A new research report by Danish researchers has claimed to find some adverse consequences of dietary salt reduction primarily in persons with normal blood pressure, fueling a continuing controversy over the benefits of requiring salt reduction in foods. This comes on the eve of scheduled FDA hearings on this subject.
The new research report, by Niels A. Graudal and colleagues at the Copenhagen University Hospital and Bispebjerg University Hospital in Denmark, was published online on November 9, 2011 in the American Journal of Hypertension.
The research report, which was an analysis of 167 previously published short-term studies, found that in those studies, a reduced salt diet (to less than 2,800 milligrams of sodium per day, as compared to a group consuming more than 3,450 milligrams of sodium daily, close to the amount that the CDC says an average American eats every day) was associated with a reduction in systolic blood pressure (by less than 1% in those with normal blood pressure and by 2 – 2.5% in those with elevated blood pressure).
However, at the same time, the lower sodium intake appeared associated – at least in those with normal blood pressure – with higher levels of other hormones in the blood which reportedly could have harmful effects on heart health, if continued over a long term.
Critics have claimed the analysis was flawed, however, because it was based on studies that were too small and too short in length to accurately measure the impacts of reduced salt diets. “This is a key issue. When there is a large, abrupt reduction in sodium, it takes time to acclimate,” Lawrence Appel, MD, PhD, professor of medicine, epidemiology, and international health at Johns Hopkins Medical Institutions in Baltimore told WebMD.
Findings of the Danish Study – In More Detail
The new research report by the Danish researchers was an analysis of 167 previously published short-term studies. The Danish researchers found that in these studies, a reduced salt diet (to less than 2,800 milligrams of sodium per day, as compared to a group consuming more than 3,450 milligrams of sodium daily, which is close to the amount that the CDC says an average American eats per day) produced a cumulative average reduction in systolic blood pressure of less than 1% in Caucasians with normal blood pressure.
In the 167 studies that the researchers analyzed, those with normal blood pressure had an average age of 27 years and were studied for an average of only 7 days.
The analysis found a cumulative average reduction in systolic blood pressure of approximately 2 to 2.5% in Caucasians in the studies with elevated blood pressure (who in these studies had an average age of 51 years, and were studied for an average of 28 days).
However, the Danish researchers also found that in the group of Caucasians with normal blood pressure (average age 27, studied for an average period of 7 days), a low sodium diet also appeared associated with adverse consequences in the form of raised levels of other hormones in the blood — including plasma renin, plasma aldosterone, plasma adrenaline and plasma noradrenaline, all of which reportedly may tend to cause higher blood pressure (potentially counteracting the results of the dietary salt reduction), as well as a 2.5% higher plasma cholesterol and 7% higher level of plasma triglyceride, which reportedly could have potentially harmful effects on heart health.
In conclusion, the researchers wrote:
“In conclusion, low- vs. high-sodium diet in Caucasians with normal BP decreases BP <1%. A significant concomitant and persistent increase in plasma renin, plasma aldosterone and to a lesser degree of plasma adrenaline and plasma noradrenaline may contribute to the small effect of sodium reduction on BP. Furthermore, sodium reduction resulted in a significant increase in plasma cholesterol (2.5%) and plasma triglyceride (7%), which expressed in percentage, was numerically larger than the decrease in BP. The increase in triglyceride was numerically unchanged in studies with a duration of at least 2 weeks and in studies with sodium reduction to moderate levels of sodium intake. Due to the relatively small effects and due to the antagonistic nature of the effects (decrease in BP, increase in hormones and lipids), these results do not support that sodium reduction may have net beneficial effects in a population of Caucasians. In Caucasians with elevated BP, short-term sodium reduction decreases BP by ~2–2.5%, indicating that sodium reduction may be used as a supplementary treatment for hypertension. In Asians and blacks, the effect of sodium reduction was greater, but at present too few studies have been carried out to conclude different from that above."
The Salt Controversy
The new Danish study came out just one day before the FDA is scheduled to hold a public hearing on whether manufacturers should be required to reduce sodium content in the American food supply.
Based on other long-term studies, the New Dietary Guidelines for Americans Issued in January, 2011, by the U.S. Department of Agriculture (USDA) and Department of Health & Human Services (HHS), recommends that all Americans over age 2 persons should reduce sodium intake to less than 2,300 mg per day, and persons aged 51 years or older, blacks, and persons with hypertension, diabetes, or chronic kidney disease could benefit by reducing sodium intake to 1,500 mg per day.
Based on a long-running National Health and Nutrition Examination Survey (NHANES) study, the U.S. Centers for Disease Control & Prevention (CDC) estimates that 88.2% of the U.S. population other than the groups named above exceed the recommended daily sodium intake of <2,300 mg, and that 98% of those in the named subgroups exceed the recommended daily intake of 1,500 mg per day of sodium.
Several experts and public health authorities, including the CDC, maintain that high sodium diets are an important reason why about one-third of Americans have high blood pressure, which increases the risk of early death from conditions such as heart attacks and strokes. See e.g., Eat Less Salt & More Potassium to Live Longer, New Study Suggests. And see recommendations from the Harvard School of Public Health on cutting sodium content in your diet.
The U.S. Food & Drug Administration (FDA) currently does not regulate the amount of sodium in food. However, in recent months a movement by public health groups, including the Institute of Medicine and the American Public Health Association, and previously the American Medical Association (AMA), has called on the FDA to require food manufacturers to lower the amount of sodium they add to prepared and processed foods.
“Salt, in the amounts presently used in processed foods, is the single deadliest ingredient in the food supply, contributing to the premature deaths of tens of thousands of Americans each year,” said Michael F. Jacobson, executive director of the Center for Science in the Public Interest in a news release issued on November 1, 2011.
However, food industry representatives and some independent scientists say salt has become a scapegoat in heart disease prevention. They claim that calls to regulate salt aren’t being based on sound science.
“All the figures that you see that are associated with the benefits of salt reduction are not really benefits associated with salt reduction, they are benefits associated with blood pressure reduction,” Morton Satin, vice president of research at the Salt Institute, told WebMD.
Satin does not dispute that reducing high blood pressure is important for health. But he claims that there are better ways to do it than cutting out salt. “There is an impact of reducing salt that is beyond simple blood pressure reduction,” he says. “Using salt as the main lifestyle means of reducing blood pressure does have negative consequences, and that’s really the issue,” Satin says.
This political and economic controversy over recommendations for dietary sodium reduction has been brewing for several years between industry interests and some independent scientists vs. the majority of the health and science community. See, for example, an August 1998 report entitled “The (Political) Science of Salt,” which appeared in Science, a publication of the American Association for the Advancement of Science.
The full report of the new Danish Study is found online in the November 9, 2011 issue of the American Journal of Hypertension.
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- Diet & Nutrition: Physical Wellness;
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