Warming weather may heighten the risk of hypohydration

Zachary J. Schlader, PhD, FACSM

In many parts of the northern hemisphere, as the calendar turns from winter to spring and then from spring to summer the public and people in many workplaces will be exposed to more intense and frequent days of high heat and humidity. Work or physical activity (such as exercise) in hot conditions can challenge health and safety, by increasing the risk of heat illness, and reduce sustainable work rate, which can decrease productivity and performance. The goal of the body’s temperature regulation system during work or exercise in the heat is to get rid of excess body heat to maintain internal body temperature within a normal and safe range. To accomplish this, the body has two primary methods to promote heat loss – increased skin blood flow and sweating. Increasing skin blood flow involves the cardiovascular system, while sweating involves the movement of body water onto the skin to lose heat when the sweat evaporates. Both processes require adequate body water for optimal functioning, and when body water is decreased the ability to regulate body temperature is worsened. Notably, when fluid intake is not sufficient to offset the loss of body water due to sweating, hypohydration (a loss of body water) can ensue. Hypohydration (which is often also termed dehydration) is common during work/exercise in the heat given the increased sweat loss and the observation that when people are allowed free access to fluids, they often under drink. Hypohydration should be minimized not only because of its negative impact on thermoregulation, but also its detrimental effects on the cardiovascular system, challenges to the kidneys, and the increased likelihood for cognitive and behavioral dysfunction, all of which can negatively impact health and safety, and reduce productivity and performance. 

The risk of hypohydration is likely heightened as the calendar transitions towards summer. 

This is because people are less likely to be acclimatized to the heat during this time of year. Heat acclimatization is defined as a series of adaptations that enhances the body’s ability to tolerate and function during work/exercise in the heat due to improvements in thermoregulation and fluid regulation. The importance of seasonal heat acclimatization is emphasized by observations that hospitalizations and deaths during heat waves are greater in the late spring or early summer compared to later in the summer. One of the important aspects of heat acclimatization is the expansion of body water and improvements in fluid intake that better enable the matching of drinking to fluid losses, which subsequently minimizes the risk of hypohydration. Thus, with the changing of the calendar and warming weather there is an increased risk of hypohydration. 

Tips for preventing hypohydration early in the ‘heat season’:

Ensure easy access to cool drinkable fluids. Water is generally fine, but if work in the heat is prolonged (>2 hours) consider fluids with electrolytes. Remember to drink early and often. Monitor urine volume and color to estimate hydration status – if the need to urinate is infrequent and the urine is dark, drink more. Seek shade or a cooler environment, when possible, to reduce the need to sweat. Remove unnecessary clothing if possible. If only non-drinkable water is available, consider spreading the water on the skin to promote heat loss and minimize the requirement for sweating.