Despite its high relevance in public health, prevalence of dehydration has been poorly investigated, especially in healthy community-dwelling elderly (not in assisted living or nursing home) (Stookey et al. 2005a).
Nevertheless, existing evidence is strongly suggestive of high rates of dehydration in the elderly within hospitals and other healthcare institutions (Begum and Johnson 2010; Himmelstein et al. 1983; Warren et al. 1994; Snyder et al. 1987; Bennett et al. 2004; Mentes et al. 2006a; O’Neill et al. 1990; Bourdel-Marchasson et al. 2004; Forsyth et al. 2008). In fact, dehydration is a frequent cause of hospitalisation of older adults and one of the ten most frequent diagnoses responsible for hospitalisation in the United States (Sheehy et al. 1999). Studies in nursing homes also reveal high rates of dehydration in this population. For instance, one study indicates that the prevalence of dehydration in older residents of continuing care facilities was as high as 88% when assessed by plasma osmolality (O’Neill et al. 1990). Another study is also suggestive of a high prevalence, by showing that 31% of nursing home residents encountered dehydration defined as high blood urea nitrogen to creatinine ratio, hospitalisation and administration of intravenous fluids for rehydration (Mentes 2006c). This is in line with studies indicating that between 50% to 92% of nursing home residents have inadequate fluid intakes (Mentes and Kulp 2003).
In contrast, data are more conflicting in the community-dwelling elderly (Stookey 2005b).
While some studies found no evidence of dehydration (Morgan et al. 2003; Bossingham et al. 2005), one found that the prevalence of hypertonicity, a measure of dehydration, may be as high as 60% (Stookey 2005b). It is likely that actual prevalence of dehydration among community-dwelling elderly adults varies depending on the indicator used to define hydration (Stookey et al. 2005a).
As daily water needs strongly depend on various factors like fluid losses and dietary composition, the estimation of water requirement is highly variable and quite complex. This is particularly true for the elderly for whom health conditions such as congestive heart failure and kidney diseases or medication use (diuretics or laxatives) highly influence fluid needs (Volkert et al. 2005).
Only a few countries have established national recommendations for fluid intakes (Popkin et al. 2010) and existing recommendations vary between countries (EFSA 2010; IoM 2004). For instance, the Institute of Medicine of the National Academies of Science in the United States defined in 2005 a recommendation for total fluid intake (water provided from beverages and foods) of 3.7L and 2.5L for the elderly men and women respectively (IoM 2004). In Europe, the European Food Safety Authority has recently set a reference value for total fluid intake (water provided from beverages and foods) of 2.5L for elderly men and 2L for elderly women (EFSA 2010).
Despite the general consensus that an appropriate level of fluid intake is essential for health, little work has been done to date to measure total fluid intake, especially in the older population (Popkin et al. 2010; Bellisle et al. 2010).
The few studies, including nationally-representative studies, addressing the measurement of fluid intake in the elderly (Volkert et al. 2005; Bellisle et al. 2010; Haveman-Nies et al. 1997; Raman et al. 2004; Zizza et al. 2009; Kant et al. 2009) reveal that total fluid intake steadily decreases with age within the elderly population and that this decrease is mainly driven by a decrease in water intake from beverages (including drinking water) (Volkert et al. 2005; Raman et al. 2004). Comparisons between observed fluid intakes and local or regional recommendations indicate that a substantial proportion of the elderly population may be at risk for insufficient fluid intake and thereby of dehydration, especially among seniors over age 85 (Volkert et al. 2005; Haveman-Nies et al. 1997; Zizza et al. 2009; INVS and CNAM 2006).
For example, a German study conducted in independently living elderly found that one-third of this population did not meet the German reference value for total fluid intake. This poor total fluid intake was reflected by a low level of fluid intake from beverages (Volkert et al. 2005). Similarly, an American study indicated that about two-thirds (63%) of the young elderly (65-74 y) and the vast majority (81%) of the oldest elderly (85+ y) have inadequate total fluid intake based on recommendations from the Institute of Medicine (IoM 2004) (Figure 4).
Although data on dehydration frequency in community-dwelling elderly are conflicting, comparison of their actual fluid intakes with current recommendations clearly indicates that the aging population, whether in healthcare institutions or in the community, is at risk of inadequate fluid intake, and therefore is exposed to dehydration.