Low-salt diet offers key to treating stubborn high blood pressure

Medical Tribune September 2009 P9

David Brill

Cutting down on salt can dramatically lower blood pressure (BP) in patients with resistant hypertension and could offer a genuine alternative to ramping up medications, a study suggests.

American researchers found that BP dropped by 22.7/9.1 mmHg after a week of a low-salt diet compared to a high-salt diet – a magnitude roughly equivalent to adding two more drugs.

This drop came on a background of heavy medication: patients in the study were already taking an average of 3.4 antihypertensive drugs per day.

Although small – just 12 patients took part – the study has been greeted enthusiastically by experts, who are calling for a renewed focus on salt reduction for patients whose BP remains uncontrolled.

Leading hypertension expert Dr. Lawrence Appel described the results as “striking,” particularly given that all study patients were taking hydrochlorothiazide. This volume-reducing therapy might have been expected to attenuate the effects of a low-salt diet, he wrote in an accompanying editorial. [Hypertension 2009 Jul 20; Epub ahead of print]

“The data presented … strongly suggest that persons with resistant hypertension are extremely sensitive to the BP-lowering effects of sodium reduction. The observed reductions in BP were huge – roughly equivalent to adding 2 antihypertensive medications,” wrote Appel, a Professor of Medicine at Johns Hopkins University, Baltimore, US.

“Although clinicians commonly focus on the next drug (e.g. aldosterone blocking therapy) and sometimes a device (e.g. Rheos systems that stimulate carotid baroreceptors), a renewed and aggressive emphasis on lifestyle modification, specifically sodium reduction, is warranted in patients with resistant hypertension and uncontrolled BP.”

Dr. Low Lip Ping, chairman emeritus of the Singapore Heart Foundation and founding president of the Singapore Hypertension Society, said: “This small but interesting study showed that among patients with medication-resistant hypertension, salt restriction has a substantial impact on lowering blood pressure by reducing intravascular fluid retention and improving vascular function.”

“Dietary salt restriction, ideally to less than 100 mEq of sodium/24 hours, should be recommended for all patients with resistant hypertension. With a low-salt diet these patients could have their blood pressure controlled with fewer medications,” said Low, also a private practitioner at the Low Cardiology Clinic, Mount Elizabeth Medical Center.

The study is the first to demonstrate that the benefits of salt reduction extend beyond patients with just mild or moderate hypertension, according to lead author Dr. Eduardo Pimenta.

“A low-salt diet is beneficial for all patients with hypertension but in patients with resistant hypertension the effect is stronger. Before prescribing another antihypertensive medication, doctors should spend more time with their patients explaining about low-salt diets and, if possible, refer the patient to a nutritionist,” said Pimenta, now a clinical research fellow at the Endocrine Hypertension Research Center, University of Queensland School of Medicine, Brisbane, Australia. The study itself was undertaken at the University of Alabama at Birmingham, US.

Study subjects had a mean office BP of 145.8/83.9 mmHg at baseline. All were randomized to either a high- or low-salt diet for 1 week, then a 2-week washout period, followed by a final week of the opposite diet. The low- and high-salt diets provided 50 and 250 mmol of sodium per day, respectively. [Hypertension 2009 Jul 20; Epub ahead of print]

All measures of BP were reduced by the low-salt diet as compared to the high-salt diet: systolic and diastolic; office and ambulatory; and daytime, nighttime and 24-hour.

The Singapore Heart Foundation and Hypertension Society have already been promoting the message about salt reduction – especially in light of National Nutrition Survey data suggesting that nine out of 10 Singaporeans exceed the recommended sodium intake of 2,000 mg/day.

In a joint statement to mark World Hypertension Day in May this year, the societies urged “all residents in Singapore to reduce their salt intake to reduce their risk of hypertension and hypertension-related diseases.” They also called on chefs and restaurants to lower the salt content of foods, and to avoid routinely providing soy sauce unless requested by the customer.