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a Departments of Internal Medicine, University of New Mexico School of Medicine, Albuquerque
b Departments of Family and Community Medicine, University of New Mexico School of Medicine, Albuquerque
c Departments of Pathology, University of New Mexico School of Medicine, Albuquerque
d Departments of Clinical Nutrition Program, University of New Mexico School of Medicine, Albuquerque
Robert D. Lindeman, Clinical Nutrition Program, Room 215, Surge Building, University of New Mexico Health Sciences Center, 2701 Frontier Place, N.E., Albuquerque, NM 87131-5666 E-mail: rlindeman{at}salud.unm.edu.
John E. Morley, MB, BCh
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Abstract |
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Methods. Equal numbers of Hispanic and non-Hispanic white men and women were selected randomly from the Health Care Financing Administration (Medicare) rolls and recruited for a home interview followed by a 4-hour interview/examination in a senior health clinic. Questionnaires and examinations were used to determine usual daily self-reported intake of fluids, lying and standing blood pressures, history of falls over the past year, and the presence of chronic constipation and chronic fatigue or tiredness. Serum samples were obtained for determination of sodium, urea nitrogen (SUN) and creatinine concentrations, and calculation of SUN/creatinine ratios.
Results. Interviews/examinations were conducted on 883 volunteers (mean age of 74.1 years). Most participants (71%) estimated that their usual fluid intake was equal to or exceeded six glasses per day. Evidence of hypernatremia (serum sodium concentration > 146 mEq/l) was not observed in the 227 individuals ingesting less than this. Hyponatremia also was rare in this population. Fluid intake showed no significant associations with lying and standing blood pressures, a history of falling, or the frequency of chronic constipation or fatigue/tiredness.
Conclusion. Until we have more evidence-based documentation that fluid intake of eight glasses (2 liters) per day improves some aspect of an elderly person's health, encouraging a fluid intake above a level that is comfortable for the individual seems to serve little useful purpose.
THE second edition of Dietary Guidelines for Americans was published in 1990 as a joint effort of the US Department of Agriculture and the US Department of Health and Human Services. Based on these dietary guidelines, a food guide pyramid was developed for educational purposes and has been publicized widely by the lay press. Russell and coworkers (1) recently proposed a modified food guide pyramid for people over 70 years of age; the guide recognizes that with advancing age, energy needs decrease, and therefore there should be a proportionate decrease in food intake. At the bottom of the pyramid, Russell and coworkers suggested that fluid or water intake equal to or greater than eight servings (glasses) or 2 quarts or liters per day was important to prevent dehydration in elderly persons, because they were less able to conserve salt (2) and water (3) and, most importantly, because they lost their normal thirst response (4).
We were unable to find good evidence that it was prudent for elderly, community-living persons to drink, as suggested, 2 quarts or liters of fluid (water) per day. In fact, one might speculate that there may be reasons to limit water intake, at least in some individuals. Elderly persons are less able to excrete a water load than younger persons and therefore might be more prone to develop a dilutional hyponatremia (water intoxication) with excessive water (5). Patients with congestive heart failure, hypoproteinemia, and liver or renal disease would be at increased risk.
The New Mexico Elder Health Survey (NMEHS) was a study of health and health-related issues in a sample of older (65 years of age and older) Hispanic and non-Hispanic white men and women selected randomly from the Health Care Financing Authority (HCFA) Medicare rolls of Bernalillo County (Albuquerque), New Mexico (6)(7). One of the objectives of the study was to perform a nutritional assessment that included a question about daily fluid intake. Because we also performed serum determinations of sodium, urea nitrogen, and creatinine, obtained lying and standing blood pressures, and asked questions about falls over the past year and about such symptomatology as chronic constipation and excessive fatigue or tiredness, we were able to compare participants with different levels of self-reported fluid intake to determine if there were any differences that suggested a benefit or adverse effect from this recommended high fluid intake.
