Among people with hypertension, switching to a low-sodium diet reduced systolic blood pressure (the top number in a reading) by five to 10 points and diastolic blood pressure (the bottom number) by two to three points, depending on race. Asians experienced the biggest decreases, followed by black people and white people.
In people with normal blood pressure, the results followed a similar pattern but the reductions were generally smaller. In white people, for instance, systolic blood pressure declined by just one point and the changes in diastolic blood pressure were negligible.
The researchers also found, however, that low-sodium diets led to small increases in hormones that cause the kidneys to hold on to salt (such as renin), and increased total cholesterol by 2.5% and triglycerides by 7%, on average.
“We know that a decrease in blood pressure would probably improve or decrease the risk of cardiovascular death but, on the other hand, an increase in [cholesterol] would increase the risk of cardiovascular death,” Dr. Graudal says. “It’s likely that these two antagonistic effects will out-balance each other, so there will be no net effect of sodium reduction on people with normal blood pressure.”
Based on the results, he says, people who eat “reasonable” amounts of sodium—which Dr. Graudal estimates at 2,400 to 3,600 milligrams per day—shouldn’t worry about eating less, but should instead focus on quitting smoking, reducing alcohol consumption if they drink excessively, and losing weight if they are too heavy. “They should focus on everything else,” he says.
Dr. Appel, however, questions the true heart risk posed by the small increases in cholesterol. If the authors’ conclusions were accurate, one could expect to see spikes in heart-attack rates in people who start low-sodium diets, but so far that has not been borne out in studies, he says.
Keith C. Ferdinand, MD, the chief scientific officer of the Association of Black Cardiologists, says a modest drop in blood pressure among people with normal blood pressure is to be expected, and shouldn’t be interpreted to mean that cutting back on sodium isn’t worthwhile.
In industrialized nations, Dr. Ferdinand says, the percentage of people with hypertension climbs steadily with age—something that doesn’t happen in parts of the world where people eat less salt. What the findings suggest, he says, is that reducing salt intake might help keep blood pressure within the normal range as people get older.
And the cholesterol increases Graudal and his team report would not be large enough to wipe out the “profound” benefits of reducing sodium intake in people with hypertension, Dr. Ferdinand says.
“This study does nothing to defer the recommendation that across the general population, sodium restriction would have a huge benefit in terms of decreasing cardiovascular disease, and perhaps lives saved,” he says.
