The latest article in the series "A New Look at the Old," features studies on the serious problems that can develop for senior citizens that become dehydrated, including higher risk of coronary heart disease. Age-related changes make older adults more vulnerable to shifts in water balance that can result in over-hydration or, more frequently, dehydration.

Author Janet Mentes, PhD, APRN, BC, found in a study of long-term care residents that 31 percent were dehydrated. 

She also reports in her article, "Oral Hydration in Older Adults," on another study that found 48 percent of older adults admitted to the hospital from Emergency Departments had laboratory values indicative of dehydration.
She writes that "greater awareness is needed in preventing, recognizing and treating dehydration."

With sufficient fluid consumption older people tend to have fewer falls, less constipation and laxative use, improved rehabilitation in orthopedic patients and a reduction in bladder cancer (among men). 

Drinking five or more 8-oz. glasses of water a day is also associated with lower rates of fatal coronary heart disease in middle-age and older adults, reports Mentes.

She warns that the body's thirst response becomes blunted with age. As a consequence, many of older patients may be dehydrated – a condition that leads to severe consequences if not identified and treated. 

Dehydration in the elderly is not just caused by inadequate fluid intake. Other causes include diarrhea, excessive sweating, blood loss, fluid accumulation and fever. Illnesses that entail excessive urination, such as diabetes and hypercalcemia, may also put people at risk for dehydration.

With aging, it becomes more difficult for the body to maintain fluid balance. There are several reasons, says Mentes.

The thirst response, which is the body’s primary mechanism of signaling the need for fluid, becomes blunted with age. This was apparent in a 2002 trial that compared men 51 to 60 years of age with those 20 to 28 years of age. During a strenuous 10-day hill-walking excursion, the older men had less thirst and became progressively dehydrated; younger participants had no dehydration. 

An earlier study found that in older men, the serum markers of dehydration (serum osmolality and sodium level) took longer to return to normal after an episode of dehydration than they did in younger men. 

Total body fluid

From puberty to 39 years of age, total body fluid is about 60% of body weight in men and 52% in women; after age 60, total body fluid decreases to about 52% of body weight in men and 46% in women. Women have a higher percentage of body fat and less muscle mass than men do and therefore less total body fluid.

In addition, muscle mass is lost with age, increasing the proportion of fat cells, which contain less water than muscle cells do, resulting in a decrease in intracellular fluid volume.

Decline in kidney function 

Creatinine clearance, an indicator of the kidney’s efficiency in filtering toxins from the blood, can decline with age. In one study, researchers found that in “normal” patients, the “mean decrease in (creatinine clearance) was 0.75 mL/min/year” after age 40. 

“Normal” patients were those who didn’t have renal or urinary tract disease or use diuretics or anti-hypertensives. (However, the authors also noted that “one-third of all subjects followed had no absolute decrease in renal function.”) This decline in function means that the kidneys are less able to concentrate urine, so water is lost that in a younger person wouldn’t be.

This newest article in the American Journal of Nursing New Look at the Old series provides current research about the hydration status of older adults across care settings and in the community, as well as a range of tools to improve your assessment skills, including a "Dehydration Risk Appraisal Checklist."

This study and all in the series are presented free online by the American Journal of Nursing and most are accompanied by videos.