Drinking water is crucial to staying healthy and maintaining the function of every system in your body, including your heart, brain, digestion and muscles. Water acts a lubricant, shock absorber, building material and solvent. Water is essential for body temperature regulation through sweat, nutrient transport, waste product removal, and maintaining fluid balance. In the summer when it is hot and people sweat more, they often don’t get enough fluids. Air travel also negatively effects hydration status due to low humidity levels in the airplane cabin.
Elderly populations are at a higher risk of dehydration as a result of physiological changes and age-related decline in fluid intake. Children are also at a higher risk of dehydration as they have increased heat gain from the environment. This is due to greater surface area-body mass ratio compared to adults, increased heat production during exercise, decreased ability to dissipate heat via sweat, and decreased sensation of thirst compared to adults. Pregnant and lactating women require additional fluid intakes to avoid dehydration, as well.
Clothing, equipment and larger body size can increase sweat rate and thus dehydration risk, along with environmental conditions such as hot, humid environments and altitude. Furthermore, athletes may be more prone to dehydration during the beginning of training season. However, repeated exercise in hot environments helps the body adapt to heat stress and will result in greater sweat volume, lower electrolyte concentration of sweat, and lower temperature for onset of sweat.
Thirst may not be a reliable indicator for fluid needs and those with great sweat losses may not voluntarily drink enough fluid to adequately rehydrate. Therefore, a systematic approach to fluid replacement is necessary. For every pound of weight lost with exercise, a pint of fluid is required for replenishment (Essentials of Strength and Conditioning). Fluid guidelines differ for children and adults. The recommended water Adequate Intake is 3.7 L (125.1 oz) for men and 2.7L (91.3 oz) for women per day (Food and Nutrition Board, Institute of Medicine, National Academies). During activity, children weighing ~88 pounds should drink 5 oz cold water or flavored salted drink every 20 min during the event whether they are thirsty or not (American Academy of Pediatrics). All sources of fluid (coffee, tea, juice, soda, food fluid, etc) contribute to meeting a person’s water needs.
During exercise, sweat output can’t keep up with increases in core body temperature unless fluids are consumed. Sweat losses that exceed fluid intake can quickly lead to a hypohydrated state with subsequent increase in body temperature, decrease in blood plasma volume, and increase in heart rate and perceived exertion. Mild dehydration can greatly affect performance, resulting in increased fatigue, decreased motivation, neuromuscular control, accuracy, power, strength, muscular endurance, and overall function.
All electrolytes, including sodium chloride, potassium, magnesium and calcium, are essential to muscle contraction and nerve conduction. Increased loss of electrolytes with significant sweat production could alter performance. When large quantities of hypotonic fluid are consumed, lots of urine is produced long before the person is hydrated. Likewise, athletes who exercise intensely or for many hours and hydrate with only water or a no- or low-sodium drink may dilute their blood sodium levels to dangerously low levels, called hyponatremia. Hyponatremia leads to intracellular swelling and the athlete may present with HA, nausea, vomiting, muscle cramps, swollen hands and feet, restlessness, and disorientation. Some athletes need to replace sodium losses with higher-sodium foods and add electrolytes to drinks. Fluid intake shouldn’t exceed sweat losses to avoid hyponatremia (for example, athletes should not weigh more after workout).
Article written by Dr. Jessica Khani, PT, DPT, CSCS
The information provided is not medical advice and is not intended to be used in place of seeking advice from a professional.
Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2002/2005) and Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate (2005). National Academies.
American Academy of Pediatrics, Committee on Sports Medicine and Fitness. Sports Medicine: Health Care for Young Athletes. 2nd ed. Elk Grove Village, IL. American Academy of Pediatrics; 1991:98.
Haff, Greg. Triplett, Travis. Essentials of Strength and Conditioning. Fourth edition. Champaign, IL: Human Kinetics, 2016. Print.