Hydration, thirst and fluid balance in resting and exercising individuals

Adequate fluid consumption is central to human survival. Previous literature suggests that there some misconceptions regarding hydration and fluid balance in some populations. Available data also show that the role of thirst sensations in maintaining fluid balance in different settings is also equivocal. Therefore, this thesis aimed to examine the perception of hydration, thirst and fluid intake in freeliving populations, to examine the feasibility of thirst as a marker of hydration status and to investigate the effect of thirst related sensations on fluid balance in resting and exercising individuals under different ambient temperatures. The findings in this thesis (Chapter 3) show that individuals who work within the fitness industry demonstrated substantial knowledge about drinking practices, hydration status and health consequences of water consumption, but lack understanding on the type of beverages that adequately hydrate the body. Further, thirst perception and mood states did not affect (P>0.05) the fluid intake in free living individuals (Chapter 4) and resting individuals under cool and warm exposure (Chapter 6), but some other factors such as subjective feelings of mouth dryness and the extent of hydration status might influence the fluid intake behaviour in these populations. In addition, following ingestion of flavoured carbohydrate drinks, thirst sensations was rated lower over time (P<0.05) during exercise in the cool, but was higher over time in the warm temperature (Chapter 7). Moreover, subjective feelings related to dehydration such as mouth dryness, thirst perception, desire to drink (water pleasantness) and hunger rating could be used as index of hydration status to signify at least a 1% body mass loss due to food and fluid restriction in resting individuals (Chapter 5). In conclusion, the findings in this thesis provide some new insight with respect to hydration, thirst and fluid balance in different populations under different settings. Nevertheless, some inconclusive findings regarding the role of thirst related sensations in fluid balance require further investigations.