Benefits
Traditional support for the urinary tract
A fixed combination of horseradish root and nasturtium has been studied in adults prone to repeated urinary tract infections. Over 90 days the combination group averaged fewer confirmed new episodes than placebo, a small but statistically significant difference. The trial tested the two-herb product, not horseradish on its own, and was linked to the maker.
Traditional support for the respiratory tract
In a placebo-controlled trial, adults took the horseradish-and-nasturtium combination for up to 84 days while new respiratory infections were counted. The higher-dose group had a lower rate of new infections than placebo, with the lower dose in between. This measured a fixed combination product, not horseradish alone, and was linked to the maker.
Observed in everyday-practice comparison studies
Two large German observational studies let doctors choose the horseradish-and-nasturtium combination or standard antibiotics for acute sinus, bronchial or urinary complaints. Symptom scores fell by similar amounts in both, and fewer side effects were recorded with the herbal product. These were not randomized, the groups differed at the start, and they were run by the maker.
Source of sinigrin and allyl isothiocyanate
Horseradish root is a concentrated source of the glucosinolate sinigrin. When the root is grated or chewed, the plant enzyme myrosinase releases allyl isothiocyanate, the pungent mustard oil, along with smaller amounts of phenethyl isothiocyanate. Laboratory analyses confirm these compounds account for the root's sharp taste and smell.
Mustard oils slow bacterial growth in the laboratory
In test-tube studies, the isothiocyanates from the horseradish-and-nasturtium combination inhibited the growth of a range of bacteria, including common airway and urinary organisms and some antibiotic-resistant strains. These are laboratory findings on isolated bacteria, not evidence of an effect on infections in the body.
Mechanism of action
Sinigrin becomes allyl isothiocyanate when the root is cut
In the intact root, sinigrin and the enzyme myrosinase are kept apart. Grating, chewing or crushing brings them together, and myrosinase converts sinigrin into allyl isothiocyanate. Heat and long storage inactivate myrosinase and lower how much mustard oil forms, so cooked horseradish is far less pungent.
Volatile mustard oils reach the airways and urinary tract
The active isothiocyanates are volatile, and after being absorbed from the gut they are partly carried out through the lungs and the urine. This is the traditional rationale for using horseradish for the respiratory and urinary tract, where the compounds come into contact with the lining. It rests on how the oils are handled, not on proven clinical effects.
Isothiocyanates inhibit bacteria in laboratory tests
In plated-bacteria and agar-dilution experiments, the isothiocyanates from the combination stopped or slowed the growth of gram-positive and gram-negative bacteria and some fungi, with resistant and non-resistant strains similarly affected. Whether these concentrations are reached at the site of an infection in people is not established.
Cell-signaling pathways in laboratory studies
In laboratory studies, allyl and related isothiocyanates influence cell-signaling pathways such as Nrf2, which switches on antioxidant and detoxification enzymes, and NF-kB, which drives inflammation. These are cell-level findings and have not been shown as clinical outcomes from oral horseradish in people.
Clinical trials
Randomized, double-blind, placebo-controlled trial of a horseradish root and nasturtium herbal combination taken twice daily for 90 days to prevent recurrent urinary tract infections. (Albrecht et al. 2007, Curr Med Res Opin)
174 adults aged 18 to 75 with chronically recurrent lower urinary tract infections (per-protocol analysis).
The combination group averaged 0.43 confirmed recurrent infections over the 90 days versus 0.77 on placebo, a statistically significant difference (p = 0.035). Adverse events were similar in the two groups. The trial tested a fixed two-herb product, not horseradish alone, and was carried out by a maker-linked group.
Randomized, double-blind, double-dummy, placebo-controlled phase III trial of two doses of a horseradish root and nasturtium combination for up to 84 days to prevent new respiratory tract infections. (Fintelmann et al. 2012, Curr Med Res Opin)
351 adults aged 18 to 75 randomized to higher-dose combination, lower-dose combination or placebo.
Excluding infections in the first 7 days, new-infection rates were 13.3% on the higher dose, 18.4% on the lower dose and 25.6% on placebo; the dose trend was significant (p = 0.0171, intention-to-treat). The character, intensity and duration of infections did not differ. A fixed combination product, maker-linked.
Prospective, non-randomized cohort study in which physicians chose the horseradish and nasturtium combination or standard antibiotics for acute sinusitis, bronchitis or urinary tract infection. (Goos et al. 2006, Arzneimittelforschung)
1,649 patients aged 4 and over in Germany (1,223 combination, 426 antibiotics).
Average symptom scores fell by about 78 to 81% with the combination and 80 to 88% with antibiotics; the combination met a non-inferiority margin for sinusitis and bronchitis but fell just short for urinary tract infection. Adverse events were recorded in 1.5% of combination versus 6.8% of antibiotic patients. Not randomized and maker-run.
Prospective, non-randomized cohort study comparing the horseradish and nasturtium combination with a standard antibiotic for acute sinusitis, bronchitis or urinary tract infection, chosen by the physician. (Goos et al. 2007, Arzneimittelforschung)
858 children and adolescents aged 4 to 18 in Germany (523 combination, 335 antibiotic).
Symptom scores fell by about 85% in both groups and were judged equivalent, but the combination group was less severely affected at the start, so the groups were not comparable. Adverse events were recorded in 0.6% of combination versus 3.9% of antibiotic patients. Observational and maker-run.
Laboratory study measuring the antibacterial activity of the volatile mustard oils from the combination against 13 bacterial species using a sealed gas-diffusion test. (Conrad et al. 2006, Arzneimittelforschung)
Bacterial isolates in the laboratory (20 isolates each of 13 species), not people.
The combined mustard oils inhibited common airway and urinary organisms, including Haemophilus influenzae, Moraxella catarrhalis, Escherichia coli, Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus. A test-tube study of isolated bacteria, with no measure of effect in the body.
Laboratory susceptibility study of a mixture of benzyl, allyl and phenethyl isothiocyanates, in the proportions found in the licensed combination, against bacterial and fungal pathogens. (Conrad et al. 2013, Drug Res (Stuttg))
Clinically relevant bacteria and Candida species in the laboratory, including antibiotic-resistant isolates.
Minimum inhibitory concentrations varied widely by organism; Haemophilus influenzae, Moraxella catarrhalis and Candida were highly susceptible, while several others were only moderately so. Resistant and non-resistant bacteria were similarly susceptible. A laboratory study, not a measure of clinical benefit.