Follow Your Thirst, Report Says

Academy of Sciences Discounts Need for 8 Cups of Water Daily
By Sally Squires
Washington Post Staff Writer
Thursday, February 12, 2004

A report by the National Academy of Sciences yesterday rejected the widely repeated advice that people should drink eight glasses of water a day, saying that the vast majority of Americans will be amply hydrated if they simply let thirst be their guide.

Taking on another contentious dietary issue, an expert panel assembled by the academy also said that 95 percent of American men and 75 percent of women consume too much salt. To help cut rates of high blood pressure, which afflicts an estimated 90 percent of Americans as they age, the panel urged consumers to reach for more fruit, vegetables and other foods rich in potassium while drastically cutting back on processed food and other fare high in sodium.

"The lower the better for sodium; the higher the better for potassium," said Lawrence J. Appel, chairman of the panel that drafted the report for the academy's Food and Nutrition Board, and professor of medicine at Johns Hopkins University.

With 2 out of 3 adults in the United States overweight or obese, healthy eating is of increasing concern to consumers, the medical community and the federal government. Since 1943, the academy has been charged with updating recommendations for daily intake of essential nutrients, ranging from carbohydrates, fats and proteins to vitamins and minerals. The findings issued yesterday offered new recommendations for water as well as for sodium, potassium, chloride and sulfate.

Thirst is the main determinant of how much fluid people need, the report noted. On average, most adult men need about 16 cups a day of fluid and women require roughly 11 cups. National food surveys suggest that about 80 percent of daily fluid intake comes from beverages. Water in food provides the remaining 20 percent.

Where the report departs from conventional wisdom is in noting that all beverages -- including coffee, tea and even alcohol -- contribute toward meeting the daily fluid intake.

Some studies have suggested that because caffeine and alcohol can increase urine production, they actually cause water loss, the report concluded, noting that these effects "may be transient in nature." For this reason, such beverages "can contribute to total water intake," the report said, noting that "no one source is essential for physiological function and health."

Reading food labels needs to be a key strategy to reduce sodium consumption, said John Erdman Jr., chairman of the NAS standing committee that oversees the dietary recommendations.

Sodium, the main ingredient in salt, increases blood pressure. Studies have shown that in populations where sodium intake is low, blood pressure does not rise with age as it does in the United States.

The NAS report recommends that healthy 19- to 50-year-old adults consume about 1.5 grams of sodium per day. That is equal to nearly 4 grams of salt, or about two- thirds of a teaspoon of salt. Even so, committee members said that about 70 percent of sodium intake comes from processed food -- not salt added in home cooking or at the dining table.

The report for the first time also set a recommended upper limit for salt consumption, putting the figure at 5.8 grams per day. This top level should not be exceeded by older individuals, African Americans and people with such chronic ailments as high blood pressure, diabetes and kidney disease, who the NAS said "are especially sensitive to blood pressure-raising effects of salt and should consume less than the upper limit."

Experts, including Jerome D. Cohen, professor of medicine at the St. Louis University School of Medicine, praised the step, saying that "it will help us to influence food manufacturers and various food groups that need to be our allies" in lowering sodium content of food. "We can't do this alone," said Cohen, who also serves on a blood pressure advisory committee for the National Heart, Lung, and Blood Institute.

"The new intake levels may be "very challenging for most consumers to achieve," said Robert Earl, senior director of nutrition policy for the National Food Processors Association, a food industry trade group. But Earl noted that if consumers read food labels carefully, they can find "traditional, reduced, low, very low and no-sodium products. Anyone looking for sodium-modified products has a wide variety of such products available at any food store."

The latest NAS recommendations closely match similar dietary advice from the federal government, the American Heart Association and the American Public Health Association to reduce sodium-filled food and boost potassium-rich fare, such as fresh fruit and vegetables.

But they drew criticism from the Salt Institute. "There is no evidence that asking everyone to reduce dietary salt improves health outcomes," said Salt Institute President Richard L. Hanneman.

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