A longitudinal study of rats chronically exposed to aluminum at human dietary levels.

According to the World Health Organization, oral ingestion of aluminum additives is the main form of aluminum exposure for the general public. Aluminum salts are added to a range of commercially-prepared foods and beverages: to clarify drinking water, make salt free-pouring, color snack/dessert foods, and make baked goods rise. In the present study, six Wistar rats chronically consumed aluminum from 16 months of age to the conclusion of their lifespan (averaging 29.8 months) in an amount (1.5mg/kg bodyweight) equivalent to the high end of the total aluminum range ingested daily by humans living in contemporary urban society. The rats were memory-trained in a continuous rewarded alternation T-maze task and tested weekly from 5 months of age onwards. This longitudinal study compared their mean memory performances over 15 consecutive weeks during middle age (12-23 months) and old age (> or =24 months). Four out of six rats continued to perform the memory task in old age without significant deficit. The remaining two obtained significantly lower mean memory scores in old age than in middle age and exhibited soft signs associated with dementia. Their hippocampal neurons stained for aluminum, showing some but not all features of aluminum accumulation that occur in human hippocampal neurons. In view of evidenced linkages of aluminum with beta-amyloid plaque and neurofibrillary tangle formation in humans with Alzheimer's disease, the findings suggest this protocol is worth testing in larger groups of animals.