Subscribe to the OSS Weekly Newsletter!

Register for the OSS 25th Anniversary Event

Wasabi-More than Just a Sushi Condiment?

Since I’m plagued by a fish allergy, sushi is off the table. It would probably be off anyway, as I don’t find eating raw fish particularly appealing. Abstaining from sushi also means not indulging in wasabi. But I’m quite happy to indulge in the chemistry of wasabi, which has some interesting features.

Wasabi, or “Japanese horseradish,” is a plant in the same family as broccoli, cabbage, mustard, Brussels sprouts, kale, cauliflower and regular horseradish. The common feature here is that these “brassica” plants all contain compounds called glucosinolates and an enzyme, myrosinase that do not come into contact with each other until the plants or their roots are crushed. The chemical reaction that then ensues results in the formation of isothiocyanates, a group of compounds that, at least in the laboratory, have some interesting anti-cancer effects. They induce the formation of enzymes, some of which have antioxidant properties and others that help remove carcinogens from the body. Along with this, other enzymes that play a role in inflammation are suppressed and the production of inflammatory cytokines is reduced. Isothiocyanates are also responsible for the brassicas’ pungency and nasal irritation. And maybe for their memory and hair-growing effects. But double underline that “maybe!” 

Dietary patterns like the Mediterranean diet with their emphasis on lots of fruit and vegetables have been linked with improved cognition, a precept also supported by a preliminary trial with sulforaphane, an isothiocyanate in broccoli. This prompted Japanese researchers to turn to wasabi and investigate any potential memory enhancement effects since crushing the underground stem, or rhizome, of wasabi gives rise to an especially high concentration of isothiocyanates, in particular a very stable one with the foreboding name, 6-methylsulfinylhexyl isothiocyanate (6-MSITC). 

Seventy-two subjects aged between 60-80 were treated either with a 6-MSITC supplement or a placebo for twelve weeks in a double-blind, randomized trial. Before and after the experiment they underwent a battery of twelve tests that measure various aspects of cognition. Eight of these tests revealed no difference between the experimental and placebo groups, but on four tests involving the learning and retaining of new information, the wasabi takers did a tad better. That was enough to generate headlines like “Spicing up memory: Wasabi found to boost brainpower in seniors.” There’s some poetic license taken here. A more realistic headline would be: “High doses of a chemical found in wasabi taken in a supplement form may marginally improve memory on some tests.” 

There are also some of troublesome issues with this study. It was published in “Nutrients,” not exactly a high-powered journal, and funded by the Kinjirushi Company, that, surprise, surprise, produces wasabi. Of course, that doesn’t invalidate the results, but one does wonder about the extent of data mining that was involved to generate some sort of a positive finding. While “boosting” of memory may be an overstatement, the study did boost the sale of wasabi supplements, of which there is a large variety. As with most dietary supplements, what these actually contain is anyone’s guess. I am inclined to say that this memory study is not memorable. 

Neither is a study about 6-MSITC that suggests the chemical stimulates hair growth. This one was not only funded by Kinjirushi, it was carried out by its own researchers. “Wasabi found to promote hair growth three times faster than minoxidil,” blared one headline describing the study. To start with, the researchers did not measure hair growth. No human heads or hair were involved. Whatever happened, took place in a lab with cultured cells. The cells in question are dermal papilla cells, one type of cell found in the hair follicle, the tiny cavity in the skin from which a hair grows.  

Proliferation of dermal papilla cells is one factor that determines hair growth, and indeed minoxidil, which has been demonstrated to grow hair, does cause such proliferation. That makes the finding about wasabi causing such an effect interesting but not something to crow about. At least not very loudly. That’s because while minoxidil can stimulate hair growth, it does this rather ineffectively, and whether the effect is due to dermal papilla cell proliferation is unclear. There is no point to rubbing wasabi on a bald head. But maybe the Kinjirushi scientists can contemplate a study with some sort of application of 6-MSITC to scalps with thinning hair.  

The pungency of the isothiocyanates might well be a problem faced by the researchers since walking around with a head reeking of wasabi may not be an appealing feature of the treatment. That irritating scent, however, was exactly what Makoto Imai and colleagues at Japan’s Shiga University of Medical Science found appealing. They developed a “wasabi alarm” that dispenses a spray of allyl isothiocyanate, one of the nasal irritants in wasabi, to wake people who are hard of hearing in case of fire. Smoke detectors are designed to wake people with their piercing wail, but you have to be able to hear the sound. The Shiga scientists, aware that the intense irritation caused by a concentrated wasabi essence can wake all but the dead, engineered a device that wired a standard smoke detector to a can of the essence.  


Back to top