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Questionnaires and Examinations
The nutritional assessment included the question, "How many glasses of liquids (including water, juice, coffee, tea, milk, wine, beer) do you drink per day?". Possible answers were (a) less than three glasses per day; (b) three to five glasses per day; or (c) six or more glasses per day. As part of a nurse practitioner's interview, other questions asked were whether the participants had (a) chronic constipation, (b) excessive tiredness or fatigue, or (c) a fall over the past year. Blood pressure and pulse were obtained with the participant lying comfortably on the examination table for at least 5 minutes. A subsequent blood pressure/pulse reading was obtained after the participant stood for 3 minutes. The blood pressure was obtained with a DYNAMAP Adult/Pediatric Vital Sign monitor (Critikon, Inc, Tampa, FL). A drop in systolic pressure on standing of 20 mm Hg and/or a drop in diastolic pressure of 10 mm Hg was considered consistent with orthostatic hypotension (8).
Laboratory Examinations
Serum determinations of sodium, urea nitrogen (SUN) and creatinine were obtained using standard autoanalyzer technology. A SUN/creatinine ratio was calculated. The range of normal values for healthy young adults as determined by the commercial College of American Pathologists certified laboratory (Reference Laboratory, Inc, Albuquerque, NM) was 138–146 mEq/dl for serum sodium concentrations, 9–21 mg/dl for serum urea nitrogen concentrations, and 0.4–1.4 mg/dl for serum creatinine concentrations. No range of normal values for SUN/creatinine ratio was provided, but a ratio 
20:1 was considered consistent with dehydration.
Statistical Analysis
Descriptive statistics included mean ± standard errors of the means (SEM) and frequency rates (%). In making comparisons between group frequency rates, the chi-square test was used. In making comparisons between groups on continuous measures, and where normality of the measure held, Student's t test was used. A logarithmic transformation of skewed variables, followed by a t test, was used when approximate normality could be obtained. Logistic regression models were developed for the primary outcomes (e.g., drop in systolic and diastolic pressure with standing, a history of falling over the past year, constipation and fatigue/tiredness), adjusting for gender, ethnicity, and age; for constipation, further adjustments for fiber intake and exercise were made. All analyses were made using SAS (9).
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, suggesting that this group was less well hydrated; however, this increase did not appear to be of any clinical importance. Using a logistic regression model fitting the SUN/creatinine ratio, with fluid intake per day as the predictor and age, ethnicity, and gender as covariates, the inverse association between the SUN/creatinine ratio and level of fluid intake then failed to reach levels of statistical significance 
Although the SUN/creatinine ratio tended to be slightly higher in the summer months (July and August) than in the other 10 months (mean ± SEM, 15.2 ± 0.32 vs 14.8 ± 0.16), this difference also was not significant 
. These data were reanalyzed looking just at the participants with serum creatinine concentrations 1.5 mg/dl or lower, so that those individuals with high serum creatinine concentrations would not skew the results. This eliminated 51 participants, equally distributed in the three groups, and made no difference in the results.
The individuals with serum sodium concentrations greater than 146 mEq/l and less than 132 mEq/l were determined to have hypernatremia or hyponatremia, respectively. Their records were examined to determine if causes could be identified for their sodium imbalances.
Two participants who had serum sodium concentrations greater than 146 mEq/l (147 and 150) were in the group with the highest reported fluid intake. Both participants were taking nonsteroidal anti-inflammatory drugs that could conceivably have inhibited prostaglandin release, because prostaglandins are mediators of vasopressin release. There were no other apparent reasons for the hypernatremia.
Four participants had serum sodium concentrations less than 132 mEq/l. Three were in the group with the highest fluid intake. Two participants with serum sodium concentrations of 131 mEq/l were 75 years old and on diuretics; one participant took a thiazide diuretic for hypertension, and the other, a carbonic anhydrase inhibitor for glaucoma. The third participant, with a serum sodium concentration of 127 mEq/l, was 73 years old with a history of cerebrovascular accident on anticoagulants. The participant with the lowest serum sodium of 126 mEq/l was from the group with an intermediate fluid intake and was 77 years old with cancer of the lung (cell type unknown), chronic obstructive pulmonary disease, resolving pneumonia, hypertensive heart disease with congestive failure, and diabetes mellitus with renal insufficiency, all of which could have explained the hyponatremia.
