Trace Element Levels and Cognitive Function in Rural Elderly Chinese

Trace elements are chemical elements that are needed in minute quantities for the proper growth, development, and physiology of the human organism. Trace elements are routinely involved in metabolic processes and oxidation-reduction reactions in the central nervous system (CNS) and could have a possible effect on cognitive function. For example, elevated lead levels are shown to be associated with alterations in ionic, cholinergic, and dopaminergic neurotransmission in the CNS (1). Iron is necessary to ensure oxygenation and to produce energy in the cerebral parenchyma and for the synthesis of neurotransmitters and myelin (2). Whereas calcium is hypothesized to impact brain dopamine synthesis (3), copper’s impact on cognition is believed to be its interaction with amyloid-β (Aβ) peptide by causing Aβ aggregation in the brain (4). The relationship between trace elements measured in dietary intake or in drinking water and cognitive function in elderly persons has been examined previously. Results of the effect of aluminum on cognitive function or Alzheimer’s disease were inconsistent (5,6). There were reports of a positive relationship between cognitive function and dietary intake of zinc and iron in healthy elderly adults (7), but no associations were found when zinc and iron were measured in drinking water (8,9). Dietary copper intake in persons with high saturated and trans fat was found to be a risk factor for cognitive decline (10), and calcium levels in drinking water have a positive association with cognitive function (8,9). It is recognized that trace element levels measured in dietary intake based on food frequency questionnaire may not take into account plant soil variation for certain elements, and that elements measured in drinking water may not accurately reflect trace element levels in each individual. Biochemical measures from individuals are preferred measures of trace elements. However, in studies of populations from developed countries, biological measures of trace element levels often reflect intake from multivitamin supplements, which may be confounded by health conditions and socioeconomic status of the individuals. The rural elderly Chinese population represents an opportunity for studying the relationship between trace element levels and cognitive function. The rural Chinese are unusually stable with most living in the same village throughout their entire life and consuming food that is locally grown. In addition, it is rare for these villagers to take dietary supplements. In this article we report the association between seven trace element levels measured in plasma samples and cognitive function in a study of elderly Chinese persons.