This report refers to total water, which includes the water contained in beverages and the moisture in foods, to avoid confusion with drinking water only.
Total water intake at the reference level of 3.7 liters for adult men and 2.7 liters for adult women per day covers the expected needs of healthy, sedentary people in temperate climates. Temporary underconsumption of water can occur due to heat exposure, high levels of physical activity, or decreased food and fluid intake. However, on a daily basis, fluid intake driven by thirst and the habitual consumption of beverages at meals is sufficient for the average person to maintain adequate hydration
Prolonged physical activity and heat exposure will increase water losses and therefore may raise daily fluid needs. Very active individuals who are continually exposed to hot weather often have daily total water needs of six liters or more, according to several studies.
While concerns have been raised that caffeine has a diuretic effect, available evidence indicates that this effect may be transient, and there is no convincing evidence that caffeine leads to cumulative total body water deficits. Therefore, the panel concluded that when it comes to meeting daily hydration needs, caffeinated beverages can contribute as much as noncaffeinated options.
Some athletes who engage in strenuous activity and some individuals with certain psychiatric disorders occasionally drink water in excessive amounts that can be life-threatening. However, such occurrences are highly unusual. Therefore, the panel did not set a UL for water.
Additional Findings on Salt and Potassium
The recommended intake levels for salt provide enough sodium to balance losses from sweat by people who are exposed to temperatures higher than what they are used to or who are moderately physically active. Endurance athletes and other very active individuals may need more sodium because they lose more in sweat from intense and prolonged physical activity.
High salt intake has been directly linked to elevated blood pressure, also known as hypertension. About 25 percent of American adults and more than half of those age 60 and older have hypertension. American men's median intake of salt is between 7.8 and 11.8 grams per day, and women consume between 5.8 and 7.8 grams every day. Canadian men and women consume 7.1 to 9.7 grams and 5.1 to 6.4 grams per day respectively. Because these figures do not include the salt that people add at the table, they are probably underestimates.
Studies indicate that reduced consumption of salt coupled with increased potassium intake can blunt the age-related rise in blood pressure. American men consume just 2.8 to 3.3 grams of potassium daily on average, and women get an average of only 2.2 to 2.4 grams each day. Canadians consume slightly more, at 3.2 to 3.4 grams per day for men and 2.4 to 2.6 grams per day for women. Fruits and vegetables are both low in sodium and high in potassium. Among foods with the highest amounts of potassium per calorie are spinach, cantaloupes, almonds, brussels sprouts, mushrooms, bananas, oranges, grapefruits, and potatoes.
There was no evidence of chronic excess intakes in apparently healthy individuals to compel establishing a UL for potassium. However, people who have kidney dysfunctions that impair their ability to excrete potassium or who are on certain types of drug therapies -- such as ACE inhibitors -- should be under the supervision of a medical professional, who may recommend consuming less than the recommended 4.7 grams per day.
This study was sponsored by the U.S. Department of Health and Human Services' Office of Disease Prevention and Health Promotion and the National Institutes of Health; Health Canada; U.S. Environmental Protection Agency; U.S. Department of Agriculture; Institute of Medicine; the Dietary Reference Intakes Private Foundation Fund, including the Dannon Institute and the International Life Sciences Institute-North America; and the Dietary Reference Intakes Corporate Donors' Fund, contributors to which have included the Nabisco Food Group, Mead Johnson Nutritionals, and M&M Mars.
This study is one of a series undertaken by scientists from the United States and Canada under the auspices of the Institute of Medicine's Food and Nutrition Board to develop reference values for nutrients for use in both countries. The Institute of Medicine is a private, nonprofit organization that provides health policy advice under a congressional charter granted to the National Academy of Sciences.