Reducing Salt Intake May Reduce Blood Pressure in 3 Ethnic Groups

Laurie Barclay, MD
Charles P. Vega, MD
From Medscape Medical News

July 27, 2009 — Modestly reducing salt intake is associated with significant decreases in blood pressure in blacks, Asians and whites, according to the results of a randomized, double-blind, crossover trial reported online in the July 20 issue of Hypertension. Most previous trials were in whites, with few in blacks and Asians.

"A lower salt intake, in the long-term, could play an important role in the prevention of cardiovascular disease, renal disease and osteoporosis," lead author Feng J. He, PhD, from St. George's, University of London, United Kingdom, said in a news release. "Our study provides further support for the current public health recommendations to reduce salt intake to less than 6 grams per day."

In this crossover trial, 71 whites, 69 blacks, and 29 Asians with untreated, mildly raised blood pressure underwent salt restriction with slow sodium or placebo, each for 6 weeks. Reduction in urinary sodium levels from slow sodium to placebo was from 165 ± 58 mmol/24 hours to 110 ± 49 mmol/24 hours (9.7 - 6.5 g/day salt).

This reduction in salt intake was associated with reductions in the following measures:

•blood pressure from 146 ± 13/91 ± 8 mm Hg to 141 ± 12/88 ± 9 mm Hg (P < .001),
•urinary albumin from 10.2 (interquartile range [IQR], 6.8 - 18.9) mg/24 hours to 9.1 (IQR, 6.6 - 14.0) mg/24 hours (P < .001),
•albumin/creatinine ratio from 0.81 (IQR, 0.47 - 1.43) mg/mmol to 0.66 (IQR, 0.44 - 1.22) mg/mmol (P < .001), and
•carotid-femoral pulse wave velocity from 11.5 ± 2.3 meters/second to 11.1 ± 1.9 meters/second (P < .01).
All 3 ethnic groups had significant decreases in blood pressure and urinary albumin/creatinine ratio with salt restriction, according to subgroup analysis. However, only blacks had a significant decrease in pulse wave velocity.

Based on the findings, the investigators concluded that a modest reduction in salt intake, comparable with the current public health recommendations, could cause significant reduction in blood pressure and urinary albumin levels in all 3 ethnic groups and could improve large-artery compliance.

"About 80 percent of salt intake in developed countries comes from sodium added by the food industry," said senior author Graham A. MacGregor, MD, also from St. George. "The best strategy to reduce salt intake in the population is to persuade the food industry to make a gradual and sustained reduction in the amount of salt added to food in a structured program across the whole of the food industry. This is now happening in the United Kingdom and the average salt intake has already fallen from 9.5 to 8.6 grams per day, and will continue to fall as more salt is taken out of all foods, with the saving of many lives."

Limitations of this study include relatively small sample size, particularly regarding Asians.

"Even a small reduction in blood pressure in the whole population would have a large impact on reducing the number of people suffering and/or dying from strokes, heart attacks and heart failure," Dr. MacGregor concluded.

•The World Health Organization recommends a daily salt intake of less than 5 g/day among adults.
•The current study finds that reduced salt intake improves blood pressure and urinary albumin excretion among whites, blacks, and Asians.