Hydration for Health Hub
Evaluating Hydration Status
How can you know how much liquid is enough for healthy hydration?
Most adults know the value of daily water intake. They also realize that water is important to good health. Indeed, epidemiological and laboratory studies show that daily water intake (and the lack of adequate hydration) influences cells, organs, and the risk of various diseases.1-3
However, adults rarely know how much to drink each day, or how to determine if they are adequately hydrated. This is unfortunate, because (1) professional organizations have published guidelines regarding the amount of water that children and adults should consume each day, and (2) it is simple to check personal hydration status.
First, despite the importance of water consumption, there is confusion among the general public and health care providers regarding the amount of water that should be consumed.4 To rectify this situation, scientific recommendations have been published by the European Food Safety Authority.5 Named “Adequate Intakes”, these recommended volumes (a) take into account intakes reported in research studies, and differences between individuals; (b) prevent deleterious effects of dehydration in the vast majority of individuals.
Table 1. Adequate intake of fluid.
Table 1 provides the Adequate Intake of fluid for various groups (EFSA, Italy). These values refer to total daily water intake from drinking water, beverages of all kinds, and from food moisture; they apply to conditions of moderate environmental temperature and moderate physical activity.
To estimate your total daily fluid intake per day, record the total volume of water plus beverages that you drink in one day. Next, add 0.6 L to this value (Armstrong, unpublished observations).
Sample Calculation. Using food labels and measuring cups, you determine your water and beverage intake for one day: 200 ml water + 300 ml milk + 200 ml fruit juice + 250 ml tea + 250 ml water + 300 ml water + 300 ml tea + 200 ml water. The total volume of these items is 2.0 liters (2,000 ml); this represents your total for water + beverages. To estimate your total daily fluid intake, add 0.6 liter (600 ml), to account for food moisture. Therefore, your total daily fluid intake (beverages + food moisture) was 2.6 liters (2,600 ml) on this day. Table 1 above presents recommendations for total daily fluid intake.
Second, any adult can check his/her hydration state. Numerous methods exist, but some are complex and require sophisticated instruments or laboratory expertise (e.g., analysis of blood and urine osmolality). The most useful methods are simple, portable and inexpensive. A review of 12 hydration assessment techniques 6 determined that three methods meet these criteria: measurements of body weight change, urine volume, and urine color. Table 2 provides information about each.
Table 2. Methods for measuring hydration state.
I personally recommend the third method: urine color. It is inexpensive, requires little time or technical expertise, and can be done by simply checking urine color during elimination. Although urine color usually is not used in hospitals or research laboratories (i.e., because it is not as precise as other laboratory methods), it is a useful field-expedient technique. Previous research has shown that urine color is strongly correlated with two internationally-recognized biomarkers: urine osmolality and specific gravity.7
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You can request a urine color chart on this H4H web site. Or, you can simply remember (1) your urine color should be similar to the color of straw, or a “pale yellow”, and (2) if urine color is dark, you should consume more water and beverages throughout the day. |
| The opinions outlined in this blog are those of the author, Prof. Lawrence E. Armstrong, and not those of the University of Connecticut. |
- Sawka MN, Cheuvront SN, Carter R. Human water needs. Nutrition Reviews 63:S30–S39, 2005.
- Institute of Medicine, National Academy of Sciences. In: “Dietary Reference Intakes for Water, Potassium, Sodium, Chloride and Sulfate.” Washington, DC: National Academies Press, pp 73-185. 2004.
- Lang F, et al. Functional Significance of Cell Volume Regulatory Mechanisms. Physiological Reviews 78(1): 247-306, 1998.
- Valtin H. ''Drink at least eight glasses of water a day.'' Really? Is there scientific evidence for ''8 × 8''? American Journal of Physiology 283(5): R993-R1004, 2002.
- European Food Safety Authority, Panel on Dietetic Products, Nutrition, and Allergies. Scientific Opinion on Dietary Reference Values for water. EFSA Journal 8(3):1459-1507, 2010.
- Armstrong, L.E. Assessing hydration status: The elusive gold standard. Journal of the American College of Nutrition 26(5): 575S-584S, 2007.
- Armstrong LE, Maresh CM, Castellani JW, Bergeron MF, Kenefick RW, LaGasse KE, Riebe D: Urinary Indices of Hydration Status. International Journal of Sport Nutrition 4:265–279, 1994.
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I think at the moment scientific recommendations for fluid intake are confusing for the public. The FSA recommends a daily amount of drinking water, EFSA and the IOM recommend an Adequate Intake (which differ from each other) and the WHO recommends a volume of water required for hydration. I doubt that many people would take the time to measure their estimated fluid intake. Furthermore, many people are still confused as to whether fluid intake includes beverages such as tea and coffee. As each individual has their own fluid intake requirements maybe it would be of greater benefit to emphasize the necessity of checking regularly for dehydration, such as looking at urine colour, and increasing fluid input if required rather than giving a fluid intake recommendation (one size fits all)?
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March 14th, 2012 - 12:17