The changes in systolic and diastolic blood pressures incurred by assuming a supine to upright (standing) position were compared with variations in fluid intake. The logistic regression models fitted for the decreases in systolic and diastolic pressures with standing compared with fluid intake per day (adjusted for age, ethnicity, and gender as covariates) were not significant for either systolic (p = .81) or diastolic (p = .28) pressures. The prevalence of postural hypotension, defined as a decrease in systolic pressure 20 mm, or diastolic pressure 10 mm on assuming a standing position, was 6.5% and 6.6% of all participants, respectively. The presence of postural hypotension, based on these definitions, was marginally inversely associated with fluid intake after adjusting for age, ethnicity, and gender (odds ratio [OR] 0.40, 95% confidence interval [CI] 0.16–1.08, p = .06 for systolic pressure; OR 0.55, 95% CI 0.21–1.58, p = .12 for diastolic pressure). Similarly, symptoms (light headedness) on standing also were marginally inversely related to fluid intake (OR 0.62, 95% CI 0.35–1.13, p = .12). Similar analyses that relate falls over the last year to fluid intake failed to show any significant association or even trends.
The prevalences of chronic constipation and chronic fatigue/tiredness were determined in each of the three categories of water intake as shown in Table 1 . By chi-square analysis, there was a trend toward a higher frequency of chronic constipation associated with a low intake of fluid (p = .073), which almost reached levels of statistical significance. However, age, ethnicity, and gender each were found to be significantly associated with the frequency of chronic constipation. Constipation increased with age (5-year intervals) (OR 1.067, 95% CI 1.031–1.104, p < .001), was more frequent in Hispanics than non-Hispanic whites (OR 1.803, 95% CI 1.157–2.83, p = .010), and was more frequent in women than men (OR 1.582, 95% CI 1.019–2.473, p = .042). Using a logistic regression model adjusting for age, ethnicity, and gender, there was a much less impressive inverse association between fluid intake and presence of constipation (OR 0.847, 95% CI 0.530–1.380, p = .496). Elderly persons also exercise less frequently and ingest less fiber; women ingest less fiber than men. Neither dietary fiber nor exercise, when added into the logistic regression model also adjusting for differences in age, ethnicity, and gender, affected the association between constipation and fluid intake. There were no differences in the frequencies of excessive tiredness/fatigue between the three groups ingesting different quantities of fluids.
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70 years of age) should be encouraged to drink 2 quarts of water per day to avoid dehydration, because elderly individuals often lack the normal thirst mechanism (1). Elderly persons undoubtedly are more predisposed to the development of hypernatremic dehydration than younger persons. Snyder and associates (9) reported that more than 1% of their hospital admissions were patients over 60 years of age who developed hypernatremia (serum sodium > 148 mEq/l). Surgery, febrile illness, infirmity, and diabetes mellitus accounted for two-thirds of their cases. Half developed hypernatremia while in the hospital. Although this and other published articles describe the prevalence of hypernatremic dehydration in elderly patients admitted to acute care hospitals and in chronic care facilities (nursing homes), there is a lack of information about the prevalence of dehydration in community surveys, the population targeted by the modified food guide pyramid (1). In one study of 174 noninstitutionalized urban blacks aged 70–96 years (10), a high blood urea nitrogen (BUN) was reported in 23%, a high serum creatinine in 19%, and a high BUN/creatinine ratio (18) in 10% of the participants. One could not distinguish between who had high values caused by dehydration and who had renal insufficiency from other causes; however, a high BUN/creatinine ratio is more often a measure of dehydration, although poor perfusion caused by congestive heart failure could also explain a high value. The high values were associated with poor function on a variety of physical and cognitive function tests: the quality of life scale, falls, and measures of gait and balance. Only two individuals had a serum sodium >146 mEq/l (both 147 mEq/l); thus, hypernatremic dehydration, as in our population, was not a problem. Alterations in thirst perception were compared by Phillips and colleagues (4) in healthy young and elderly persons. After 24 hours of water deprivation, all subjects were given free access to water. Elderly subjects showed less thirst and drank less water, even though they lost more fluid and ended with higher serum sodium concentrations and osmolalities during the period of water deprivation. This absence of thirst is even more pronounced in individuals with cerebral disease (e.g., cerebrovascular accidents) (12). This loss of thirst unquestionably accounts for the increased tendency for elderly persons to become dehydrated, especially during periods of stress and illness (e.g., infections). We, however, found no evidence that fluid intake of less than six glasses per day was associated with hypernatremic dehydration, recognizing that this population was largely independent and healthy. One additional hypothesis that has not been tested is that elderly persons who chronically ingest large amounts of fluid may have a "washout" of the osmotic gradient in the renal medulla. This would leave them with a relative inability to concentrate their urine and thereby conserve fluids during a period of acute stress and dehydration, which again provides a reason why a high fluid intake might not be desirable.
