Effects of an Active Lifestyle on Water Balance

Water is the most abundant chemical constituent of the human body, typically making up approximately two thirds of body mass, but body water content is maintained within relatively narrow limits by a number of regulatory mechanisms. Both a reduction (hypohydration) and increase (hyperhydration) in body water may, if sufficiently severe, lead to adverse health and performance consequences. Active lifestyles, warm climates, and high altitude, as well as some infectious illnesses, increase the likelihood of becoming hypohydrated due to an increase in water loss. Moderate reductions in body water result in changes in cardiovascular system function as well as altering cognitive function and mood. A significant number of elite athletes, recreational exercisers and those with active occupations begin their daily activities in a hypohydrated state and incur large sweat losses during periods of activity, and thus risk negative effects on physiological function. Sweat rate and fluid intake during physical exertion are highly variable between individuals suggesting that an individual hydration strategy may be necessary to avoid significant levels of hypohydration. Rehydration after the completion of physical activity may also be necessary to avoid starting further bouts of activity in a hypohydrated state. Undertaking physical activity in a hypohydrated state appears to increase an individual’s perceived exertion which may negatively influence exercise performance and self-selected exercise intensity, and may decrease the likelihood of further participation in physical activity. This is, therefore, an important consideration for public health as well as competitive sportspeople, be they elite or otherwise. Certain populations, such as the elderly, are more likely to become hypohydrated which may lead to other illnesses and contribute to morbidity and mortality