Journal of the American College of Nutrition, Vol. 26, No. 90005, 585S-587S (2007)
Published by the American College of Nutrition
Hydration Needs throughout the Lifespan
Sheila M. Campbell, PhD, RD
Healthcare Creative, Worthington, Ohio
Address correspondence to: Sheila M Campbell, PhD, RD, 275 Longfellow Avenue, Worthington, OH 43085. E-mail: flamingo84{at}sbcglobal.net
 |
ABSTRACT
|
|---|
In 2004, the Institute of Medicine (IOM) issued a report presenting reference intake information about water, sodium, potassium, and other electrolytes for Americans and Canadians [1]. The report established, for the first time, adequate intakes (AI) for total water (from drinking water, beverages, and food) for healthy people. An AI is the recommended average daily intake level based on observed or experimentally-determined approximations or estimates of nutrient intake by a group or groups of apparently health people that are assumed to be adequate. The AI for water is based on US survey data. The recommendations about water intake are for healthy populations—they do not apply to at-risk groups.
Key words: total water intake, adequate intake, hydration, fluid and electrolyte balance, water recommendations
Key teaching points:
• Define the terms "adequate intake" and "tolerable upper limit."
• Describe populations for whom these dietary reference are appropriate.
• List two new findings about the affect of caffeine and alcohol on hydration status.
|
|
INTRODUCTION
|
|---|
"Water is the only drink for a wise man." Henry David Thoreau (1817-1862)
|
|
INTRODUCTION
|
|---|
On February 11, 2004, a noteworthy event occurred when the first official recommendation about water intake was made. The Institute of Medicine (IOM) issued a report presenting reference intake information about water, sodium, potassium, and other electrolytes for Americans and Canadians [1]. The report established, for the first time, the following guidelines for healthy people: - Adequate intakes (AI) for total water, potassium, sodium, chloride, and sulfate
- Tolerable upper intake level (UL) for sodium and chloride
This article covers information about water only.
The fact that the IOM made a recommendation about water intake is important considering that the last edition of the Recommended Dietary Allowances (RDAs) concluded it was impossible to set a water recommendation [2]. The only guideline given for healthy adults stated, "For practical purposes, 1 ml/kcal of energy expenditure can be recommended as the water requirement for adults under average conditions of energy expenditure and environmental exposure."
|
|
DEFINITIONS
|
|---|
Since the last RDAs were published in 1989, new references have been made for intake values. The new vocabulary is used in the IOM's 2004 recommendations [1]. It is necessary to know the new definitions because they are the language now used to express water and other nutrient recommendations. The new categories of dietary reference intakes, known collectively as the dietary reference intakes (DRIs), are the following: - Estimated Average Requirement (EAR)—the average daily nutrient intake level estimated to meet the requirement of half the healthy people in a particular life stage and gender group. An EAR is made on data indicating a dose-response on critical functional endpoints or criteria. Additionally, an EAR can be established when data are sufficient to show an effect on reducing risk of disease.
- Recommended Dietary Allowance (RDA)—the average daily dietary nutrient intake level sufficient to meet the nutrient requirement of 98% of healthy people in a particular life stage and gender group. The RDA for a nutrient is derived from its EAR. If an EAR cannot be established for a nutrient, neither can a corresponding RDA.
- Adequate Intake (AI)—the recommended average daily intake level based on observed or experimentally determined approximation or estimates of nutrient intake by a group (or groups) of apparently healthy people that are assumed to be adequate. An AI is established when an RDA cannot be determined.
- Tolerable Upper Intake Level (UL)—the highest average daily nutrient intake level that is likely to pose no risk of adverse health effects to almost all individuals in the general population.
|
|
WATER INTAKE RECOMMENDATIONS
|
|---|
Data supporting the IOM water intake recommendations for children and adults came from the Third National Health and Nutrition Examination Survey 1988-1994 (NHANES III). Because survey results showed that healthy people are able to quickly compensate for over- or underhydration, it was impossible to identify a single water intake level that would ensure hydration, health, and reduction of disease risk. Consequently, neither an EAR nor RDA for water could be set. A UL could not be established either. However, an AI could be established using serum osmolality and water intake data from NHANES III.
Serum Osmolality
Serum osmolality is the concentration of osmotically active particles in serum. Serum osmolality increases when water is lost (dehydration) and decreases when water is retained (overhydration). Serum osmolality, along with other parameters, is frequently used in clinical settings to assess hydration status. Although it is not a perfect indicator [3] and is rarely used in isolation to manage patients, serum osmolality, along with intake data from NHANES III, was important for setting the AI for water. Serum osmolality was nearly identical for surveyed individuals in the lowest decile of water intake compared to the highest decile. Further, mean and median data from NHANES III indicate that serum osmolality was maintained at a constant level over a wide range of water intakes.
