Micronutrient status, immune response and infectious disease in elderly of less developed countries.

Abstract

The world's population, especially in less developed countries, is expected to continue expanding. This growth is occurring together with a demographic transition due to increase in lifespan, and decrease in mortality and fertility. As a result, the number of people aged above 60 years in less developed countries is expected to increase from a current 8% to 20% in 2050, with the group above 80 years growing almost five fold1. When using country median age as an indicator of ageing, the 2006 Revision of the U.N. World Population Prospects shows that the overall world population will age (Figure 1) and that this shift will occur mainly in developing countries. But, even though lifespan has increased, quality of life has not improved for this age group2, leading to unhealthy ageing and increased morbidity. As it has been eloquently expressed on the 1995 State of World Health, “For most of the people in the world today every step in life, from infancy to old age, is taken under the twin shadows of poverty and inequity, and under the double burden of suffering and disease. For many, the prospect of a longer life may seem more like a punishment than a prize.” A primordial objective is not only to increase lifespan but to achieve successful ageing, which is defined as minimizing the time between the onset of illness and death3. Figure 1 Demographic transition towards and older population (United Nations, Population Division, 1999). Elderly in the less developed world play an important role in society and in their country's economy4. However, they are vulnerable to malnutrition and suffer from infectious diseases. Additionally, in the past years many elderly from less developed countries have experienced an increase in chronic diseases as a consequence of the double burden of malnutrition5,6. The increase of infectious and non-communicable disease within this expanding population has translated into poor quality of life and an increased burden on the healthcare systems of their countries. Subclinical levels of micronutrients have been associated with impaired immune function in people above the age of 607, and it has been found that micronutrient supplementation and improved nutrition can enhance immune function8,9. It is important, however, that more information is obtained on regional micronutrient status and the benefits a nutrition intervention might have. Such studies on elderly populations in the developing world are limited. Often data obtained from developed countries is applied to less developed countries, or has been extrapolated from younger age groups within the same country. Many aspects of populations in developed countries are not applicable to groups in less developed countries. Also, changes in health, physiology, and immune function during ageing make younger groups an inappropriate model for an older group. In this review we will describe age-associated changes in immune response, summarize the impact of micronutrients on immune status in the elderly, assess the current micronutrient status of the elderly in less developed countries and its relation to their immune response, and review current interventions to determine what they teach us for improving the health outcomes of this growing population, as well as the obstacles we need to overcome.