13% sometimes added salt at the table. The difference between the groups in 24-hour Na excretion averaged 59 mmol at the end of the trial but 55% of the index group had a 24-hour Na excretion greater than 80 mmol. The average blood pressure at the end of the trial was only a 4 mm Hg systolic and 3 mm Hg diastolic lower in the index group. However, this modest benefit was achieved without any obvious deterioration in the quality of the lives of the patients on the low Na diet. The index group enjoyed their food as much as before and tended to require less drug treatment. On the debit side the index group complained more of transient unsteadiness (p less than 0.05) suggestive of postural hypotension. Low salt dietary advice is only marginally effective in patients poorly controlled on drug treatment. Non-compliance limits the usefulness of the advice.