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Stay Hydrated in the Heat

By Deb Iovoli, MS,RDN,CSSD,LDN

It’s summertime! This time of year brings heat and humidity and the need to consume more fluids on a daily basis, especially when running or exercising. Dehydration certainly affects our training and racing performance. As little as two percent of body weight lost in fluids can impair performance.

Fluid balance is vital to normal cardiovascular and thermoregulatory functions (body temperature).  Dehydration increases the risk of other heat illnesses, too, such as heat exhaustion and life-threatening heatstroke, especially in hot, humid weather or higher altitudes. Mild dehydration over time has been linked with increased cancer risk, reduced salivary gland function, kidney stones, and even fatal heart attacks.

The major cause of dehydration in athletes is sweat loss that is not compensated for through proper fluid intake. Each athlete has different rates of sweat loss because that loss is based on environmental conditions, clothing type, equipment worn, metabolic rate, and the athlete’s body surface area. Higher body mass will put an athlete at greater risk for dehydration.

Thirst is the first symptom of dehydration but you should consume fluids before you feel thirsty. Other symptoms of dehydration include:

  • Excessive thirst
  • Fatigue
  • Muscle weakness
  • Headache
  • Dizziness
  • Dry mouth, lips, and skin
  • No urination or a small amount of dark yellow urine*
  • Lightheadedness
  • Increased body temperature
  • Nausea
  • Constipation
  • Labored breathing

*If you are properly hydrated, urine should be clear to pale yellow or straw colored. You should urinate every two to three hours during waking hours.

When you exercise, keep in mind these goals of hydration by SCAN (Sports and Cardiovascular and Wellness Nutrition):

  • Begin each exercise session well hydrated by drinking fluids during the day and within an hour before the session.
  • Replace sweat losses by drinking fluids regularly during exercise.
  • Rehydrate after exercise to replace weight loss as fluid during exercise.
  • Create and follow a personalized fluid replacement plan to prevent the consequences of excessive dehydration, which is defined as greater than two percent body weight loss. A personalized fluid plan will help you avoid early fatigue, cardiovascular stress, an increased risk of heat illness, and decreased performance.
  • Optimize ability to regulate body heat, especially in hot environments.
  • Improve ability to recover quickly from training and competition.

Other guidelines and tips for fluid intake during exercise include:

  • Water is fine for exercise lasting less than an hour.
  • Sports drinks are for moderate to high intensity lasting longer than 60 minutes, especially when carbohydrates and electrolytes are part of the nutrition plan.
  • Drink two cups of fluid during two hours before exercising.
  • Drink one to two cups within 15 minutes of activity.
  • Drink one half to one cup every 15 to 20 minutes during exercise.
  • Drink three cups for each pound of body weight lost.
  • Find a sports dietitian who can help you design a personalized hydration plan that considers thirst, urine color, sweat rate, and body weight changes under varying conditions of exercise.


Tsunami Certified Trainer, Cross Fit Level-1, Endurance, and Mobility
Sports Dietitian, Fitness Trainer, Ironman Triathlete

Deb is one of only about 700 Board Certified Specialists in Sports Dietetics in the United States. She enjoys helping athletes achieve optimal health and performance through food choices, body weight and composition. She is available for individual or group nutrition consults, as well as speaking engagements on a variety of nutrition topics for teams, clubs, or groups.