Dehydration - Prevention

Prevention

Dehydration is best avoided by drinking sufficient water. The greater the amount of water lost through perspiration, the more water must be consumed to replace it and avoid dehydration. Since the body cannot tolerate large deficits or excesses in total body water, consumption of water must be roughly concurrent with the loss (in other words, if one is perspiring, one should also be drinking some water frequently).

For routine activities in which a person is not perspiring to any large degree, drinking when one is thirsty is sufficient to maintain hydration. However, during exercise, relying on thirst alone may be insufficient to prevent dehydration from occurring. This is particularly true in hot environments or for those older than 65. For an exercise session, an accurate determination of how much fluid is necessary to consume during the workout can be made by performing appropriate weight measurements before and after a typical exercise session, to determine how much fluid is lost during the workout.

Drinking water beyond the needs of the body entails little risk when done in moderation, since the kidneys will efficiently remove any excess water through the urine with a large margin of safety.

A person's body, during an average day in a temperate climate such as the United Kingdom, loses approximately 2.5 litres of water. This can be through the lungs as water vapor (about 350ml), through the skin by perspiration (100ml) and by diffusion through the skin (350ml), or through the kidneys as urine (1000-2000ml, about 900ml of which is obligatory water excretion that gets rid of solutes). Some water (about 150-200ml, in the absence of diarrhea) is also lost through the bowels. In warm or humid weather or during heavy exertion, however, the water loss can increase by a factor of 10 or more through perspiration; all of which must be promptly replaced. In extreme cases, the losses may be great enough to exceed the body's ability to absorb water from the gastrointestinal tract; in these cases, it is not possible to drink enough water to stay hydrated, and the only way to avoid dehydration is to either pre-hydrate or find ways to reduce perspiration (through rest, a move to a cooler environment, etc.)

A useful rule of thumb for avoiding dehydration in hot or humid environments or during strenuous activity involves monitoring the frequency and character of urination. If one develops a full bladder at least every 3–5 hours and the urine is only lightly colored or colorless, chances are that dehydration is not occurring; if urine is deeply colored or urination occurs only after many hours or not at all, water intake may not be adequate to maintain proper hydration.

When large amounts of water are being lost through perspiration and concurrently replaced by drinking, maintaining proper electrolyte balance becomes an issue. Drinking fluids that are hypertonic or hypotonic with respect to perspiration may have grave consequences (hyponatremia or hypernatremia, principally) as the total volume of water turnover increases.

If water is being lost through mechanisms such as vomiting or diarrhea, an imbalance can develop very quickly into a medical emergency.

During sports events such as marathons, athletes take frequent water stops and water breaks to avoid dehydration. The claim that pure water without isotonic additives can prevent dehydration is questioned, however, and the European Food Safety Authority states that reduced body water content is only a symptom of dehydration and not what drinking water controls. Drinking water without replenishing electrolytes may instead lead to developing hypotonic dehydration.