This study fills a gap in the literature by defining the water intakes of a nationally representative sample of middle-old and oldest-old adults. Results from this study indicate that total water intakes appear to decrease with age. This decrease is observed even when considering body weight and caloric intake. Contrary to our results, two smaller area-specific studies found no differences in fluid intake between younger and older adults (21
). However, neither study included participants in the oldest-old age group. Comparable with our study, but using a representative sample of older German adults, Volkert and colleagues (3
) reported that total daily water intake and daily beverage intake decreased with age and found that those 85 years or older had the lowest water intakes. Using hydrogen-labeled water, Raman and colleagues (34
) found that water from ingested foods and beverages did not differ significantly among age groups until the eighth decade of life. In a smaller British study, researchers reported that average daily water intakes of community-living older adults (69–88 years) were lower than those found in younger populations (35
As expected from the total water intakes, the proportion of study participants meeting their AI was the lowest in the oldest-old group. AI is based on the intakes of healthy individuals who appear to be adequately hydrated; however, individuals can be adequately hydrated at lower or higher levels. However, having so few study participants meeting their AI warrants further investigation.
The credibility of the “8 × 8” (eight 8 ounce glasses daily) water recommendation has been questioned (36
). No single measure completely discriminates between dehydrated and nondehydrated individuals (5
). Lindeman and colleagues (20
) suggested that eight glasses of liquid a day may be inappropriate and actually may contribute to incontinence and/or water overload. More recently, Negoianu and Goldfarb (1
) questioned the validity of the commonly held belief that adults should drink eight glasses of water per day. Overall, there has been little research to measure the fluid intake of community-dwelling older adults, and fluid intake recommendations for all adults should be evidence based (19
). Thus, our aim was to provide a population-level assessment of water intake to assist in the development of evidence-based fluid intake recommendations for older adults.
There were interesting differences between the water contributions of meal and snack beverages. The water intake from beverages consumed as snacks decreased significantly as the age of the population increased. The role of snacking in a healthful diet has been questioned (31
). Our results suggest that the consumption of beverages during snack occasions may play an important role in maintaining fluid homeostasis.
There were also differences in the timing of beverage consumption; most beverages were consumed in the morning, whereas few were consumed at night. This finding, and that of De Castro, supports the claim that older adults may deliberately avoid drinking in the evening in order to avoid nighttime incontinence (6
Although there has been a clear societal trend toward soda consumption and away from milk consumption (37
), we found that milk beverages were the second leading source of water for the middle-old and oldest-old and that soft drinks were the second leading source of water for the young-old. Some have suggested that these differences may be a cohort effect rather than an effect of aging (21
). However, this may be an actual behavior change associated with aging. Jungjohann and colleagues (23
) found that elderly men drank significantly fewer soft drinks than the same men did when they were younger. Researchers examining total diet quality have shown that dietary behaviors become more health promoting as individuals age (38
Coffee and tea consumption were common in our study population. Many health professionals advise individuals to avoid coffee and teas because they contain caffeine and related methylxanthine compounds (39
). It is commonly believed that these beverages may trigger dehydration because of their diuretic effects (3
). However, Maughan and Griffin (39
) found little evidence supporting this hypothesis. The authors noted that little is known about the influence of age and gender on the diuretic effect of caffeine. However, recommendations for older adults to decrease caffeine consumption may be appropriate considering its other stimulant effects and the potential for drug interactions.
One drawback to this analysis is the use of only one 24-hour dietary recall interview. Water intake may vary from day to day. In addition, underreporting issues can be an issue with self-reported data such as a 24-hour dietary recall interview. In a study that examined underreporting issues, the results obtained from 30-year-olds were significantly different than those obtained from older age groups (40-, 50-, and 60-year-olds), but differences were not found when comparisons were made between the older three age groups (40
). All our participants were noninstitutionalized; however, there may be the possibility of cognitive impairment in these participants, and this would affect their ability to recall their diet. Another drawback is that we were unable to control for environmental variables (geographical location, seasonality) that could influence water intakes. The AI is for individuals living in temperate climates; thus, we may have misclassified individuals residing in warm climates. With our analysis, we are unable to determine the clinical significance of the observed decrease in water intake. A review of literature in the dietary reference intakes report suggests that increased total water intake may be effective therapy to prevent recurrent kidney stones, gallstones, distal colon tumors, and bladder cancer (41
An advantage of our study is that we used a nationally representative sample that allows us to generalize to the U.S. population. Another advantage is that we were able to examine adults 85 year or older. Finally, a 24-hour dietary recall allowed us to describe behaviors affecting beverage intake such as timing and beverage selection, which are important considerations when trying to implement behavior change.
Our results suggest that water intakes, particularly the contribution from beverages, appear to decline with age. Future research needs to investigate the clinical outcomes associated with declining water intakes of community-dwelling older adults. Identifying the associations between water intakes and clinical outcomes will also assist in evaluating and determining evidence-based water intake recommendations for older adults.