Losing Your Sense of Smell

792px-Nostrils_by_David_Shankbone-300x227Think about the last time you had a bad cold and couldn't smell.  Not only did your own voice sound funny inside your head, but you probably lost your appetite, at least for a bit.  That's because our sense of smell, conveyed by the only neurons we have that are directly exposed to our outside environment, are found at the top of the nose, and they are intimately connected to our sense of taste.  When they're all glued up with sticky mucus they don't work.  Thus one of the fundamental ways we can enjoy food, by smelling it, is disabled, and most of us consume less. 

While for some, eating less may sound like a welcome change, over time it leads to malnutrition and loss of muscle mass.  As Rick points out in the podcast, loss of smell, known in medical vernacular as 'anosmia,' also is unsafe, since we can't detect things like leaking natural gas, gasoline fumes or other potential ingition hazards, nor can we tell when food is rotten and shouldn't be consumed.  So using an over-the-counter cold remedy associated with a permanent loss of smell is probably not a good idea.

That's the conclusion of a much more rigorous study published in this issue of Archives of Otolaryngology, Head and Neck Surgery: The Bradford-Hill Criteria and Zinc-Induced Anosmia.   Investigators used a set of standards developed for establishing the link between cigarette smoking and lung cancer to nail down the link between application of a gel containing zinc gluconate, a homeopathic remedy for colds, and loss of smelling ability in 25 patients.

Anyone who's listened to our podcast will no doubt be asking, why are we looking at a study that doesn't meet the gold standard criteria of double-blind, prospective, placebo-controlled, and let us not forget, randomized and long term?  In this case that's unethical.  Imagine saying to your prospective study participants, hey, how about using this gel in your nose next time you think you're getting a cold so we can assess whether you lose your sense of smell permanently?  Hmmm.  Recruitment and retention may be challenging.

Instead investigators applied the Bradford-Hill criteria to circumstances related to loss of smell for those unfortunate enough to have experienced it.  These include plausibility of the association, strength of the association, consistency and others.  Sure enough, they conclude, using this preparation is causative with regard to permanent loss of smell.  As the FDA has already taken one very popular preparation of zinc off the market, perhaps fewer people are likely to be exposed to the possibility.  But Rick points out in the podcast that the FDA isn't empowered to regulate many homeopathic or 'natural' remedies, supplements and the like, so the risk is still there.  Take home message:  avoid zinc preparations in your nose.  Other studies that have looked at their ability to decrease duration of viral shedding or improve cold symptoms have come up empty-handed, so best not to use something with no upside but significant potential for harm.

Other topics this week include delaying surgery for anterior cruciate ligament tears in NEJM, good news about the whooping cough vaccine in Pediatrics, and more data on statins and cholesterol from the JUPITER trial in the Lancet.  Until next week, y'all live well.

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