Unlike antidiuretic hormone secretion, however, the increase in thirst following dehydration
decreases with aging. During dehydration older individuals report less thirst despite having
similar increases in plasma tonicity as younger individuals. This lower perceived level of
thirst is associated with reduced level of fluid ingestion. As mentioned earlier, most people
will not drink enough water to replace their original fluid deficit, and this problem is
exacerbated with age. Thus, thirst cannot be used as a reliable indicator of the fluid
requirements of older individuals. This is probably an expected conclusion since a variety of
sensory functions (e.g. hearing, vision, smell and touch) are also generally reduced with
aging.
ACSM CURRENT COMMENT
In summary, the important body mechanisms used to regulate body water content are
compromised with aging. The capacity to respond to dehydration and retain water is limited
while thirst sensations, and thus the drive to replace fluid, is also reduced with aging. In
addition, other factors associated with aging can exacerbate this problem. For example,
hormonal changes associated with menopause, the occurrence of chronic medical
conditions (e.g. hypertension), the use of certain medications or behavior adjustments to
solve urinary incontinence problems, can increase the risk of water imbalance in older
individuals. Older individuals and their families must be aware of the age-related changes in
hydrational needs in an effort to reduce the risk or prevent disturbances in fluid balance.