Water and Electrolytes

Water and Electrolytesby Dr. Philip Maffetone

Water may be the most common nutritional "deficiency" in the running population. This comes in the form of dehydration, even in its common mild forms. Many runners don't drink enough, and others who perform very long workouts may have a difficult time maintaining normal hydration despite drinking sufficient quantities.

The need to replace water, and the important electrolytes, is much greater than the need to replace any other nutritional substances.

A young man's body is typically 60% water, and may contain 90 pounds of water; a young woman's body may contain slightly less at 50% of her total weight. Approximately, two-thirds of this water is in the intracellular compartment of the body - predominantly within the muscles.
The feeling of thirst is activated 1.) when the total body water level is reduced, and 2.) by sodium. Even slight dehydration reduces the blood volume triggering thirst. But thirst is sensed only after dehydration is evident, making thirst a poor indicator that it's time to drink more water. Once you are dehydrated, it may take up to 48 hours to properly rehydrate using thirst as a guide.

Even mild dehydration reduces blood volume, which reduces blood flow to the muscles, organs and glands, along with oxygen and nutrients since these are also carried in the blood. The ability to expel heat is also lost since skin circulation is reduced, elevating the core temperature of the body. It is vital that runners understand the important functions of proper hydration to avoid its risks, which are amplified in warm weather.

Approximately 60% of the body's need for water comes from liquids, and 30% from foods. The other 10% is produced in the body from the cellular metabolism. Water loss at rest occurs from the kidneys (60%), from skin and lungs (totaling 30%), sweating (5%) and the large intestine (5%). During running, however, sweating increases significantly, accounting for 90% of the water lost (1-to-2 liters per hour in prolonged training or competition).

If the water lost becomes greater than the intake, blood volume diminishes with significant adverse effects. A runner may, for example, reduce his or her pace by 2% for each percent of body weight lost by dehydration. Water losses of 6-to-10% may exist in marathon events, more in longer competitions. This translates to a runner performing a 10K race in 35 minutes under normal hydration, slowing to complete the same distance in almost 38 minutes when 4% dehydrated - a significant loss of performance.

Under certain conditions, such as during hot weather, the potential for heat stroke is higher. Studies across a number of sports show that mean fluid intakes of up to one liter per hour can realistically be achieved. Therefore, consumption of this amount hourly - in small doses - may serve as a guide during long training and racing.

In athletes with high aerobic function, water regulation is more efficient, including maintenance of body temperatures and lower sweat rates. This is another reason to build a good aerobic base.
For any athlete, it is important to continually drink water everyday and not wait until an upcoming event. Ingestion of large amounts of water at one time, however, may inhibit thirst and actually promote water loss. This may result, over time, in a lower net water volume, and dehydration. The best recommendation is to consume small amount of water throughout the day, everyday. This means one or two cups each time. For most runners, a normal water intake may be between three and four liters per day as a minimum. In athletes who cross train with more total workout time, additional water may be required.

Self-assessing the need for water is important and should be done regularly. Studies have demonstrated the traditional method of assessing for hydration status, by observing the color of the urine, is a good general guide for hydration status. A definite yellow color often indicates dehydration, with a clear urine characterizing proper hydration. Most importantly, runners should learn to assess their own urine color on a daily basis and increase water as necessary. *Electrolytes. A discussion on water intake should also include electrolytes. Sodium and chloride are the dominant electrolytes, along with potassium. Electrolyte regulation is controlled by sodium and chloride, which plays a major role in regulating water. *Dietary intake of sodium, and its loss from the body help regulate both the thirst and salt appetite mechanism in the brain. This is also associated with the actions of kidney hormones which help maintain rehydration for some hours after water ingestion. As a result of this, pre-competition drinks or foods should contain moderate levels of sodium.

The adrenal hormone aldosterone is very important for electrolyte regulation - it prevents sodium and chloride loss, and rids the body of excess potassium. Adrenal stress, however, can result in excess sodium and chloride loss, and increased potassium, resulting in a diminished water volume.

A common problem in runners who have reduced aldosterone is diarrhea, which may cause further losses of sodium and water. The so-called "athlete's diarrhea" may be due to chronic adrenal dysfunction - a condition which may not be evident until the stress of competition. This is especially true in those competing in longer events. The chronic loss of sodium during adrenal dysfunction has also long been considered the reason for salt craving by many athletes.

Hyponatremia (blood sodium concentration below 136 mmol/L) can occur during or after training or racing, and can sometimes be observed even at rest in a normal blood test. Runners with low sodium do not necessarily have symptoms of hyponatremia. Early symptoms may include weakness or disorientation. In extreme cases, hyponatremia can result in such problems as rapid neurological deterioration, cardiovascular instability and seizures.

The use of sodium during competition may also be important, especially in long endurance events, as hyponatremia can occur if too much water and too little sodium is consumed. Small amounts of sodium added to water (just enough to get a very mild salt taste) can speed stomach emptying and water absorption.

I have recommended sodium tablets to many athletes for use during long endurance events. The well-hydrated runner sucks on a salt tablet until he or she loses the desire/taste for salt. In some cases, a runner may consume several salt tablets during events such as a marathon.
While large amounts of salt have been given to healthy individuals with no adverse effects, some people may be sodium sensitive. In this case, the blood pressure may rise or water retention will be evident.

With so much concern about diet and nutrition, the first step should be to assure you remain well hydrated.

Dr. Philip Maffetone practiced complementary sports medicine and applied kinesiology for over 20 years. His extensive background in biochemistry, kinesiology and exercise physiology has helped him train many world class and professional athletes. He has a doctorate degree in chiropractic and is certified in acupuncture. Athletes he has worked with include Mark Allen, Mike Pigg, Priscilla Welch and Lorraine Moller. Dr. Maffetone was named Coach of the Year in 1996 by Triathlete Magazine. His books include In Fitness and In Health and Training for Endurance (Barmore Productions). He is currently President of the MAF Group, which publishes the Maffetone Report (http://www.philsbar.com/).