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Watercress (Nasturtium officinale R.Br.): A Comprehensive Reference

1. Identity and Botanical Classification

1.1 Botanical Name and Taxonomy

Nasturtium officinale R. Br. (Robert Brown) belongs to the Brassicaceae family, commonly known as watercress. It is a perennial, aquatic, or semiaquatic plant species with creeping or floating stems, which colonizes gently flowing and shallow streams in its natural habitat. It belongs to the Brassicaceae family and is classified by the International Union for Conservation of Nature (IUCN) in the Red List of Threatened Species as a plant of least concern in Europe; however, in Austria and Sweden it is considered an endangered species, while in Poland it is partly endangered.

The plant has been known under various synonyms in botanical literature, including Rorippa nasturtium-aquaticum, Sisymbrium nasturtium, and Radicula nasturtium. Its botanical epithet Nasturtium officinale is derived from the Latin for "twisted or wrinkled nose," a reference to its pungent flavour. The monograph of N. officinale herb is present in the German Commission E Monographs (Phyto-Therapy).

1.2 Natural Source and Growth Habit

Watercress is a rapidly growing, aquatic or semi-aquatic, perennial plant native to Europe and Asia, and one of the oldest known leaf vegetables consumed by humans. It is a perennial species of the Brassicaceae family that grows in and around water. Raw watercress is 95% water, 1% carbohydrates, and 2% protein. In a reference amount of 100 g, raw watercress provides 11 calories of food energy and is a rich source (20% or more of the Daily Value) of vitamin K (208% DV) and vitamin C (48% DV), with moderate amounts (11–18% DV) of vitamin A, manganese, and potassium.

1.3 Common Forms and Preparations

Watercress is consumed and formulated in several forms:

• Fresh herb (raw): Watercress leaves, stems, and fruit can be eaten raw. It is consumed since ancient times in salads, soups, and as an ingredient in savory dishes.
• Cooked preparations: In China, watercress is often boiled alongside pork and traditional medicinal ingredients to make a wintertime tonic soup.
• Standardized extracts: Aqueous, ethanolic, and hydroalcoholic extracts are used in clinical research and supplement manufacturing. Research has used the ethanolic extract of Nasturtium officinale (EENO) and standardized extract of Nasturtium officinale (SENO) in clinical trials, with a dose of 500 mg/day EENO in capsule form used in one placebo-controlled trial.
• Freeze-dried preparations: A partnership between scientists in academia and the food industry has been used to prepare a beverage containing freeze-dried watercress for chemoprevention studies.
• Juice and syrups: Juice preparations have been used in traditional home remedies for respiratory complaints.

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2. Traditional and Historical Use

2.1 Ancient Civilizations

Watercress is one of the earliest cultivated green leafy vegetables. Evidence of consumption by ancient Greeks, Romans, and Persians indicates that it was a common feature of early Mediterranean and Near Eastern diets. Ancient Romans believed watercress provided strength and prevented diseases, making it a dietary staple for their soldiers. Ancient Persians, including King Xerxes, commanded their soldiers to eat watercress to enhance their strength during marches. Though their ancient counterparts knew nothing about mineral content and vitamins, the Persians did observe that soldiers were healthier when watercress was part of their daily diet.

The Greek physician Hippocrates (460–ca. 370 BCE), the "father of medicine," is said to have established a hospital near a stream to ensure easy access to watercress, though this is likely apocryphal. The Roman naturalist and philosopher Pliny the Elder credited this peppery plant with being an effective treatment for anxiety, coughs, and intestinal worms.

2.2 Medieval and Renaissance Use

In the medieval era, watercress was boiled in almond milk and served with cheese during Lent. Up until the Renaissance, watercress was used as a breath freshener and palate cleanser, as well as for medicinal purposes. France pioneered commercial watercress farming in the 17th century near Paris, developing a system of growing it in flowing water beds that mimicked its natural environment.

2.3 Folk Medicine Across Cultures

The traditional medicine of Azerbaijan, Iran, Morocco, and Mauritius, as well as western Asia, India, Europe, and Africa, has made extensive use of watercress. Turkish folk medicine used it as a drug for relieving abdominal pain and as a vegetable added to salads. Iranian traditional medicine administered it as an antidiabetic agent, consumed as an ingredient in juices, salads, or other dishes. As a home remedy, the leaves of watercress have been used as diuretic, depurative, expectorant, odontalgic (toothache-relieving), and hypoglycemic agents. In traditional Iranian medicine, watercress is used to treat diabetes, bronchitis, wound, tuberculosis, influenza, and asthma.

