Salt and Heart Disease: Key Studies
The lion’s share of research on sodium and health has focused on high blood pressure, stroke, heart disease, and heart failure. The majority of these studies show that blood pressure rises with increasing amounts of sodium in the diet, and that sodium reduction lowers cardiovascular disease and death rates over the long term. Here are summaries of three key studies showing the relationship between high sodium intakes and high blood pressure, heart disease, and stroke:
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Intersalt. In the 1980s, researchers measured the amount of sodium excreted over a 24-hour period (a good stand-in for salt intake) among more than 10,000 adults from 32 countries. The average was nearly 4,000 milligrams of sodium a day. Yet the range was huge, from 200 milligrams a day among the Yanomamo people of Brazil to 10,300 milligrams in northern Japan. () The greater the salt consumption, the higher the average blood pressure and the greater the increase in blood pressure with age. Four populations—the four countries with salt intakes under 1,300 milligrams per day—had low average blood pressures and little or no upward trend of blood pressure with age.
TOHP. Two Trials of Hypertension Prevention (TOHP) were conducted in the late 1980s and early 1990s. They tested the impact of lifestyle changes on blood pressure, including weight loss, stress management, nutritional supplements, and consuming less sodium. In each of the studies, small decreases in blood pressure were seen with sodium reduction over the 18 to 36 months the trials lasted. Years after the trials had ended, the researchers surveyed the participants and found two interesting things: 1) After an average of 10–15 years, the TOHP participants in the sodium-reduction groups were 25 percent less likely to have had a heart attack or stroke, to have needed a procedure to open or bypass a cholesterol-clogged coronary artery, or to have died of cardiovascular disease. () 2) The higher the ratio of potassium to sodium in the diet, the lower the chances of developing cardiovascular trouble. () This suggests that a strategy that includes both increasing potassium and lowering sodium will be the most effective way to fight high blood pressure.
DASH. The two Dietary Approaches to Stop Hypertension (DASH) trials were major advances in blood pressure research; in both studies, Dr. Frank Sacks of the Department of Nutrition at Harvard School of Public Health played a key role, chairing the committee that designed the diet for the first trial, and then chairing the second trial. In the first DASH trial, which was completed in 1997, half of the 459 participants were assigned to a diet that emphasized fruits, vegetables, and low-fat dairy foods, and that limited red meat, saturated fats, and sweets. The other half got a standard Western diet. All of the participants’ meals were prepared by the DASH kitchen. After eight weeks, the DASH diet reduced systolic blood pressure (the top number of a blood pressure reading) by 11.4 millimeters of mercury (mm Hg) and the diastolic pressure (the bottom number of a blood pressure reading) by 5.5 mm Hg. () The second trial looked at the impact of a low-sodium DASH diet. It worked even better. Lower sodium reduced blood pressure whether it was part of the usual U.S. diet or the DASH diet. ()
References
1. Intersalt: an international study of electrolyte excretion and blood pressure. Results for 24 hour urinary sodium and potassium excretion. Intersalt Cooperative Research Group. . 1988; 297:319-28.
2. Cook NR, Cutler JA, Obarzanek E, et al. Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP). . 2007; 334:885-8.
3. Cook NR, Obarzanek E, Cutler JA, et al. Joint effects of sodium and potassium intake on subsequent cardiovascular disease: the Trials of Hypertension Prevention follow-up study. . 2009; 169:32-40.
4. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. . 1997; 336:1117-24.
5. Sacks FM, Svetkey LP, Vollmer WM, et al. Effects on blood pressure of reduced dietary sodium and the Dietary Approaches to Stop Hypertension (DASH) diet. DASH-Sodium Collaborative Research Group. . 2001; 344:3-10.
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