Facts, Symptoms, and Signs

Signs of dehydration include thirst, irritability, general discomfort, headache, dizziness, cramps, chills, nausea, fatigue, and impaired performance.

Water constitutes more than 70% of solid tissue, including muscle. Besides oxygen, it is the most essential nutrient in the human body and plays a principal role in nearly every major bodily function. It aids in food absorption and digestion, transports nutrients and oxygen to cells, regulates body temperature, removes waste, cushions joints, and protects organs and tissues. Athletes tend to search for a “magic supplement” that will give them an advantage over their opponents. Ironically, water is the most vital “supplement,” but this simple fact is often overlooked by most athletes, 50% of whom are chronically dehydrated. They often wait until thirst induces a desire to drink, by which point they have already lost approximately 2% of their body weight, which can impair exercise performance and their ability to adapt to warm weather. A further loss of 2% to 4% of body weight can decrease their strength.

Tips for Proper Hydration

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  Prehydrate: Drink 16 to 20 oz of water 2 to 3 hours before practice or competition, and drink 8 oz of water or a sports drink 10 to 20 minutes before practice or competition.

  
  
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  Hydrate: Drink water or a sports drink regularly during practice or competition; 4 to 8 oz of fluid for every 15 to 20 minutes should be adequate, depending on the rate of sweating. Do not wait to feel thirsty before you drink.

  
  
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  Rehydrate: Drink 20 to 24 oz of water or a sports drink for every pound of lost weight.

Monitoring Hydration

Athletes should be weighed before and after each practice and competition while wearing minimal clothing. For every pound lost, approximately 24 oz (3 cups) of water or sports drinks should be consumed. Alternatively, hydration status during the day may be checked by monitoring urine color and volume. Typically, a well-hydrated athlete will urinate every 2 to 4 hours, the urine will be almost clear or the color of lemonade, and the quantity will be substantial. Conversely, a dehydrated athlete urinates fewer times per day, the urine is darker in color, akin to apple juice, and the quantity is scant.

Adequate Hydration

Dehydration is clearly preventable. Athletes should establish a drinking schedule throughout the day and be encouraged to focus on adequate consumption of fluid before, during, and after exercise. Medical staff should encourage athletes to be proactive, carry a water bottle, and drink throughout the day. A simple rule for total fluid consumption per day is calculated by dividing the athlete’s weight in half, which is the minimum amount of fluid in ounces that athletes should strive to drink daily. The following points should also be emphasized:

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  Alcoholic beverages are not included in this equation.

  
  
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  Additional fluid should be consumed on days when the athlete sweats excessively.

  
  
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  Muscle is approximately 75% water, and thus during periods of training to enhance muscle mass, additional consumption of fluid is beneficial.

Vitamin D

Adequate vitamin D levels in athletes strengthen the immune system in two ways. The vitamin D–vitamin D receptor complex appears to control lymphocyte and cytokine production, and researchers have found a link between vitamin D levels and the release of antimicrobial peptides that attack the cell membrane of pathogens. Some investigators suggest that antimicrobial peptides help fight the influenza virus and that seasonal fluctuations in vitamin D levels could explain the higher incidence of colds and flu during the winter season.

Another potential benefit of vitamin D is linked to its potential antiinflammatory properties. Intense exercise, overtraining, and other sports-related injuries are known to elevate levels of proinflammatory cytokines. Vitamin D has been shown to reduce the production of these cytokines while increasing the production of antiinflammatory cytokines. Thus it is plausible that an adequate supply of vitamin D may reduce inflammation and muscle soreness and promote quicker recovery after intense exercise.

A blood calcidiol or 25-hydroxyvitamin D [25(OH)D] level is an acceptable measure of vitamin D nutritional status ( Table 30-2 ). Optimal levels of serum 25(OH)D have not been established and are likely to vary during various phases of life. In March 2007, a group of vitamin D and nutrition researchers published an editorial contending that the desirable concentration of 25(OH)D is greater than or equal to 30 ng/mL, although it seems that a reasonable target is 50 ng/mL. Vieth et al. noted that supplemental intakes of 400 IU per day of vitamin D increase 25(OH)D concentrations by only 2.8 to 4.8 ng/mL and that daily intakes of approximately 1700 IU are needed to raise the concentration from 20 to 32 ng/mL.