Watercress has been used as an all-purpose medicine for a variety of conditions, including arthritis, asthma, bronchitis, cough, and digestive complaints.

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3. Key Constituents and Active Compounds

3.1 Glucosinolates

The major phytochemicals found in extracts from the different parts (leaves, stems, roots, flowers, and seeds) of watercress are glucosinolates, followed by isothiocyanates, phenolic compounds (mostly flavonoids, phenolic acids, and proanthocyanidins), terpenes (e.g., carotenoids), vitamins (B1, B2, B3, B6, E, and C), and bioelements. There are eight characteristic glucosinolates in watercress: gluconasturtiin, glucobrassicin, glucohirsutin, glucoiberin, glucosiberin, glucotropaeolin, 4-hydroxy-glucobrassicin, and 4-methoxy-glucobrassicin.

Gluconasturtiin is the principal and most studied glucosinolate in watercress. Nasturtium officinale is a cruciferous vegetable rich in gluconasturtiin, the aromatic glucosinolate precursor of phenethyl isothiocyanate (PEITC; 2-phenyl ethyl ITC). Gluconasturtiin is the characteristic major glucosinolate in watercress, in the same way that glucoraphanin is characteristic of broccoli sprouts. The dominant glucosinolate compounds in a UHPLC-DAD-MS/MS profiling study were glucobrassicin and gluconasturtiin.

3.2 Isothiocyanates — PEITC

Watercress contains water-soluble glucosinolates (S-glucopyranosyl thiohydroximates) which are enzymatically hydrolyzed to isothiocyanates — for example, phenethyl isothiocyanate (PEITC) — when the plant tissue is macerated. Whenever this vegetable is disrupted — for instance, during mastication — the enzyme myrosinase (β-thioglucoside glucohydrolase) is released and induces the conversion of gluconasturtiin into PEITC, as well as conversion in the human intestine by microbial myrosinase. PEITC's mechanisms involve inhibitory effects on cytochrome P450 enzymes including human P450s 2A13, 2A6, 1A2, and 2B6, which are catalysts of carcinogen bioactivation.

3.3 Polyphenols and Flavonoids

Fourteen phenolic compounds were identified in watercress leaves, where coumaric acid and its derivatives, caftaric acid, and quercetin derivatives were present in higher amounts. In the roots, a total of 20 compounds were tentatively identified, with coumaric acid and its derivatives, sinapic acid, caftaric acid, and quercetin derivatives as the major phenolic compounds. p-Coumaric acid was the most abundant compound in fresh watercress, followed by quercetin-3-O-sophoroside and isorhamnetin-O-hydroxyferuloylhexoside-O-hexoside. Four kaempferol glycoside derivatives were identified for the first time in this species, and in general, flavonoids predominated over phenolic acids.

3.4 Carotenoids and Fat-Soluble Vitamins

The antioxidants in watercress include carotenoids, chlorophyll, and other polyphenolic compounds. The antioxidant efficacy of watercress is likely augmented by the combined effects of other phytochemicals, such as flavonoids (quercetin, kaempferol, and rutin), phenolic acids, ascorbic acid (vitamin C), carotenoids (β-carotene, lutein, and zeaxanthin), and sulfur-containing compounds. Watercress is also notable for an exceptionally high vitamin K content: in a 100 g reference amount, raw watercress is a rich source of vitamin K (208% DV) and vitamin C (48% DV).

3.5 Minerals and Other Nutrients

Notable mineral and vitamin contributions per 100 g include: calcium 120 mg (9.2% DV), riboflavin 0.12 mg (9.2% DV), copper 77 mcg (8.6% DV), pyridoxine 0.13 mg (7.7% DV), thiamin 0.09 mg (7.5% DV), potassium 330 mg (7% DV), vitamin E 1 mg (6.7% DV), magnesium 21 mg (5% DV), phosphorus 60 mg (4.8% DV), and folate 9 mcg (2.3% DV).