Water Intake
Because people are able to maintain hydration status over a wide range of water intakes, the AIs for total water for children and adults are based on median intakes of total water (see Table 1). Infants exclusively fed human milk do not require supplemental water; therefore the AI for total water for infants was based on data regarding human milk consumption. The AI for older infants was based on human milk consumption plus water intake from complementary foods and other beverages. The AIs for total water for all life stage groups are provided in Table 2.
|
|
SOURCES OF WATER
|
|---|
The recommendation for daily total water intake for women is 2.7 L (91 fl oz) and 3.7 L (125 fl oz) for men. In the United States, the annual consumption of bottled water averages 26.1 gallons per person [4], or about six 8 fl oz of water daily (48 fl oz) [5]. Obviously this volume is not adequate. However, drinking water (bottled or tap) is not the only source of dietary water. Water in food provides approximately 19% of total daily water intake. Because water intake comes from drinking water, other liquids, and food, the AIs for water are for total daily water intake and include all dietary water sources. The water content of various foods is provided in Table 3 [6].
Caffeine
Contrary to popular belief, research shows that coffee, tea, and other caffeine-containing beverages do not increase urine output or negatively affect indicators of hydration status in those who are accustomed to consuming caffeine [7]. The IOM report states that "...caffeinated beverages appear to contribute to the daily total water intake similar to that contributed by non-caffeinated beverages." [1].
Alcohol
What may be even more surprising than the information about the effect of caffeinated beverages is news about the diuretic effect of alcohol. While there is increased diuresis during the initial three hours after consuming an alcoholic beverage, an anti-diuretic effect commences six hours after ingestion that can last up to 12 hours post-consumption. This effect is possibly due to vasopressin suppression [8]. Based on a review of the literature, the IOM report states "...it appears that the effect of ethanol ingestion on increasing excretion of water appears to be transient and would not result in appreciable fluid losses over a 24-hr period." [1].
|
|
CAVEATS
|
|---|
Most healthy people adequately meet their daily water needs when they let thirst be their guide. Note, however, that this is not true for athletes, military personnel in hot environments, people who are ill, elderly individuals, or infants. The sense of thirst (or the ability to communicate it) of these populations is not an adequate reflection of their water needs. The AI for water is not a suitable guide for these populations.
|
|
CONCLUSION
|
|---|
Much more research is required on hydration needs in various conditions and on water's role in promoting health and preventing disease. Some people argue about the appropriateness of data used to create the AIs for water. It is recognized that techniques to fine tune hydration assessment that can be easily used are needed. Nonetheless, the fact that an AI for water has been established is noteworthy because it provides guidance where none existed previously. To view the entire report online, visit http://www.nap.edu/catalog/10925.html.
|
|
FOOTNOTES
|
|---|
Conflict of Interest Disclosure: There are no conflicts of interest to declare in connection with this work.
Received July 16, 2007.
|
|
REFERENCES
|
|---|
- Institute of Medicine and Food and Nutrition Board:"Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate."
Washington, DC: National Academies Press,2004
.
- Subcommittee on the Tenth Edition of the Recommended Dietary Allowances, Food and Nutrition Board, Commission on Life Sciences, National Research Council: Water and electrolytes. In:"Recommended Dietary Allowances,"
10th ed. Washington, DC: National Academies Press, pp.247
–261,1989
.
- Armstrong LE: Hydration assessment techniques.Nutr Rev63(6 Pt 2)
:S40
–54,2005
.
- Beverage Marketing Corporation: Bottled Water Continues As Number 2 in 2005. New York, NY:2005
. Available at http://www.bottledwater.org/public/Stats_2005.doc.
- Bullers, AC:Bottled water: Better than the tap?
Rockville, MD: FDA,2002
. Available from: http://www.fda.gov/fdac/features/2002/402_h2o.html.
- Campbell SM: Dietary Reference Intakes: Water, potassium, sodium, chloride, and sulfate.Nutrition & the MD30
:1
–4,2004
.
- Grandjean AC, Reimers KJ, Bannick KE, Haven MC: The effect of caffeinated, non-caffeinated, caloric and non-caloric beverages on hydration.J Am Coll Nutr19
:591
–600,2000
.[Abstract/Free Full Text]
- Taivainen H, Laitinen K, Tahtela R, Kilanmaa K, Valimaki MJ: Role of plasma vasopressin in changes of water balance accompanying acute alcohol intoxication.Alcohol Clin Exp Res19
:759
–762,1995
.[Medline]
TOP
ABSTRACT
INTRODUCTION