Most persons obtain their daily vitamin D needs via exposure to sunlight. Ultraviolet (UV) radiation from sunlight, especially type B radiations (UVB), stimulates cutaneous production of endogenous vitamin D. However, many factors affect UV radiation exposure and vitamin D synthesis. For persons living in areas of latitudes above 35 degrees north (the latitude of Atlanta, Georgia), zero or insignificant vitamin D synthesis occurs between November and February. In persons living farther north, reduced synthesis lasts for up to 6 months. Conversely, cutaneous production of vitamin D is adequate throughout the year for persons living in areas of latitudes below 35 degrees north. Therefore athletes competing in the northern half of the United States rely on both their summer stores of vitamin D and exogenous supplementation via their diet.

Furthermore, UV energy is diminished by full cloud cover, shade, and pollution, thus reducing the synthesis of vitamin D. UVB radiation does not penetrate glass and therefore exposure to sunshine through a window does not produce vitamin D. Sunscreens also block vitamin D–producing UV rays. Furthermore, even though sunlight is critical to vitamin D synthesis, it is wise to limit exposure because UV radiation is responsible for most of the estimated 1.5 million skin cancers and 8000 deaths caused by metastatic melanoma that occur annually in the United States. Therefore it follows that the safest way to sustain adequate vitamin D levels is from consumption of fortified foods and supplements.

An inherent cause of vitamin D insufficiency is the paucity of foods that naturally contain vitamin D. Table 30-3 shows various quantities of vitamin D found in commonly consumed foods. Fish and fish liver oils are some of the best sources, and small amounts of vitamin D are found in beef liver, cheese, and egg yolks. The vitamin D in these foods is primarily in the form of vitamin D3. Some mushrooms provide vitamin D2. Most vitamin D in the diets of persons living in the United States is obtained from fortified foods. The best example is milk, most of which is fortified with vitamin D (100 IU per cup). Milk fortification was implemented in the 1930s in the United States to combat rickets. Other foods fortified with vitamin D include cereal, flours, products made from milk, and calcium-fortified fruit juices and drinks. Contrary to common belief, dairy products made from milk, such as cheese and ice cream, are generally not fortified with vitamin D. Therefore unless athletes consume oily fish frequently and drink substantial quantities of milk, their intake of vitamin D from only natural food sources can be clearly insufficient, and dietary supplements will be necessary to meet the daily needs for vitamin D.

Both vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are available as supplements. Many vegetarians may be averse to the consumption of vitamin D3 because it is manufactured from animal fat. Conversely, vitamin D2 is synthesized from plants. Athletes should be advised to choose supplements from reputable companies and to look for certifications from agencies such as United States Pharmacopeia, NSF International, or Informed-Choice. Athletes also should be advised to thoroughly evaluate all supplements prior to consumption to ensure that the supplement they use is not tainted with any substance banned by the governing body of their individual sport.

Iron

Iron has two pivotal functions. First, it transports oxygen to cells, which in turn generate energy. Second, it helps sustain peak immune system function. Consequently, these two functions are indispensable to peak athletic performance. Animal sources of iron (heme iron) are absorbed the best and can be found in beef, pork, and in the “dark meat” of chicken and turkey. On the other hand, plant sources of iron (nonheme iron) are not absorbed as readily. To improve the absorption of nonheme iron, athletes should be advised to consume foods high in vitamin C, such as citrus fruits, peppers, tomatoes, melons, berries, dark green vegetables, and juices with supplemental vitamin C. Some foods, including tea, coffee, dairy, calcium-fortified products, spinach, and nuts, can interfere with the absorption of iron. Additionally, calcium, phytates, oxalates, tannins, and polyphenols are known to inhibit iron absorption. Hence athletes who either are deficient in iron and/or are concerned about sufficient iron levels should either avoid eating the aforementioned foods or delay consumption for at least an hour after consuming foods rich in iron.