3.6 Key Mechanisms of Action

Phase II enzyme induction via Nrf2: Activated Nrf2 translocates to the nucleus and binds to antioxidant response elements (AREs), triggering the transcription of cytoprotective enzymes such as HO-1, NAD(P)H:quinone oxidoreductase (NQO1), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px), enabling the neutralization of reactive oxygen species before they can initiate lipid peroxidation. Watercress, being a rich source of PEITC, has an important potential role in health outcomes of various chronic disease states, due to its influence on phase II detoxification.

Inhibition of carcinogen-activating CYPs: PEITC decreases the formation of critical reactive metabolites of the tobacco carcinogen NNK, resulting in lower levels of DNA adducts in the lung and decreases in other endpoints, all reflecting inhibition of NNK metabolic activation; these effects are largely attributable to PEITC inhibiting cytochrome P450 enzymes CYP2A13, 2A6, 1A2, and 2B6.

COX-2 and lipoxygenase inhibition: The anti-inflammatory activity of watercress extracts has been tested based on inhibition of 15-lipoxygenase, cyclooxygenase-1, cyclooxygenase-2 (COX-2), and phospholipase A₂.

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4. Scientific Evidence by Area of Use

4.1 Antioxidant Effects and DNA Protection

The best-established area of human clinical evidence for watercress is its antioxidant and DNA-protective activity.

A key trial published in the American Journal of Clinical Nutrition (Gill et al., 2007) demonstrated significant effects in healthy adults. A randomized, controlled trial found that consuming 85 grams of raw watercress daily for eight weeks increased blood levels of lutein (100% increase) and beta-carotene (33% increase) in study participants. The same study also showed reduced lymphocyte DNA damage and altered blood antioxidant status (referenced in multiple systematic reviews as "Gill et al. 2007. Watercress Supplementation in Diet Reduces Lymphocyte DNA Damage and Alters Blood Antioxidant Status in Healthy Adults. American Journal of Clinical Nutrition 85(2):504–510").

A randomized controlled investigation on exercise-induced oxidative stress provided further human data. The study was designed to test the hypothesis that acute (consumption 2 hours before exercise) and chronic (8 weeks consumption) watercress supplementation could attenuate exercise-induced oxidative stress, recruiting ten apparently healthy male subjects (mean age 23 years). The main findings showed an exercise-induced increase in DNA damage and lipid peroxidation over both acute and chronic control supplementation phases, while acute and chronic watercress attenuated DNA damage and lipid peroxidation and decreased H₂O₂ accumulation following exhaustive exercise (P<0.05 vs. control).

A 2025 PRISMA-compliant systematic review of RCTs assessed the totality of evidence. Seven RCTs including 302 patients with a mean age of 47 years (range 23–61) and a mean follow-up time of 39 days (range 21–60) were included. The dosage across trials varied from 85 g/day to 750 mg/kg/day. Antioxidant parameters reported included superoxide dismutase (five studies), ferric-reducing antioxidant power (two studies), glutathione peroxidase (two studies), retinol (two studies), β-carotene (two studies), and α-tocopherol (two studies). The systematic review highlights antioxidant and anti-inflammatory effects of watercress supplementation in randomized controlled trials, noting heterogeneity in WC formulations and dosage.

Evidence strength: Moderate. Multiple small RCTs and one systematic review support antioxidant and DNA-protective effects in humans. Sample sizes are small and follow-up periods short; larger confirmatory trials are needed.

4.2 Cancer Chemoprevention

Watercress and its primary isothiocyanate PEITC have been investigated in multiple human studies for carcinogen detoxification and cancer prevention, particularly in smokers.

In a completed clinical trial, 2-phenethyl isothiocyanate (PEITC) enhanced the detoxification of the environmental toxicants and carcinogens benzene, acrolein, and crotonaldehyde, as determined by increased excretion of the corresponding mercapturic acids in the urine of subjects who took 40 mg of PEITC orally per day. The significant enhancing effect was particularly strong in individuals who were null for the glutathione-S-transferase genes GST-T1, GST-M1, or both.

These results led to the design of a further clinical trial of watercress — a common vegetable that is an abundant and practically unique natural dietary source of PEITC — with a target dose of 40 mg/day of PEITC, the same as in the previous study. When watercress is chewed or otherwise macerated, PEITC is released from its parent constituent gluconasturtiin.

