The discussion of nutrient requirements and recommended dietary intakes of nutrients in older persons has proceeded on both the theoretical and empirical level. Since the peak years for human reproduction occur before advanced middle age, and well before older age begins, the forces of selective reproduction cannot exert themselves for Darwinian selection of traits favoring longevity in the evolution for any traits related to longevity per se or physiological sustained function. Hence, there is little evolutionary selection for nutrient requirements to achieve advanced age or for long-term survival. It is more for the preservation of comfort and function for those surviving to advanced age that optimization of nutritional intakes for the elderly would apply, that is for humanitarian and public health importance in the face of the physiological and anatomic changes of senescence.
As early as the 1970s, nutritional scientists advanced the proposition that requirements for different macro- and micronutrients changed with age. A large number of conjectures based on an emerging scientific understanding of senescent physiology have been advanced. It has been suggested that the decreased physical activity and physical conditioning associated with the body composition changes attendant to aging, sets the stage for alterations in requirements in both amounts and relative proportions of protein and the energy-yielding macronutrients. Decreased gastric secretory capacity has a negative influence on the absorption of calcium, iron, and vitamin B12. Changing intestinal motility and digestive function evoked considerations of distinct increases and decreases of nutrients to compensate for the senescence of the intestinal tract, with particular interest in dietary fiber. Attention to compensatory intake for all of the nutrients involved in skeletal mineralization has come to the fore in relation to the recognized tendency to bone mineral loss with advancing age.
The immune and host defense system has been the focus of gerontological nutrition. Increased intakes of both vitamin E and zinc, well above the normally recommended level, have stimulated certain immune functions in studies involving older volunteers. Cognitive function declines with advancing age, and it has even been suggested that adjustment of nutrient intake can favorably affect the retention of memory and cognitive function in older persons. The adequate intake of B-complex vitamins, particularly those related to homocysteine metabolism (vitamin B12, folic acid, vitamin B6, riboflavin), are associated with mental function in older age. It has also been suggested that older individuals need more n-3 fatty acids for preserving cerebral cellular anatomy related to cognition.
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