On the other hand, surveys of elderly persons in both acute and chronic care facilities show a high prevalence of hyponatremia (13)(14)(15). In one study, 23% of chronically ill nursing home residents were hyponatremic (sodium concentrations < 132 mEq/l) (13). In most individuals, the low serum sodium was not readily explainable except by the presence of debilitating disease and old age. The earliest manifestations of hyponatremia are related to changes in cerebral function (e.g., lethargy, confusion) caused by shifting of water intracerebrally (brain swelling) along an osmotic gradient. It is generally difficult in these populations to determine if the hyponatremia is responsible for any symptomatology.
In another nursing home study (14), over half of the residents had been hyponatremic (sodium concentrations 
135 mEq/l) on at least one occasion over the previous year. The most common etiology was an increased fluid intake, either orally or intravenously, occurring in 78% of cases. The hyponatremic residents excreted much less of a water load over a 5-hour period and failed to dilute their urine as much as nonhyponatremic residents. In still another nursing home study (15), the use of thiazide diuretics was found as a common possible etiology in hyponatremic residents.
Miller and colleagues (16) subsequently reported a prevalence of hyponatremia of 11.4% (serum sodium < 135 mEq/l) in an ambulatory geriatric clinic population. Of 46 patients with hyponatremia, 27 (59%) had an etiology linked to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) (e.g., neoplasm, pulmonary, or central nervous system disease or medications), whereas the remainder had an etiology (e.g., cardiac, renal, or hepatic disease, diuretic use, or volume depletion) not generally related to this entity. In the former group, there were seven individuals (1.7% of the total clinic sample) for whom there was no explainable etiology (idiopathic). The evidence for and possible reasons why elderly subjects are more prone to develop hyponatremia of the SIADH variety is discussed elsewhere (17)(18).
This raises the interesting possibility that encouraging fluid intake too vigorously in elderly persons might lead to hyponatremia (water intoxication) in some. We observed hyponatremia (serum sodium concentration < 132 mEq/l) in only four of the 796 (0.5%) participants who agreed to have blood samples drawn and answered the question about their fluid intake. All four had a potential explanation for their hyponatremia. We used a lower serum sodium concentration to define hyponatremia than the one used by Miller and colleagues (15) in their ambulatory population, although it is doubtful that symptoms would result from a serum sodium concentration of 132 mEq/l or greater. Nevertheless, we would have seen only 24 participants with less than 135 mEq/l (3.0%), which is still well below the prevalence reported by Miller and colleagues (15). This difference is not surprising given that a clinic population represents a sicker group than a randomly selected population of elderly persons.
