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Recommendations for Water, Sodium and Potassium

"8 Glasses a Day" is a Myth

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Updated February 06, 2008

Athletes and water intake
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It is a myth that you need eight glasses of water a day. According to a report from researchers at the Institute of Medicine and Canadian scientists we should be more concerned about our sodium and potassium intake. Their findings indicate that most people get adequate fluids by drinking when they’re thirsty. However, we consume too much sodium and too little potassium.

Report Sets Dietary Intake Levels for Water, Salt, and Potassium

WASHINGTON -- The vast majority of healthy people adequately meet their daily hydration needs by letting thirst be their guide, says the newest report on nutrient recommendations from the Institute of Medicine of the National Academies. The report set general recommendations for water intake based on detailed national data, which showed that women who appear to be adequately hydrated consume an average of approximately 2.7 liters (91 ounces) of total water -- from all beverages and foods -- each day, and men average approximately 3.7 liters (125 ounces) daily. These values represent adequate intake levels, the panel said; those who are very physically active or who live in hot climates may need to consume more water. About 80 percent of people's total water comes from drinking water and beverages -- including caffeinated beverages -- and the other 20 percent is derived from food.

We don't offer any rule of thumb based on how many glasses of water people should drink each day because our hydration needs can be met through a variety of sources in addition to drinking water, said Lawrence Appel, chair of the panel that wrote the report and professor of medicine, epidemiology, and international health, Johns Hopkins University, Baltimore. While drinking water is a frequent choice for hydration, people also get water from juice, milk, coffee, tea, soda, fruits, vegetables, and other foods and beverages as well. Moreover, we concluded that on a daily basis, people get adequate amounts of water from normal drinking behavior -- consumption of beverages at meals and in other social situations -- and by letting their thirst guide them.

Regarding salt, healthy 19- to 50-year-old adults should consume 1.5 grams of sodium and 2.3 grams of chloride each day -- or 3.8 grams of salt -- to replace the amount lost daily on average through perspiration and to achieve a diet that provides sufficient amounts of other essential nutrients. Elevated blood pressure, which may lead to stroke, coronary heart disease, and kidney disease, is associated with sodium intake. On average, blood pressure rises progressively as salt intake increases. A tolerable upper intake level (UL) -- a maximum amount that people should not exceed -- is set at 5.8 grams of salt (2.3 grams of sodium) per day. Older individuals, African Americans, and people with chronic diseases including hypertension, diabetes, and kidney disease are especially sensitive to the blood pressure-raising effects of salt and should consume less than the UL. More than 95 percent of American men and 90 percent of Canadian men ages 31 to 50, and 75 percent of American women and 50 percent of Canadian women in this age range regularly consume salt in excess of the UL.

To lower blood pressure, blunt the effects of salt, and reduce the risk of kidney stones and bone loss, adults should consume 4.7 grams of potassium per day. However, most American women 31 to 50 years old consume no more than half of the recommended amount of potassium, and men's intake is only moderately higher. Canadians typically eat more potassium than their American counterparts. African Americans in the United States generally get less potassium than non-Hispanic whites, and because they have a higher prevalence of elevated blood pressure, increased potassium intake may have particularly significant benefits for them.

The typical Western diet is high in salt and low in potassium -- the opposite of what evidence shows is optimal for good health and reducing the risks of chronic disease, the report says. Research is needed to find ways to help people select better food choices to reduce their salt intake and boost their potassium consumption, Appel said. In addition, because Americans and Canadians get the majority of their salt -- 77 percent, according to one study -- from prepared and processed foods, research should be done to help food processors develop alternative technologies that can reduce the amount of salt added during processing without impairing taste, shelf-life, or product qualities at an affordable cost.

Read the Special Recommedations for Athletes.

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