With spring upon us, the New Zealand countryside and our gardens are rich with budding and flowering plants, many of them normally regarded as weeds, but in fact highly medicinal.
One of these is Nasturtium (Tropaelum majus; Indian cress), a plant with water lily like circular leaves and bright yellow, orange and red flowers which is native to South America but established in many warmer areas of New Zealand and Australia. While it can certainly be very weedy in some situations, it also makes a useful plant on the edges of the vegetable garden to attract bees and other beneficial insects. It can also act as a decoy by attracting cabbage white butterflies and drawing these pests away from brassicas.
What many people don’t realise, however, is that all parts of Nasturtium are edible, with its leaves and flowers making a decorative, peppery addition to salads, and the fruits when pickled with vinegar serving as a tasty alternative to capers. It also has outstanding antioxidant activity due to its rich content of phenolic compounds, including anthocyanin and vitamin C. Like many ‘weeds’ readily available in the New Zealand environment, Nasturtium is also a highly medicinal plant.
Traditionally it was used to help ward off and treat various infections, particularly those affecting the lungs and the urinary tract. The pungent compounds known as isothiocyanates found in all parts of nasturtium and roots of horseradish (Armoracia rusticana), have powerful and fairly broad spectrum antibacterial activities particularly against Haemophilus influenza and Moraxella catarrhalis, a common cause of middle ear infection (otitis media) and sinusitus in children(1). These isothiocyanates have also recently been reported to have good activity against both developing and mature biofilms of Pseudomonas aeruginosa, a bacterial pathogen associated with many serious human illnesses(2). Importantly also, they have also been shown to be well absorbed into the bloodstream following oral ingestion of nasturtium in humans(3).
Nasturtium was used in folk medicine as a remedy against scurvy, and can be used as a natural, warming remedy to help the body overcome and prevent the common cold and influenza. It was also used traditionally to treat muscular pain, and it’s antimicrobial properties extend to its use as a topical treatment for bacterial infections and minor scrapes and cuts.
Possible applications in the prevention or treatment of various cancers are also likely, due to conversion of a key constituent glucotropaeolin to benzyl isothiocyanate, within the body. This compound, formed also from isothiocyanates found in brassica (cruciferous) vegetables, exhibits anticancer activity against cultured lung, breast, liver, prostate, brain, melanoma, oral & ovarian cancer cells in vitro, and prevents chemically induced carcinogenesis in rodents(4-10).
Potential benefits in fluid retention, hypertension and other cardiovascular conditions, have been suggested by Brazilian research showing diuretic, hypotensive and lipid-lowering activities for a hydroethanolic extract in rats(11-13). Angiotensin converting enzyme (ACE) inhibition was implicated as a possible mechanism for these effects, in a similar manner to how ACE inhibitor drugs work to help manage hypertension and other cardiovascular conditions(14). Unlike many other conventional diuretic drugs, however, no unwanted effects on urinary calcium or potassium excretion seem to occur, suggesting valuable potassium and calcium-sparing properties. These findings indicate possible applications also to help prevent osteoporosis, which is supported by another Brazilian study in menopausal rats(13).
Nasturtium may also be useful to help prevent or manage obesity, according to findings from a Korean study published in the June 2017 issue of the journal Food and Nutrition Research(15). The study investigated the effects of a nasturtium ethanolic extract on a mouse cell line with adipocyte-like characteristics, used in research on adipose (fat) tissue. Treatment of cells with nasturtium extract produced a concentration-dependent reduction in lipid accumulation, and inhibited the expression of various proteins associated with differentiation of fat cells. This suggests potential usefulness also, in the prevention and treatment of obesity.
With these compelling research findings, incorporation of nasturtium into the diet or herbal treatments of a range of human conditions common in the 21st century, should overtake our view of it simply as a bothersome weed.
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