A crossover clinical trial in cigarette smokers also examined PEITC's effects on tobacco carcinogen metabolism. A clinical trial was carried out to determine whether PEITC inhibits the metabolic activation of the tobacco-specific carcinogen NNK in smokers. Cigarette smokers were recruited and randomly assigned to one of two arms — PEITC followed by placebo, or placebo followed by PEITC — taking PEITC at 10 mg in 1 ml of olive oil, four times per day during the one-week treatment period. A significant effect of watercress consumption, as a source of PEITC, on NNK metabolism in smokers was observed in this small clinical study.

Of all isothiocyanates, PEITC is one of the most comprehensively studied in various cancers and has been evaluated in a National Cancer Institute phase II clinical trial to prevent lung cancer in smokers. PEITC is currently being evaluated in two clinical trials: one for evaluating its safety and efficacy profile in head and neck cancer patients (NCT03034603), and another for its long-term effects in cancer patients' outcomes (NCT02468882).

Pharmacokinetic data indicate that in a clinical study in which four healthy subjects were given 100 g of watercress and plasma and urine samples were collected (at time points up to 24 h), PEITC plasma concentrations were determinable, and a one-compartment pharmacokinetic model with first-order absorption and elimination described PEITC pharmacokinetics.

Epidemiological studies have reported an inverse association between cruciferous vegetable consumption and risk of cancers including lung, colorectal, and breast cancers.

Evidence strength: Preliminary to moderate for cancer chemoprevention. Mechanistic plausibility is strong, and several clinical trials in smokers have demonstrated significant carcinogen detoxification effects. Definitive evidence from large randomized trials showing reduced cancer incidence is not yet established.

4.3 Inflammation and Immunomodulation

Several studies have investigated antioxidative, anti-inflammatory, antidiabetic, anti-allergic, antibacterial, hypolipemic, cardioprotective, and anticancer effects of watercress and PEITC; however, most of these effects have been observed in vitro or in animal studies. Only a few human intervention studies have been carried out, and those have mainly focused on antioxidative and anticancer effects. The influence of watercress on the immune system — particularly anti-inflammatory activity — has barely been investigated in human studies.

One human study investigated immunomodulating effects during exercise. Inflammatory blood markers (IL-1β, IL-6, IL-10, TNF-α, MCP-1, MMP-9) were analyzed in whole blood cultures after ex vivo immune cell stimulation. A mild pro-inflammatory reaction was observed after watercress consumption, indicated by an increase in IL-1β, IL-6, and TNF-α, whereas during the recovery phase, watercress consumption led to a stronger anti-inflammatory downregulation of pro-inflammatory cytokines IL-6 and TNF-α. The authors concluded that watercress causes a stronger pro-inflammatory response and anti-inflammatory counter-regulation during and after exercise, and that the clinical relevance of these changes should be verified in future studies.

Evidence strength: Preliminary. Human trials examining inflammation endpoints are limited in number and scope; results show biological activity but are insufficient to draw firm clinical conclusions.

4.4 Cardiovascular Risk Factors and Lipid Profile

Studies have demonstrated that a diet rich in cruciferous vegetables of the Brassicaceae family can reduce the risk of cardiovascular diseases and oxidative stress levels, though previous investigations had demonstrated beneficial effects of watercress on hypercholesterolemia mainly in animal studies.

One randomized, double-blind, placebo-controlled trial investigated lipid effects directly in humans. The study aimed to investigate whether overweight individuals could improve or maintain their serum lipid and oxidative stress markers when given standardized extract of Nasturtium officinale (SENO), conducted over 5 weeks. SENO did not cause a significant statistical change in total serum cholesterol, triacylglycerol, and high-density lipoprotein levels, nor in catalase or superoxide dismutase; however, data suggest SENO positively affected low-density lipoprotein cholesterol profile and lipid peroxidation levels. Further studies were suggested to clarify these results.

A separate study examined watercress in smokers and non-smokers. Watercress consumption reduced total cholesterol and LDL-C levels in smokers and in second-hand smoke-exposed non-smokers; however, HDL-C significantly decreased in SHS-exposed non-smokers. Catalase activity increased, and malondialdehyde levels decreased in all groups. One measure of plasma total antioxidant capacity significantly improved in non-smokers. These findings suggest that watercress consumption may improve lipid profiles and mitigate oxidative stress, though these beneficial effects differ across people with different levels of exposure to cigarette smoke.

