Geochemical risk factors for mental functioning, based on the Ontario Longitudinal Study of Aging (LSA) .6. The effects of iron on the associations of aluminum and fluoride water concentrations and of pH with mental functioning, based on results obtained from the LSA and from death certificates mentioning dementia

Previous papers in this series noted a positive association between aluminum water concentrations and a measure of mental impairment, and a negative association between fluoride concentrations and the same measure of mental impairment. The results obtained were qualitatively similar to the corresponding associations obtained from death certificate data that list Alzheimer's disease as the underlying cause of death. In addition, the results were also qualitatively similar to the results obtained in a number of other studies carried out at different times, in different areas and using different outcome measures for the measure of mental impairment. The present study concerns the role of iron concentrations and specifically, whether when taking iron concentrations into account, the previously noted associations involving aluminum are maintained. The results show that this seems to be the case and also suggest that iron can compete with aluminum, and can both increase or decrease the likelihood of showing signs of mental impairment. The results do not indicate consistently that by modifying the methods of water purification, using iron instead of aluminum, the treated water will be less biotoxic, although there could be instances, particularly when the aluminum concentrations are relatively high, when the use of iron compounds is beneficial.