As temperatures and humidity levels rise in the summer months, hydration and heat acclimatization become increasingly vital in maintaining physical and mental health and maximizing performance.   

Research from the Exercise Physiology Laboratory, led by Professor Mindy Millard-Stafford, director, and Adjunct Professor Mike Sawka in the School of Biological Sciences, aims to help athletes and occupational workers better understand and prevent sweat loss and dehydration through the development of predictive tools. 

Heat Acclimation Takes Time  

According to Millard-Stafford, it can take between five and seven days of active exposure in hot conditions to properly acclimate the body to extreme temperatures. During this period, taking frequent breaks, along with proper hydration, is necessary while the body attempts to thermoregulate through the evaporation of perspiration. She also advises easing into a full workload or exercise routine, if possible, and seeking shade with intermittent breaks when working outdoors for long periods.   

Sawka, retired senior scientist for environmental medicine, stressed that even those familiar with summer conditions can be susceptible to the symptoms of overheating following months of cooler temperatures or indoor activity. A predictive tool developed by collaborating with the University of Canberra, Australia, and recently published in the Journal of Comprehensive Physiology illustrates the benefits of heat acclimation based on environmental factors like temperature, humidity, duration of exposure, and other factors to inform their training and recovery plans.  

"Just like you train for your activity, whether it's running or tennis or basketball, it's the same with adapting to environmental extremes. It's specific, and the tool allows you to input the unique conditions you will attempt to acclimate to," he said.    

Staggering start times can also effectively mitigate injury and heat-related incidents until an individual is properly acclimated to the climate.    

Staying Sharp 

Studies from the Exercise Physiology Laboratory have revealed a drop in performance and cognitive function when subjects lose 2% of their body mass during exposure to heat. Without proper planning and fluid replacement, thermoregulation can be hindered, cardiovascular strain increases, and an individual's energy levels and performance can diminish. As more body water is lost, more significant symptoms can occur.  

The amount of sweat lost during heat exposure is another key indicator of how much fluid an individual needs to avoid these symptoms. A sweat loss prediction calculator, recently published in the Journal of Applied Physiology and funded by Coca-Cola in collaboration with the University of Sydney and Canberra University, uses predicted output and other factors to help individuals plan hydration management strategies for exercise in hot conditions. Relying solely on thirst as a guide frequently leads to underhydration by nearly 50%; therefore, fluids should be consumed before, during, and after exposure to heat.   

Understanding sweat loss can also help individuals avoid the dangers of overhydration. "This is not a 'more-is-always-better' kind of approach. You can run into problems by drinking too much over extended periods while exercising," Millard-Stafford said. "Hyponatremia, or water intoxication, can be lethal. You want to follow the Goldilocks theory of ‘not too much and not too little’ to maintain fluid balance with the sweat loss calculator.”   

Elderly adults are at an increased risk of heat-related incidents, even if they aren't outside as much, due to differences in their body's ability to regulate temperature and potential adverse effects of medication such as diuretics. Older adults also have a diminished thirst sensation when dehydrated, so they tend to underdrink.   

More Than One Way to Hydrate 

Eighty percent of human hydration comes from consuming liquids, while the remaining 20% comes from food. Millard-Stafford recommends adding more fresh fruits and vegetables as a part of your diet over the summer.  

Drinking fluids remains the primary combatant against dehydration, but she and Sawka also recommend pre-planning meals that include sodium to better retain fluids and nutrients. Humans generally rehydrate at mealtime, with food stimulating thirst and fluid consumption,  helping cells maintain balance. Electrolytes in sports drinks can also help hydrate during and after sustained heat exposure.  

For many, simply choosing not to go outdoors in the heat is not an option. So, Millard-Stafford and Sawka continue to share best practices and strategies to avoid heat-related illness and dehydration while optimizing performance.