March 9, 2001

By Eleanor Gilman

Skipper Chong Warson

here is a well-publicized link between excess salt and hypertension, or high blood pressure. But did you know that consuming too much salt can increase your risk for other diseases as well?

"High-salt diets can cause a lot of health problems," explains Jiang He, M.D., Ph.D., associate professor of epidemiology at the Tulane University School of Public Health and Tropical Medicine. High-salt diets can increase the risk of a variety of conditions, including stomach cancer, cataracts, and osteoporosis. "It damages parts of the body through different mechanisms, but salt tastes good, so people in modern society eat a lot of it," explains Dr. He.

Salt and stomach cancer

Diets high in salt are thought to increase the risk of stomach cancer, according to researchers at the American Institute for Cancer Research, which reviewed 17 studies analyzing salt consumption.

"Excess salt destroys many of the cells lining the stomach. When these cells are replaced, excessive cell division increases the risk of cancer," says Pelayo Correa, M.D., Boyd Professor of Pathology at Louisiana State University. "Salt can also play a role in the prevalence of gastritis associated with Helicobacter pylori, a source of infection that may result in stomach cancer."

Packaged food found in the aisles of American grocery stores may contain as much as salt as foods commonly found in Portugal, Japan, and parts of China and Latin America -- where salt-preserved foods are most popular and stomach cancer rates are the highest. "The higher the salt intake, the higher the risk for stomach cancer," explains Dr. Correa. "When people reduce their salt intake, their risk of stomach cancer drops."

Salt and cataracts

A clear relationship also exists between high salt intake and posterior subcapsular cataract, the most serious type of cataract among older people. Australian researchers who studied nearly 3,000 people found that those who consumed the most salt -- an average of 3,164 milligrams per day -- had approximately twice the risk of this disabling condition as did those with the lowest intake of salt intake -- an average of 1,273 milligrams per day.

"Higher sodium levels in the blood could interfere with the level of sodium inside the lens," explains Robert G. Cumming, M.D., Ph.D., associate professor of epidemiology at the University of Sydney and lead author of the study.

The Australian study supports the findings of both an human study that found an association between high sodium intake and increased risk of cataract extraction, and an animal study that showed that high sodium intake caused cataract formation. Sodium restriction in the animals led to the reversal of early cataracts.

Most people eat more salt than the recommended daily allowance of 2,400 milligrams. In fact, average salt intake is around 20 times as much as our bodies require.

Given that cataracts are the leading cause of blindness worldwide, it seems prudent to consider the Australian researchers' suggestion that a reduction in salt consumption may help prevent cataracts in older adults.

Salt and osteoporosis

Yet another relationship has been noticed between salt intake and osteoporosis. Studies on both humans and animals have shown that excess salt intake increases the loss of calcium through the urine. "Every 2,300 milligrams of sodium excreted by the kidney pulls 20 to 60 milligrams of calcium out with it," says Randi Wolf, Ph.D., epidemiologist and research assistant professor at Columbia University. That's bad because "the calcium that shows up in urine comes from breakdown of bone," says Wolf.

If calcium intake is adequate, the body can compensate for higher sodium intake by increasing absorption of calcium from the gastrointestinal tract. But if you lose more calcium than you take in, your body leeches calcium from your bones, increasing your risk for osteoporosis.

"If you stick to the recommended intake of sodium (no more than 2,400 milligrams per day) and consume adequate calcium (1,200 milligrams per day for people over 50), you will probably be protected," says Dr. Wolf. "But if you consume more than the recommended sodium intake, you may need to up your calcium consumption."

The obesity factor

Since high blood pressure is a strong risk factor for coronary heart disease and stroke, it makes sense that a high-salt diet, implicated in high blood pressure, increases the risk of cardiovascular disease. For those who are overweight, a high-salt diet can be especially dangerous, according to Tulane University researchers. They found that high sodium intake is significantly associated with increased stroke incidence and with death from stroke, coronary heart disease, and cardiovascular disease in people who are overweight. The long-term study involved 14,000 participants over a 19-year period.

"Overweight people retain more sodium and are more sensitive to the effect of sodium on blood pressure," says Dr. He, lead author of the study.

Researchers say they are troubled by the prevalence of obesity in the United States; they recommend that overweight patients lose weight and reduce sodium intake. "But people who have trouble losing weight can lessen their risk of cardiovascular disease by reducing their salt intake," says Dr. He. "Reducing sodium by about 6 grams [6,000 milligrams] a day could reduce mortality from stroke by 47 percent and heart attack by 31 percent."

Salt and your diet

Most people eat more salt than the recommended daily allowance of 2,400 milligrams. In fact, average salt intake is around 20 times as much as our body requires.

Where does the excess salt in our diet come from? Foods in their natural state contain little salt. Most salt people consume comes from manufactured foods -- like breakfast cereals, rice mixes, and processed meat. Twenty to 30 percent of salt is added during cooking or while eating.

Reports from experts concerned with diet and cardiovascular disease or diet and chronic diseases find that lower salt consumption is best; only two out of 70 United States experts who have recently studied the issue disagree. But until food manufacturers are persuaded to lower the salt content in their products, it's up to consumers to be cautious about their salt intake.

Related link:

• Outside link: American Dietetic Association

Send feedback on this article.