Alliums: giving the immune system a smelly leg up

By February I am generally fed up with the cold and flu season, and this year is no exception.  Our household has been hit hard by a cold/bronchitis 1-2 punch, and we’ve been single-handedly keeping the makers of Ricola and our local Pho (Vietnamese chicken soup) shop financially solvent for the last few weeks.

It’s about this time that I start musing about zinc, antivirals, ICAM-1 inhibitors, VP4 protein based vaccines…in short, why the heck haven’t we found a way to beat the common cold?  I glued together a mouse gene and a jellyfish gene and used it to make polka-dotted green tadpoles last week (there was a sound scientific reason for this, I assure you, but it would take too long to go into here).  Surely we scientists should have a better handle on something that absolutely everybody actually cares about.  Granted, there may be several hundred different serotypes of rhinovirus out there to battle (making a specific vaccine impossible), but it’s hard not to feel like we ought to have made a bit more progress by now.

A close-up of polka-dotted fluorescent green tadpole epithelium. You thought I was making it up, didn't you? If this is fairly routine, where's my common cold cure?

Fortuitously, my attention was led to some new research on the common cold by an unlikely source: the blue flowers popping up in the cracks of my sidewalk.  These are the lovely Ipherion uniflorum (isn’t that a great name? sounds like it’s right out of Tolkien), the blue starflower.

Ipherion uniflorum, the blue starflower. Cousin to culinary alliums like onion, garlic, leeks, and shallots, and a welcome addition to my front yard.

Like garlic and onions, Ipherion is an allium, and like garlic and onions, it smells pungently sulfurous. Discovering this, I went hunting around for more information on the sulfur compounds that give garlic (Allium sativum) its smell, and stumbled into two articles about garlic as a preventative or palliative for the common cold.

Two studies using garlic as a path to a shorter cold:

Both of these are double-blind, placebo-controlled studies.  The first, a single-author study in a fairly obscure journal, came out in the UK 10 years ago. It followed 146 volunteers who took either an allicin-containing garlic supplement or a placebo for 12 weeks.  This study found that volunteers who took garlic got fewer colds (24 vs 65, p<.001), spent fewer total days sick (111 vs 366, p<.001) and were sick for less time per cold (5.01 days vs 1.52, p<.001) than those who took placebo.  Apart from a BBC article the same year and a meta-study (which included only that article) in 2009, there’s been very little follow-up.  This is likely because the author works for the “Garlic Centre” in the UK, so there’s a potential conflict of interest, and because the conclusions are overstated: the abstract says the supplement can “prevent attack by the common cold virus,” which was not shown; volunteers still got colds, and nothing was shown about the mechanism of cold prevention or mitigation.

Still, it’s intriguing, and the new study was also.  This one, also double-blind, placebo controlled, and randomized, was just published in Clinical Nutrition (a journal with reasonable impact; 5-year IF=3.7), and followed 120 initially healthy adults for 90 days.  60 took a supplement containing aged garlic extract (AGE), and 60 took a placebo.  This study found that after 45 days, gammadelta T cells and NK cells from the AGE group had significantly better proliferation than those from placebo (p<.05).  In contrast to the earlier study, this one found that volunteers on AGE supplements were just as likely to get colds as the placebo group.  However, as in the first study, their colds were shorter (61% fewer days sick, p<.001), and less severe, as measured by symptoms reported (21% fewer, p<.001), and days of work or school missed (58% fewer, p=.035).

Garlic (Allium sativum): a stinking rose that's good for your nose? (Photo by JJ Harrison, via Wikipedia).

Do you believe it?

Garlic has been touted as a cure or preventative for a whole bevy of things, like atherosclerosis, hypertension, Alzheimer’s, infections, and even cancer.  The clinical data on all these subjects are mixed, and meta-analyses have been conflated by basically piling up a bunch of weak data and concluding that in aggregate it constitutes good data–poor scientific practice.  At this stage, it’s easy to predict that garlic and the common cold might end up with a similarly conflicted and ambiguous clinical record, as have other common cold remedies like vitamin C, echinacea, and zinc.

However, I have to say the tight error bars on the T cell proliferation assays in this Clinical Nutrition paper were pretty persuasive.  A bevy of questions remain–like what the bioactive molecule in garlic is in this case, whether garlic promotes T and NK cells’ proliferation in vivo or only in culture, whether the extra T and NK cells can be directly linked to a shorter/milder cold prognosis, whether this is a general anti-infection property or limited to particular virus types…etc!  I hope the follow-up is rigorous, because I would happily trade bad breath for shorter colds this time of year.

What say you, scientists?  What kind of studies/data would persuade you that garlic was a legitimate path to a shorter or weaker cold?

Josling, P. (2001). Preventing the common cold with a garlic supplement: A double-blind, placebo-controlled survey Advances in Therapy, 18 (4), 189-193 DOI: 10.1007/BF02850113
Nantz MP, Rowe CA, Muller CE, Creasy RA, Stanilka JM, & Percival SS (2012). Supplementation with aged garlic extract improves both NK and γδ-T cell function and reduces the severity of cold and flu symptoms: A randomized, double-blind, placebo-controlled nutrition intervention. Clinical nutrition (Edinburgh, Scotland) PMID: 22280901


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