The role of nutrition in immunity in the aged.

Abstract

The proportion of aged individuals has rapidly increased in the second half of the twentieth century in both Westem and developing countries. One of the major consequences of this growing elderly population is the significant increase in health care expenses. For example, although persons over the age of 60 years represent only 17% of the French population, nearly half of the nation’s health care resources are dedicated to them, due to their increased susceptibility to infection and other diseases. This increase in the population of elderly people will continue for at least thirty more years (until 2025); health care expenses will also rise accordingly. Consequently, the health care systems of many countries are undergoing drastic revisions. Growing scientific and popular interest in aging process has led to increased finding for aging research, which focuses not only on age-related pathologies but also on research on the normal aging process. The aging process is influenced by several factors, of which genetic background, exposure to environmental factors such as nutritional habits, and exposure to antigens are the most important. Nutrition, in particular, has been recognized to influence age-related diseases (Lesourd 1990a, Feldman 1993), such as the relationship between lipid consumption and cardiovascular disease (Wei 1992) and the prevention of age-related bone fractures (Lesourd et al. 1992a). Both of these examples figure prominently in the increased spending on health care. Furthermore, the increased mortality associated with infection during periods of famine provides additional evidence of the influence of nutrition and nutritional status on defense mechanisms (Chandra 1992a). Despite increased health care expenditures, infection remains the fourth leading cause of death in the elderly (Chandra 1989). In particular, the elderly are more susceptible to viral infection than their younger counterparts, with lung infections in hospitalized elderly patients representing the most monoclonal prevalent infection. Furthermore, influenza is one of the main causes of mortality in elderly people (Sprenger et al. 1991, McBean et al. 1993), especially those who are undernourished and, therefore, unable to increase their antibody levels after influenza vaccination (Chandra et al. 1984a, Lesourd 1990b). In addition, undernutrition has been identified as a major contributing factor to morbidity and mortality in hospitalized aged patients (Sullivan et al. 1990, Sullivan and Walls 1995a), in recovering aged patients after hospital exit (Sullivan and Walls 1995b), as well as in free-living, apparently healthy elderly (Klonoff-Cohen et al. 1992, Corti et al. 1994). Undernutrition increases the risk of infection in the elderly, which is directly proportional to the degree of undernutrition (Sullivan and Walls 1995a). With recent developments in understanding the finction and regulation of the immune system in the last thirty years, the relationship between nutrition and immunology has become better understood (Scrimshaw et al. 1988, Chandra 1988, Bendich 1990, Chandra 1992qFeldman 1993, Chandra and Kumari 1994, Meydani et al. 1995). Although both nutrition and immunology play an important role in the aging process, it has only been recently that the influence of nutrition on the aging immune system has been investigated (Moulias et al. 1985a, Meydani et al. 1986, Chandra 1989, Lesourd 1990a, Lesourd 1990b, Chandra 1992a). The purpose of this review is to focus on the interrelation of immunity and nutrition in old age, concentrating on five key questions: (1) What are the main features of the aging immune response-is it characterized by a global decrease in immune response (Makinodan and Kay 1980) or a dysregulation of the immune system (Weksler 1995)? (2) What is the importance of undernutrition in aged individuals? (3) What is the importance of age-related nutritional deficiency on the immune response of aged individuals (Lesourd 1990a, Lesourd 1990b)? and (4) Are nutritional interventions usefil in preventing or modifying age-related changes in the immune system? And if so, ( 5 ) Are they of any clinical relevance? We focus essentially on “healthy” elderly, a very rapidly growing population in Western countries, for whom good health maintenance not only permits a high quality of life after retirement (a growing concern of people aged 60-80 years) but