A new study confirms that older men may lack the bodily cues that help younger men remain hydrated.

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Smart thermostats have nothing on our hypothalamus. This is the gland that helps us maintain a healthy body temperature.

When we get too hot, the hypothalamus causes our skin to produce sweat that cools us down as it evaporates. We then become thirsty, and we should drink to replace the water that we lost through sweating.

However, if we sweat too much or do not drink water to replenish our fluids, we can become dehydrated.

Without enough water in the body, we lose the ability to cool ourselves with sweat, and the body can overheat. This increases our chance of experiencing heatstroke and other heat-related damage to our bodies.

As we age, the efficiency of our temperature regulation system declines. Although most research into the effects of dehydration focuses on young adults, a new study in The Journal of Physiology examines its role in the health of older adults.

Older adults may not feel as thirsty as young people and should take care to hydrate when they work or exercise and when the weather is hot.

Researchers from the Human and Environmental Physiology Research Unit at the University of Ottawa in Canada explored the paradoxical risk associated with dehydration later in life.

On the one hand, during exercise, dehydration in older adults does not lead as readily to an increase in body temperature through a reduction in heat loss as it does in younger people.

Although this may seem to be a good thing, the lack of sweat and thirst means that the person loses important cues that suggest that it is time to rehydrate.

Without drinking enough water, dehydration in older adults may persist and quietly increase to dangerous levels.

Scientists have suggested that the reason that older adults feel less thirsty is due to a reduced ability to detect and respond to the level of salt in their blood.

When the balance between water and salt in the blood tips toward salinity, the body of a younger adult responds with feelings of thirst.

The researchers wondered if the same reduced ability to track blood salinity, or “osmolality,” that reduces sensations of thirst may also be the driver behind the less extreme response to dehydration in older adults.

Ten younger men (18–30 years old) and 10 older men (54–67 years old) participated in exercise heat stress tests. The researchers asked them to abstain from consuming alcohol and engaging in strenuous exercise for 24 hours before each session. They also asked them to drink 500 milliliters of water the night before the experiments.

After screening, the men took part in two exercise sessions placed a week apart. At the start of each exercise session, the participants received an intravenous saline solution to increase blood osmolality before entering a heated, whole-body direct-air calorimeter for 1 hour of stationary cycling.

The calorimeter measured the participants’ whole-body evaporative and dry heat loss, and other measurements tracked a range of body indicators of temperature and rate of heat loss.

Analysis of these data revealed a substantive difference in the regulation of body temperature between the younger and older men.

The researchers found that for older men, an increase in blood salinity did not trigger the body’s responses to dehydration as it did in the younger men.

Further research will be necessary to help scientists gain a full understanding of heat regulation in older adults.

As first study author Robert Meade says, “While our research design allowed us to test the independent effect of osmolality on heat loss, the effect of reduced blood volume (termed hypovolemia) on sweating in older adults is currently unknown.”

Because the study explored the effects of blood osmolality in physically active participants without any known chronic conditions, it is unclear whether or not the same finding would apply to older adults with common age-related conditions such as type 2 diabetes.

However, Meade concludes:

“Given that common age-related chronic health conditions such as type 2 diabetes are associated with less efficient regulation of body temperature and hydration status, future research should be conducted to see whether our findings translate to or are exaggerated in those populations.”