Is idiopathic dementia a regional vitamin deficiency state?

We hypothesize that some cases of idiopathic dementia are due to a gradual undernourishment of the brain with water-soluble vitamins. This occurs because the choroid plexus and possibly other transport loci in the central nervous system become unable to transport water-soluble vitamins from blood into the central nervous system in adequate amounts. If this testable hypothesis is correct, direct injections of vitamins into the ventricular cerebrospinal fluid should ameliorate the development of dementia.