People who have uncontrolled high blood pressure despite taking multiple blood pressure-lowering drugs can lower their blood pressure by adopting a low-salt diet, according to a study released today at the American Heart Association’s 62nd Annual Fall Conference of the Council for High Blood Pressure Research in Atlanta.

“A high-salt diet contributes importantly to treatment-resistant hypertension (high blood pressure),” Dr. Eduardo Pimenta from the Dante Pazzanese Institute of Cardiology, Sao Paulo, Brazil, told Reuters Health.

Pimenta and colleagues measured the impact of a restricted-salt diet on 24-hour blood pressure readings, obtained using a recorder worn continuously for 24 hours, in 13 adults with treatment-resistant hypertension. In a “crossover” study, low- and high-salt diets were tested for seven days separated by a two-week “washout” period, after which the subjects switched groups.

The patients were taking an average of 3.6 blood pressure lowering medications and had an average “office” blood pressure of 147.9 over 85.2 millimeters of mercury (mmHg). Normal blood pressure is 140 over 90 mmHg.

According to Pimenta and colleagues, the amount of sodium excreted in urine over 24-hours was markedly reduced during the low-salt diet compared to the high-salt diet.

Moreover, on the low-salt diet, systolic blood pressure—the top number in blood pressure readings that represent pressure while the heart contracts - was reduced by 22.6 mmHg, while diastolic blood pressure - the bottom number that gives the pressure when the heart relaxes between beats - was lower by 9.2 mmHg.

“We were expecting blood pressure reduction with low-salt diet but the reduction was larger than we expected,” Pimenta admitted.

The study also confirms that a high-salt diet can impair blood vessel function and cause people to retain fluid “despite diuretic therapy,” Pimenta said. During the low-salt diet, healthy reductions in the fluid volume were seen.

This research, the study team concludes, clearly demonstrates the harmful effects of a high-salt diet in people with stubborn hypertension, as well as the benefits of a low-salt diet.

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