A 2026 randomized placebo-controlled pilot study in Thai middle-aged adults examined blood pressure and cardiovascular risk. Watercress is a cruciferous vegetable rich in bioactive compounds that may improve cardiovascular disease (CVD) risk factors; however, clinical evidence regarding its direct impact on CVD risk remains limited. The investigators noted several limitations: the 4-week intervention duration may have been insufficient to fully capture watercress's biological potential, as traditional dietary interventions often require 8–12 weeks to manifest alterations in lipid profiles; the small sample size reduced statistical power; and several interpretations were based mainly on intra-group changes.

Evidence strength: Weak to preliminary. Individual RCTs have produced mixed results on lipid endpoints in humans, and most data showing lipid benefit derive from animal or in vitro studies. Larger, longer trials in defined cardiovascular risk populations are absent.

4.5 Oxidative Stress in Hemodialysis Patients

Two clinical trials have specifically investigated watercress extract in hemodialysis patients, a population with chronically elevated oxidative stress.

A double-blind, placebo-controlled trial explored the effect of the ethanolic extract of Nasturtium officinale (EENO) on antioxidant and biochemical markers. Forty-six hemodialysis patients were randomly recruited to consume either 500 mg/day EENO (n=23) or placebo (n=23) for 4 weeks. It has been reported that watercress supplementation can decrease DNA injury to lymphocytes and modify blood antioxidant status in healthy subjects.

A further trial examined inflammatory markers and vitamin E levels in chronic hemodialysis patients using a hydroalcoholic extract. Watercress (Nasturtium officinale) is a plant rich in vitamins (A, B, C, K, E, and folic acid), ions/elements (iron, chromium, calcium, magnesium, phosphorus, potassium, zinc, and sodium), and bioactive substances (β-carotene, lutein, and quercetin).

Evidence strength: Preliminary. The trials in hemodialysis patients are small and single-site; results are biologically plausible but require replication in larger cohorts.

4.6 Postprandial Glycaemia and Lipid Response

A study assessed the effects of including watercress in a moderately high-fat meal (40% calories from fat) on blood sugar in healthy men, finding that adding 100 grams of watercress to the meal reduced blood sugar after eating. Animal research additionally suggests antidiabetic effects, but human clinical evidence for glycaemic control specifically is very limited.

Evidence strength: Very preliminary for humans. Animal data suggest antidiabetic effects, but clinical trials specifically targeting blood glucose are sparse.

4.7 Ocular Health

Watercress is a dietary source of lutein and zeaxanthin, carotenoids with established roles in eye health. The human macula lutea and eye lens are rich in lutein, zeaxanthin, and meso-zeaxanthin, collectively known as macular xanthophylls, which help maintain eye health and prevent ophthalmic diseases; ocular carotenoids absorb light from the visible region (400–500 nm wavelength), enabling them to protect the retina and lens from potential photochemical damage induced by light exposure. The role of lutein and zeaxanthin in human health, in particular eye health, is well established from epidemiological, clinical, and interventional studies. They constitute the main pigments found in the yellow spot of the human retina, protect the macula from damage by blue light, improve visual acuity, and scavenge harmful reactive oxygen species; they have also been linked with reduced risk of age-related macular degeneration (AMD) and cataracts. The 85 g/day watercress RCT (Gill et al., 2007) demonstrated a 100% increase in blood lutein and a 33% increase in beta-carotene in healthy adults after 8 weeks, consistent with an ability to raise circulating ocular carotenoid concentrations.

Evidence strength: Indirect but plausible. The specific carotenoids in watercress (lutein, zeaxanthin) have strong evidence for ocular protection; direct RCTs linking watercress consumption to AMD or cataract outcomes are not yet available.

4.8 Topical Anti-Inflammatory Applications

Medicinal properties have been attributed to watercress; it contains bioactive phytochemicals with potential anti-inflammatory and antioxidant properties. There is interest in using natural plant products in topical anti-inflammatory applications for the skin, due to relatively low cytotoxicity. Preclinical and early-stage research has examined aqueous watercress extracts for skin inflammation, but robust human clinical data for topical applications remain limited.

