Aluminum is the third most abundant element in the Earth's crust. It is normal to find it in our drinking water, in our soil, and in our food (both naturally occurring and added.) It is a common additive in everything from flour to antiperspirant.

Sources: http://www.atsdr.cdc.gov/toxprofiles/tp22-c2.pdf http://www.atsdr.cdc.gov/toxprofiles/tp22-c1-b.pdf

It is difficult to do a full, double blinded study due to those outside influences. Numerous studies have been done on patients with reduced renal function who accumulated aluminum as a result of long-term intravenous hemodialysis therapy with aluminum-contaminated dialysis fluid and, in many cases, concurrent administration of high oral doses of aluminum to regulate phosphate levels (i.e., reduce uptake of phosphate by binding it in the gut) and have limited usefulness in predicting toxicity in the general population because the very large aluminum exposure levels and impaired renal function results in aluminum accumulation.

Animal studies have shown that doses of greater than 200mg a day for over a long duration can lead to Dialysis encephalopathy. Dialysis encephalopathy is a degenerative neurological syndrome, characterized by the gradual loss of motor, speech, and cognitive functions. The idea that aluminum causes Alzheimer’s disease is incorrect. It has been debunked by numerous peer reviews of the data.

Over-all, the miniscule amount of aluminum in a vaccine is completely overshadowed by simply living on the planet.