From the conspiracy analysts:

Fluoride, administered daily via your gums and mouth, in the form of toothpaste along with the unregulated doses found in some public drinking water, which itself is used to manufacture and process many foodstuff has been demonstrated in autopsies to accumulate in and around the Pineal Gland, rendering it dead and inoperative, Fluoride accumulates over your lifetime and is believed by some to be a major contributor to mental decline in the elderly.

It is also thought to interact with Aluminium, found in many antiperspirants and everyday ally cookware, which enters the body in a sustained and regular way via our regular habits.

Fluoride and aluminium https://pubmed.ncbi.nlm.nih.gov/30868981/ Aluminium and fluoride in drinking water in relation to later dementia risk