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5. Body Systems and Health Areas

• Oncology / Cancer Prevention: Carcinogen detoxification (PEITC-mediated CYP inhibition); antiproliferative and pro-apoptotic effects in preclinical models; phase II NCI trials ongoing for lung and head-and-neck cancer.
• Cardiovascular System: Potential LDL reduction and lipid peroxidation inhibition; antioxidant protection against endothelial oxidative stress; dietary nitrate contribution to vasodilation.
• Metabolic / Glycaemic Control: Preliminary evidence for postprandial glucose reduction; traditional use as antidiabetic agent in Iranian medicine.
• Immune and Inflammatory System: Modulation of COX-2, lipoxygenase, NF-κB, and cytokine pathways (mainly in vitro and animal data); immunomodulatory effects during exercise in one human trial.
• Ocular Health: Lutein and zeaxanthin provision for macular protection and AMD risk reduction (via carotenoid bioavailability data).
• Musculoskeletal / Exercise Recovery: Attenuation of exercise-induced DNA damage and lipid peroxidation in a small RCT.
• Renal System: Antioxidant support in hemodialysis patients; traditional use as diuretic and kidney tonic.
• Respiratory System: Traditional use for bronchitis, cough, and asthma; preclinical data for lung inflammation; used as expectorant in home remedies.
• Skeletal / Bone Health: Exceptionally high vitamin K content (208% DV per 100 g) is relevant to bone metabolism, though no specific watercress RCTs in osteoporosis have been published.

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6. Dosage Forms and Reported Dosages

The following dosages are those reported in published human studies only; they are not recommendations.

• Fresh watercress (whole food): 85 grams of raw watercress daily for 8 weeks, used in the Gill et al. 2007 RCT demonstrating DNA damage reduction and carotenoid elevation.
• Fresh watercress (whole food, single serving): 100 g of watercress given to four healthy subjects in a pharmacokinetic study measuring PEITC plasma concentrations over 24 hours.
• PEITC (isolated compound, not whole watercress): 40 mg of PEITC orally per day was used in the NCI-funded detoxification clinical trial. 10 mg in 1 ml of olive oil, four times per day (total 40 mg/day), was used in the smokers crossover trial.
• Standardized ethanolic extract (EENO) capsules: 500 mg/day EENO in capsule form for 4 weeks, used in the hemodialysis trial.
• Range across 7 RCTs (systematic review): The dosage across seven identified RCTs varied from 85 g/day to 750 mg/kg/day.
• Animal toxicology (preclinical reference only): In acute oral toxicity studies in rats, the estimated LD50 was in the range of 2000–5000 mg/kg. In sub-acute studies, female and male rats were supplemented at doses of 250, 500, and 1000 mg/kg for 28 days.

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7. Safety Considerations and Interactions

7.1 CYP2E1 Inhibition — Chlorzoxazone Interaction

By inhibiting the cytochrome P450 enzyme CYP2E1, compounds in watercress may cause adverse drug interactions in individuals taking certain medications, such as chlorzoxazone (a centrally acting muscle relaxant). This interaction is documented in a published clinical pharmacology study (Leclercq I, Desager JP, Horsmans Y. "Inhibition of chlorzoxazone metabolism, a clinical probe for CYP2E1, by a single ingestion of watercress." Clin Pharmacol Ther 1998;64:144–9). The effects of cruciferous vegetables including Nasturtium officinale, and their isothiocyanate constituents (sulforaphane, PEITC, and indole-3-carbinol) with CYP1A1, 1A2, and 2E1 are discussed in the context of carcinogenesis, induction of beneficial estrogen metabolism, and the ways in which the individual patient's glutathione enzyme systems can alter the efficacy of these vegetables. Due to the difficulties in identifying the active constituents responsible for the modulation of CYP enzymes, prediction of herb-drug metabolic interactions is difficult.

7.2 Vitamin K and Anticoagulant Drugs

Warfarin (Coumadin) is used to slow blood clotting; by helping the blood clot, watercress — through its high vitamin K content — might decrease the effectiveness of warfarin. Given that 100 g of raw watercress provides 208% of the Daily Value for vitamin K (phylloquinone), substantial or variable consumption could affect anticoagulation stability in patients on vitamin K antagonists.

7.3 Gastrointestinal Irritation

Large quantities of watercress may irritate the stomach and intestines.

7.4 Goitrogenic Potential

Theoretical concerns exist about potential goitrogenic effects with long-term, high-dose use due to glucosinolate content, though clinical evidence of this effect in humans is lacking.

