The Effects of Zinc on the Olfactory
Neuroepithelium and Olfactory Bulbs of the
Sprague-Dawley Rat Following Oral
Administration of Zinc Gluconate Trihydrate
Anthony Albert Carboni, DEd
Kay J. Cullen, BS
William Gaynor Lavelle, MD
Worcester, MA

The most frequent causes of upper respiratory infections are
human rhinoviruses (HRVs). The olfactory neuroepithelium
(ONe), which includes the mucosa and the receptor cells, is a
first line of defense against airborne viruses and allergens, some
of which manage to penetrate the nasal mucosa and invade the
tissues of the ONe. Biochemical evidence from several studies
suggests that zinc is an effective cold treatment and that overthe-
counter zinc gluconate compounds may provide the high
pharmacological doses of zinc needed to act as the most
effective means of treating and reducing the duration and
severity of symptoms of the common cold. A series of male
Sprague-Dawley rats were fed an oral preparation of zinc
gluconate trihydrate to deliver a comparable dose of ionic zinc,
or received the equivalent through drinking water, to
investigate potential cytotoxic and/or neurotoxic insult from the
use of such compounds to the olfactory receptor cells and other
tissue in the ONe and afferent neuronal pathways. Coronal
sections of the rat ONe and corresponding olfactory bulbs (OB)
showed consistent cellular and tissue damage of increasing
severity that correlated with the duration of treatment with the
zinc compound when compared to the control group animals.
The results of this analysis indicate that the repeated oral
administration of such zinc-containing compounds have
neurotoxic effects on the ONe and to the mitral cells in the OB
of treated rats. These findings point toward increased
investigation into the potential deleterious effects of zinc
containing compounds to humans as well.

http://app.american-rhinologic.org/programs/ARSCOSM2004Rev6.pdf

[
For some time, we've heard that topical ionic zinc preparations (e.g.,
Zicam) can cause anosmia and other damage to the nasopharynx.

But this is the first study I've seen that *oral* zinc (e.g., zinc
lozenges) in high enough dosage to enter the nasopharynx in high
concentation, can be neurotoxic to the nasopharynx as well.
]