Synthetic zeolite is not safe to ingest in the long term because it releases aluminium into the body where it can accumulate. This does not occur with natural zeolite.
It states in the Critical Review on Zeolite Clinoptilolite Safety and Medical Applications in vivo:
“ … aluminum from the clinoptilolite materials does not enter the blood or accumulate in the body …”
“… aluminum released into systemic circulation was observed only in rats supplemented with synthetic zeolite A. The latter effect was attributed to the zeolite A lower stability in the acidic pH relevant for the human intestine in comparison to clinoptilolite materials.”
“In this study, authors also proved that clinoptilolite materials were efficient in the removal of aluminum from aluminum chloride-intoxicated rats in vivo. These observations may be attributed to the clinoptilolite stability …”