Who’s at high risk of developing health problems related to salt consumption?
- People over age 50
- People who have high or slightly elevated blood pressure
- People who have diabetes
- African Americans
What happens to my body if I eat too much sodium?
In most people, the kidneys have trouble keeping up with the excess sodium in the bloodstream. As sodium accumulates, the body holds onto water to dilute the sodium. This increases both the amount of fluid surrounding cells and the volume of blood in the bloodstream. Increased blood volume means more work for the heart and more pressure on blood vessels. Over time, the extra work and pressure can stiffen blood vessels, leading to high blood pressure, heart attack, and stroke. It can also lead to heart failure. There is also some evidence that too much salt can damage the heart, aorta, and kidneys without increasing blood pressure, and that it may be bad for bones, too.
High blood pressure is a leading cause of cardiovascular disease. It accounts for two-thirds of all strokes and half of heart disease. (1) In China, high blood pressure is the leading cause of preventable death, responsible for more than one million deaths a year. (2)
The importance of potassium
Sodium and potassium have opposite effects on heart health: High salt intake increases blood pressure, which can lead to heart disease, while high potassium intake can help relax blood vessels and excrete the sodium and decrease blood pressure.
Our bodies need far more potassium than sodium each day, but the typical US diet is just the opposite: Americans average about 3,300 milligrams of sodium per day, about 75 percent of which comes from processed foods, while only getting about 2,900 milligrams of potassium each day. (3,4)
A recent study in Archives of Internal Medicine provides more evidence that high salt diets have negative effects on health, and found that:
- People who eat high sodium, low potassium diets have a higher risk of dying a heart attack or from any cause.
- People can make a key dietary change to help lower their risk: Eat more fresh vegetables and fruits, which are naturally high in potassium and low in sodium—and eat less bread, cheese, and processed meat, as these and other processed foods are high in sodium and low in potassium. (5)
In this study, people with the highest sodium intakes had a 20 percent higher risk of death from any cause than people with the lowest sodium intakes. People with the highest potassium intakes had a 20 percent lower risk of dying than people with the lowest intakes. But what may be even more important for health is the relationship of sodium to potassium in the diet: People with the highest ratio of sodium to potassium in their diets had double the risk of dying of a heart attack than people with the lowest ratio, and they had a 50 percent higher risk of death from any cause. (5)
Cardiovascular disease
Besides contributing to high blood pressure, consuming high amounts of sodium can also lead to stroke, heart disease, and heart failure.
Research also shows that reducing sodium lowers cardiovascular disease and death rates over the long term. (6)
3 key studies about sodium and cardiovascular disease:
1. 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. (7) Populations with higher salt consumption had higher average blood pressures and greater increases of blood pressures with age. Four groups of people—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.
2. 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 that:
- 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. (8)
- The higher the ratio of potassium to sodium in a participant’s diet, the lower the chances were of developing cardiovascular trouble. (9) This suggests that a strategy that includes both increasing potassium and lowering sodium may be the most effective way to fight high blood pressure.
3. DASH: The Dietary Approaches to Stop Hypertension (DASH) trials, begun in 1994, were major advances in blood pressure research, demonstrating the links between diet and blood pressure. (11) In the first study, 459 participants were randomly assigned to either a standard American diet high in red meat and sugars, and low in fiber; a similar diet that was richer in fruits and vegetables; or the “DASH diet,” which emphasized fruits, vegetables and low-fat dairy foods, and limited red meat, saturated fats, and sweets. After eight weeks, both non-control diets reduced systolic (the top number of a blood pressure reading) and diastolic (the bottom number of a blood pressure reading) blood pressure, with the DASH diet producing a stronger effect.
The second study found that lowering sodium in either the DASH or standard American diet had an even stronger impact on reducing blood pressure. The DASH study contributed much of the scientific basis for the Dietary Guidelines for Americans 2010, which recommends reducing daily sodium to less than a teaspoon.
Other diseases
Cancer
Research shows that higher intake of salt, sodium, or salty foods is linked to an increase in stomach cancer. The World Cancer Research Fund and American Institute for Cancer Research concluded that salt, as well as salted and salty foods, are a “probable cause of stomach cancer.” (12)
Osteoporosis
The amount of calcium that your body loses via urination increases with the amount of salt you eat. If calcium is in short supply in the blood, it can be leached out of the bones. So, a diet high in sodium could have an additional unwanted effect—the bone-thinning disease known as osteoporosis. (1) A study in post-menopausal women showed that the loss of hip bone density over two years was related to the 24-hour urinary sodium excretion at the start of the study, and that the connection with bone loss was as strong as that for calcium intake. (13) Other studies have shown that reducing salt intake causes a positive calcium balance, suggesting that reducing salt intakecould slow the loss of calcium from bone that occurs with aging.
References
1. He FJ, MacGregor GA. A comprehensive review on salt and health and current experience of worldwide salt reduction programmes. J Hum Hypertens. 2009;23:363-84.
2. He J, Gu D, Chen J, et al. Premature deaths attributable to blood pressure in China: a prospective cohort study. Lancet. 2009;374:1765-72.
3. Brown IJ, Tzoulaki I, Candeias V, Elliott P. Salt intakes around the world: implications for public health. Int J Epidemiol. 2009;38:791-813.
4. Dietary Guidelines for Americans Scientific Advisory Committee. Report of the Dietary Guidelines Advisory Committee on the Dietary Guidelines for Americans, 2010, to the Secretary of Agriculture and the Secretary of Health and Human Service. 2010.
5. Yang Q, Liu T, Kuklina EV, et al. Sodium and potassium intake and mortality among US adults: prospective data from the Third National Health and Nutrition Examination Survey. Arch Intern Med. 2011;171:1183-91.
6. Strazzullo P, D’Elia L, Kandala NB, Cappuccio FP. Salt intake, stroke, and cardiovascular disease: meta-analysis of prospective studies. BMJ. 2009;339:b4567.
7. Institute of Medicine. A Population-Based Policy and Systems Change Approach to Prevent and Control Hypertension. Washington, D.C.: The National Academies Press; 2010.
8. 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). BMJ. 2007;334:885-8.
9. 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. Arch Intern Med. 2009;169:32-40.
10. Appel LJ, Moore TJ, Obarzanek E, et al. A clinical trial of the effects of dietary patterns on blood pressure. DASH Collaborative Research Group. N Engl J Med. 1997;336:1117-24.
11. 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. N Engl J Med. 2001;344:3-10.
12. World Cancer Research Fund, American Institute for Cancer Research. Food, Nutrition, Physical Activity, and the Prevention of Cancer: A Global Perspective. London; 2007.
13. Devine A, Criddle RA, Dick IM, Kerr DA, Prince RL. A longitudinal study of the effect of sodium and calcium intakes on regional bone density in postmenopausal women. Am J Clin Nutr. 1995;62:740-5.
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