Prediction of response to sodium intervention for blood pressure control.

In the Dietary Intervention Study of Hypertension (DISH) we found that patients formerly treated with drugs and assigned to sodium-reduction intervention were twice as likely to remain off medication for up to 56 weeks as were the controls assigned to no-diet intervention, after adjusting for covariates. Within the sodium-restriction group approximately 60% of 131 people were Intervention Successes (IS) (urinary sodium less than or equal to 100 mmol/day at 8 weeks). The rest were classed as Non-Intervention Successes (NIS). Of the IS group, 54% were responders (drug-free for at least 56 weeks), but about 56% of the NIS group also remained drug-free. Multiple logistics showed that no one factor was able to predict response among the IS. We conclude that the IS likely to respond to sodium reduction are not readily identifiable a priori. Furthermore, since both IS and NIS showed similar blood-pressure effects from the sodium-restriction regimen compared with controls, the questions arise: whether a factor other than sodium reduction affects the blood pressure response for the sodium-restriction group; or whether the measurement of sodium intake and excretion is sufficiently precise to distinguish compliers from non-compliers.