One of the recommendations for management of chronic constipation is to drink lots of water and get lots of exercise. Again, the evidence-based documentation that a high fluid intake is effective in avoiding chronic constipation is hard to find. The chi-square test comparing fluid intake with the presence of self-reported chronic constipation shows evidence of a moderate inverse association (p = .073). This analysis has several limitations in its ability to answer the question posed as to whether a high fluid intake decreases the chances for developing chronic constipation. First, because of the cross-sectional design of the study, we can only look at associations and not distinguish between cause and effect. Second, we have not restricted our analysis to independently living, relatively healthy, and active individuals aged 70 years and greater as targeted for the Russell pyramid (1); instead we have used a randomly selected population of individuals aged 65 years and older, including the frail elderly, homebound, and those in nursing homes. Third, both fluid intake and chronic constipation are self-reported, with only three categories of fluid intake. Finally, no definitions or criteria for chronic constipation were provided to the participants to give uniformity of reporting. Therefore, we would expect some degree of nondifferential misclassification error in the reported responses, which tends to bias the analysis toward the null hypothesis. Furthermore, participants with chronic constipation may be more aware of their fluid intake than are those without constipation, giving us a biased response (i.e., reporting a higher intake than actual consumption). This also might increase the probability of finding no association when a true association is present.
Another limitation of this analysis is the possibility of confounding (e.g., the observed association [or lack of association] may be due to the presence of an unidentified factor that is associated both with the exposure [fluid intake] and the outcome [constipation]). Age, sex, and ethnicity all were associated with the levels of fluid intake and therefore were examined as potential confounders of the fluid–constipation relationship. Other potential confounders that were examined were fiber intake and exercise, because people who drink more water also might be eating more fiber and getting more exercise. Using logistic regression models, adjusting for these potential confounders, most of the moderate inverse association between fluid intake and the presence of chronic constipation was lost.
Perhaps the most compelling evidence for elderly persons to maintain a high fluid intake was recently presented by Michaud and coworkers (19). An analysis of the risk for bladder cancer among 48,000 male participants in the prospective Health Professionals Follow-up study, followed over a 10-year period, shows a strong inverse association between the consumption of fluids (most notably water) and the incidence of bladder cancer. The authors review the existing literature relating risk of bladder cancer to known carcinogens, for example, smoking, and the source and quantity of fluids ingested (coffee, alcohol, and possible contaminants in water supplies). An associated editorial (20) describes the "urogenous contact hypothesis" relating how the duration and concentration of putative carcinogenic agents in contact with urinary tract epithelium could directly influence the potential for development of bladder cancer (i.e., a higher urine flow should decrease contact and risk). Another consideration is that a higher fluid intake might decrease the frequency of kidney stone formation, but generally "stone formers" would have been identified at a younger age and been encouraged to drink more fluids.
On the downside, increased fluid intake leads to increased urine volume and more opportunities for urinary incontinence, which can be a major inconvenience for elderly persons and their caregivers. Also, encouraging fluid intake after dinner can result in frequent awakening at night and resultant loss of sleep.
Because we only can identify participants who have a fluid consumption of six or more glasses per day compared with those ingesting less, we are not able to examine the potential beneficial versus adverse associations of the eight glasses per day as recommended in the Russell pyramid. We suggest that until there is more evidence that encouraging a fluid intake above a level that is comfortable for the elderly individual serves a useful purpose, this approach should not be pursued. Certainly there are other preventive measures about which patients can be counselled that have more potential for improving quality of life.
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Acknowledgments |
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Received January 24, 2000
Accepted March 9, 2000
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This article has been cited by other articles:
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  J. E. Morley and J. H. Flaherty Editorial It's Never Too Late: Health Promotion and Illness Prevention in Older Persons J. Gerontol. A Biol. Sci. Med. Sci., June 1, 2002; 57(6): M338 - 342. [Full Text]
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D. R. Thomas, W. Ashmen, J. E. Morley, and W. J. Evans Nutritional Management in Long-Term Care: Development of a Clinical Guideline J. Gerontol. A Biol. Sci. Med. Sci., December 1, 2000; 55(12): 725M - 734. [Abstract] [Full Text]
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