7.5 Pregnancy and Lactation

Insufficient safety data exists; therefore, medicinal doses are not recommended during pregnancy or breastfeeding. There is no published information about the use of medicinal-dose watercress preparations during pregnancy or while breastfeeding.

7.6 Contaminants in Wild Watercress

Because watercress grows in or near flowing water, wild or uncultivated watercress can potentially accumulate environmental pollutants or harbor biological contaminants. Cultivated commercial watercress is generally considered safer in this respect. This consideration is separate from the plant's inherent phytochemical safety profile.

7.7 General Toxicology

There is a notable lack of systematic toxicity studies examining doses significantly above the therapeutic range. The maximum tolerated dose and potential toxicity thresholds have not been thoroughly established in clinical research. Animal studies suggest low toxicity even at doses several times higher than therapeutic recommendations, but human data on high-dose administration is sparse. The available clinical data suggest that standardized extract of Nasturtium officinale (SENO) did not cause harm to biochemical parameters in the overweight participants studied.

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References

• Nasturtium officinale Microshoot Culture Multiplied in PlantForm Bioreactor — Phytochemical Profiling and Biological Activity (PMC, 2025)
• Phytochemical and Biological Activity Studies on Nasturtium officinale (Watercress) Microshoot Cultures Grown in RITA® Temporary Immersion Systems (PMC, 2020)
• Nasturtium Officinale — an overview (ScienceDirect Topics)
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• An Aqueous Watercress Extract with Topical Anti-Inflammatory Properties in Inflamed Human Skin (bioRxiv, 2025)
• A Narrative Review on Therapeutic Potentials of Watercress in Human Disorders (PMC, 2021)
• Food as Medicine: Watercress (American Botanical Council / HerbalGram)
• Clinical Trial of Watercress in Detoxification of Environmental Toxicants and Carcinogens (NCI Division of Cancer Prevention)
• Preparation of a Beverage Containing Freeze-Dried Watercress for a Clinical Trial of Carcinogen and Toxicant Detoxification (PMC, 2022)
• Clinical Trial of 2-Phenethyl Isothiocyanate as an Inhibitor of Metabolic Activation of a Tobacco-Specific Lung Carcinogen in Cigarette Smokers (PMC, 2016)
• Pharmacokinetics and Pharmacodynamics of Phenethyl Isothiocyanate: Implications in Breast Cancer Prevention (PMC, 2014)
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• Acute and Chronic Watercress Supplementation Attenuates Exercise-Induced Peripheral Mononuclear Cell DNA Damage and Lipid Peroxidation (PubMed, 2012)
• Evaluating the Anti-Oxidant and Anti-Inflammatory Properties of Watercress Supplementation at Short-Term Follow-Up: A Systematic Review of Randomized Controlled Trials (PMC, 2025)
• Effect of Watercress Extract Supplementation on Lipid Profile and Oxidative Stress Markers in Overweight People with Physical Disability: A Randomized, Double-Blind, and Placebo-Controlled Trial (PubMed, 2021)
• Efficacy of Watercress (Nasturtium officinale R.Br.) Consumption on Blood Pressure, Oxidative Stress Biomarkers, and Estimated Cardiovascular Risk in Thai Middle-Aged Adults: A Randomized Placebo-Controlled Pilot Study (MDPI Antioxidants, 2026)
• Immunomodulating Effect of the Consumption of Watercress (Nasturtium officinale) on Exercise-Induced Inflammation in Humans (PMC, 2021)
• Effects of Nasturtium officinale Extract on Antioxidant and Biochemical Parameters in Hemodialysis Patients: A Randomized Double-Blind Clinical Trial (PMC, 2021)
• The Effect of the Hydroalcoholic Extract of Watercress on the Levels of Protein Carbonyl, Inflammatory Markers, and Vitamin E in Chronic Hemodialysis Patients (PMC, 2021)
• Dietary Sources of Lutein and Zeaxanthin Carotenoids and Their Role in Eye Health (PMC, 2013)
• A Mechanistic Review of β-Carotene, Lutein, and Zeaxanthin in Eye Health and Disease (PMC, 2020)
• Acute and Sub-Acute Oral Toxicity Studies of Standardized Extract of Nasturtium officinale in Wistar Rats (PubMed, 2019)
• Watercress (Wikipedia — Nasturtium officinale)
• Watercress: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews (WebMD/Natural Medicines)