4.2: Water

Water isn’t generally called a nutrient as such, but it’s obviously essential. We can survive months without food, but only days without water. We feel the deficiency (dehydration) immediately as thirst. The body is over half water, and water is the bodily fluid in which chemical reactions take place and in which substances are transported. Water also plays a crucial role in keeping us from overheating—we are cooled as the water in perspiration evaporates from our skin.

Table 4-1: Essential nutrients

How much water we need depends on our activities, the weather, etc., but our body is adept in balancing the amount we use with the amount we take in. Under normal conditions, adults need about 1 to 1½ quarts of water per 1,000 calories used, e.g., 2-3 quarts/day for someone who uses 2,000 calories/day. But we don’t need to drink this much water or beverages. We get a lot of water in food (e.g., note how much water is absorbed by rice as it cooks, or how much smaller a dried apricot is than a fresh one). We also get water as a byproduct of some chemical reactions in the body.

If we take in more than we need, we urinate more. If we use more than we take in, we get thirsty. But thirst isn’t a reliable gauge of water need when lots of water is lost fast, as in severe diarrhea or vomiting, or in profuse sweat loss from strenuous exercise in hot weather. Also, the thirst mechanism doesn’t work as well in older adults. In such cases, one should make a point of drinking enough water. Urine is normally light yellow, so a change to a deeper yellow typically indicates a need to drink more water.

Athletes need to drink plenty of water to prevent dehydration. Dehydration interferes with performance—and can lead to heat stroke. In hot weather, sweat loss that occurs in endurance events can be so large that athletes can’t drink and absorb water fast enough to keep pace with their need.

For events longer than a half-hour, athletes should drink water before, during, and after the event, even if they aren’t thirsty. Cold water may be preferable because it’s absorbed a little faster, and is itself cooling. But unchilled water is fine.

Don’t overdo the water. Drinking water beyond what’s needed to replace water loss during an event can dilute the sodium in blood to dangerously low levels. At the 2002 Boston Marathon, 488 runners provided a blood sample afterwards; 62 of them (13%) had water overload. A local 28-year-old participant’s death after this race was linked to excessive water intake.

In endurance events of more than 90 minutes, beverages of 6 to 8% carbohydrate (glucose, sucrose, or glucose polymer), starting about 30 minutes before fatigue sets in, can enhance performance. Most commercial sports drinks have this amount.

To make a sports drink of 7% carbohydrate,* add 1/3 cup table sugar (sucrose) per quart of water. A bit of unsweetened Kool-Aid adds flavor and color. A bit of sodium can help speed absorption of the sugar and water. Adding 1/8 teaspoon of table salt (sodium chloride) per quart provides about 70 mg sodium per cup.

Taking sodium or other minerals isn’t generally necessary. Loss of sodium and other minerals in sweat is small and doesn’t compromise performance, except in extreme circumstances. (Add sodium to drinking water in endurance events of more than 4 hours; sweat loss is large and prolonged.) Following the event, the lost minerals are readily replenished by a normal diet.

Many people take various amino acids, vitamins, etc., to enhance athletic performance, but most get their information from those selling them. The Office of Dietary Supplements provides science-based information on the safety and effectiveness of various supplements. ods.od.nih.gov/factsheets/ExerciseAndAthleticPerformanceHealthProfessional/

^{*Diluting some fruit juices with an equal part of water can also give you a 7% carbo drink. Undiluted apple juice, for example, is about 13% carbohydrate.}