First: Why not intranasal zinc (drops, sprays or gels) to treat colds? Such methods seems more logical than lozenges, but intransal zinc application can cause severe intracranial pain, and on rare occassions it can produce a probably irreversable side effect, that being the complete loss of the sense of smell (anosmia).
Second: My clinical research in the early 80s showed that intranasal zinc had no effect on the duration of common colds. How can zinc lozenges be effective? Can't work! Right? Wrong.
Had there not been a Mouth-Nose Biologically Closed Electric Circuit, the cure for the common cold would have been discovered in 1901 (See: Merck. (1901) Part II, Formulas. Manual of the Materia Medica. Merck, New York, p. 125.), and certainly no later than 1923 (See: Merck's Manual of the Materia Medica. New York:Merck and Co. 1923;160). The concept of electron activity resulting in movement of metallic ions outside the nervous system in human physiology is well known in biophysics circles, but is quite foreign to others. The transport of metallic ions long distances through naturally occurring biologically closed electric circuits (BCEC) was described in 1983 in great detail by B. E. W. Nordenström, M.D., of the Karolinska Institute in Stockholm, a member of the Nobel Prize Selection Committee. Regardless of "opinions" of others, these circuits are real and they exert powerful influences in sickness and health.
Among many other findings, Nordenström showed that infected, injured, and cancerous tissues as well as healthy muscles, generate electrical potentials that are not related to nervous system electrical activity. Nordenström clearly showed that metallic ions adhered to the inside of capillaries, thus changing the charge of capillary walls from negative to positive. Consequently, a conduit was provided for other positively charged metallic ions to move long distances. He also showed that Fick's laws of diffusion apply for metallic ions in a bioelectric field.1 His observations suggested a requirement for a BCEC between the mouth and the nose as the explanation for the Zn2+ ion lozenge effect on colds.
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In my research in the late 70s and early 80s, a digital volt-ohm meter was used to discover the flow of electrons in the mouth-nose biologically closed electrical circuit, the only BCEC observable externally in humans. Voltages (60 to 120 millivolts) were measurable only with a digital volt-ohm meter, while electrical resistance were readily measurable with either an analog or digital ohm meter. One terminal was placed within the oral cavity while the other terminal was placed within the nasal cavity. Evidence of the mouth-nose BCEC was also obtained simply by reversing the ohmmeter leads in the mouth and nose. Astonishingly different electrical resistance readings -- showing a strong diode-like effect -- were obtained. Further, I found that people susceptible to colds usually had resistance values in the 1 to 20 Kohm range, with a differential resistance of about 50% of the higher resistance value. People NOT susceptible to colds usually had resistance values in the 100 to 500 Kohm range, with a differential resistance of about 50% of the higher resistance value. These differences suggest that internal nasal electrical resistance, and differential resistances, are a more important indicator of who catches a specific rhinovirus cold than antibody titer to the same virus.
Positively charged Zn2+ ions appear to migrate along preferential pathways between the oral and nasal tissues as well as into other non-oral local tissues and venous and lymphatic drainage pathways. Perhaps some fraction of Zn2+ ions migrates the long distance -- aided by Zn2+ ion-induced capillary membrane pore closure -- from the oral cavity into nasal tissues via preferential pathways in BCEC, and some migrates by mechanical transport. Upon reaching the infected nasal tissues beneath the celia and mucous, Zn2+ ions should provide an antirhinoviral effect, induce interferon production, have an effect on ICAM-1 and dry nasal tissues like they do in vitro.
These findings demonstrate passive absorption (mechanical transport, diffusion, filtration, and osmosis) of Zn2+ ions from mouth into the nose to be aided strongly by electrophoresis. Along with the strong repelling effects of nasal mucus and cilia on foreign substances introduced to the nose, the 60 to 120 millivolt differential repels intranasally introduced Zn2+ ions from mucosal surfaces, explaining inefficacy from nasal sprays or nose drops releasing Zn2+ ions in treating common colds. Additionally, neutrally charged and negatively charged materials introduced into the nasal cavity are directly expelled by action of cilia and mucous, and pass down into the throat.
In the specific case of ZnN- ions introduced directly to the nasal tissue, natural Zn2+ ions resident to the nasal tissue immune system appear to be attracted to and bound by negatively charged exogeneous zinc, thus neutralizing native zinc resulting in worsened colds - theoretically. Examples of worsened colds by negatively charged zinc species from zinc lozenges can be found in Chapter 4.c. of Handbook for Curing the Common cold - The zinc Lozenge Story, published in 1984.