Aside from being a condiment to various foods, horseradish (Armoracia rusticana) root has been traditionally used for coughs and colds for centuries in Europe and parts of Asia. Making a syrup from the distinctively pungent large roots of this plant which grew vigorously at my allotments when I was a herbal student in the UK many years ago, was one of my first experiences with manufacturing a herbal cough medicine, and it is great to now have access to this wonderful herb, grown here in New Zealand.
The source of its pungency and warming aromatic properties, are phytochemicals known as glucosinolates (so-called ‘mustard oil glycosides’) which break down to release volatile and highly bioactive compounds known as isothiocyanates. These act as natural expectorants to encourage mucus elimination, as well as having warming and invigorating actions that can improve the body’s natural defences against unwanted bugs.
Horseradish and its isothiocyanates have been subject to a fair amount of research in recent years, findings from which provide further support for both its traditional as well as potential new applications.
Antimicrobial actions are prominent features of horseradish extracts. Significant antibacterial activity has been shown against a wide range of pathogenic microbes, including bacteria responsible for chest, skin, oral and urinary tract infections(1-6). Isothiocyanates derived from horseradish also exhibit a non-selective antimicrobial activity against several bacterial strains including resistant forms of Haemophilus influenza and E. coli, and yeasts such as Candida albicans(2, 4, 7). The principle isothiocyanate allyl isothiocyanate has synergistic antifungal activity with the drug fluconazole against Candida biofilms(8).
Clinical studies using a combination of horseradish root with nasturtium herb have found it to have comparable efficacy to antibiotics in the treatment of acute sinusitis and acute bronchitis(1). A combination of horseradish with green tea and other herbs has also been reported to have greater efficacy than oseltamivir in preventing H3N2 avian influenza viral transmission(9), suggesting potential antiviral actions.
An excessive host inflammatory response in the lungs is increasingly linked to an unfavourable prognosis when highly pathogenic bacterial or viral infections take hold in the respiratory tract. As such, the anti-inflammatory properties of horseradish and its affinity for the lungs, are probably useful. Diverse anti-inflammatory effects including reduced nitric oxide, tumor necrosis factor-α and interleukin-6 release, and COX-2 expression, have been reported(10-14). Apart from being anti-inflammatory(15), allyl isothiocyanate induces the expression of multidrug resistance-associated protein 1 (MRP1), which plays a protective role against oxidative stress, lung inflammation and progression of chronic obstructive pulmonary disease (COPD)(16).
Other horseradish phytochemicals have also been associated with anti-inflammatory activities in human immune cells. These include inhibition of the cyclooxygenase (COX-2) enzyme, as well as lipoxygenase pathways (PGE2 synthesis and leukotriene LTB4 release)(10, 14). Anti-inflammatory and potential neuroprotective effects, have also been reported recently for hydantoin and thiohydantoin constituents of horseradish(17).
Like many medicinal plants, horseradish is a powerful antioxidant, and recent research suggests a link between its antimicrobial activities, and antioxidant properties(12). An Italian study found fumigation with allyl isothiocyanate to enhance the Vitamin C, polyphenol and flavonoid content of kiwifruit after 120 days of storage, thus improving its antioxidant and potential health benefits(18).
Protection against DNA damage and cell death from oxidative stress, and inhibition of the COX-1 enzyme may also contribute to the reputation of horseradish to protect against various cancers. Isothiocyanates such as allyl isothiocyanate derived from horseradish and other plants such as brasiccas and nasturtium have been increasingly investigated for their anticancer properties in recent years(10, 19, 20, 21). Horseradish flavonoid constituents such as kaempferol and quercetin also seem to help prevent cellular mutations that can lead to cancer(22).
The use of horseradish as a condiment to help digest rich food has been given a tick of approval by Serbian and Austrian research showing powerful spasmolytic (muscle relaxant) effects on the bowel for its isothiocyanates(4, 23). Potential benefits in the management of diabetes type 2 have also been implicated by recent reports that it is a strong inhibitor of the enzyme α-glucosidase, which breaks complex carbohydrates down to glucose(24).
New Zealand grown horseradish is an ideal herb to include in a winter immune tonic, as well as a regular tonic for those who through lifestyle or occupational exposure to various carcinogens, may be at risk of COPD or various cancers. Its affinity for lung conditions in particular, make it a valuable herb to enhance immunity and optimise lung health, during 2020.
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