Watercress: one good trial, and a parasite risk in raw leaves

The strongest human data on watercress comes from one single-blind crossover trial in 60 adults, 30 of them smokers. Eating 3 oz (85 g) of raw watercress a day on top of their usual diet for 8 weeks went with 17 percent less basal DNA damage in white blood cells and 23.9 percent less oxidative purine damage. Those are lab markers from a comet assay, and the trial did not look at cancer. In the same people plasma lutein doubled and beta-carotene rose by 33 percent. The changes were larger in smokers, though the abstract gives no number for that gap. A single meal is a different story. When 16 healthy young men ate 3.5 oz (100 g) of watercress with a high-fat meal, their triglycerides, cholesterol, IL-6 and TNF-alpha over the next 4 hours did not differ significantly from a control meal. Neither the US rules nor the EU register holds any health claim for watercress by name.

The numbers, per 3.5 oz (100 g)

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• A cup of raw watercress weighs about 1.2 oz (34 g) and carries about 85 ug of vitamin K (250 ug per 3.5 oz (100 g)) and 14.6 mg of vitamin C. — US survey food Watercress, raw Evidence E source
  1 cup 34 g: vitamin K 85 ug, vitamin C 14.6 mg; per 3.5 oz (100 g) 250 ug and 43 mg

What a real portion looks like

• The US survey table lists cooked watercress at 31.3 mg vitamin C per 3.5 oz (100 g) against 43 mg raw, while a cooked cup of 5 oz (142 g) holds far more leaf than a raw cup of 1.2 oz (34 g). — US survey foods Watercress, cooked and raw Evidence E source
  Vitamin C 31.3 vs 43 mg/100 g; vitamin K 262.5 vs 250 ug/100 g; 1 cup cooked 142 g vs raw 34 g

What your body absorbs

• In 10 men, calcium absorption from watercress soup was 27.4%, against 45.5% from skim milk, measured with a double stable isotope. — 10 male volunteers, single labeled meals (n = 10) Evidence B source
  Fractional Ca absorption 27.4% (SEM 1.9) watercress soup vs 45.5% (SEM 1.9) skim milk vs 35.7% Ca-enriched milk

What cooking and storage change

• A Danish woman got liver fluke infection from raw watercress picked in a meadow with grazing sheep, and the authors warn about eating raw wild green plants. — One 64-year-old woman, Denmark (n = 1) Evidence D source
  Liver fluke infection resolved with triclabendazole

What it does to your health

• In a crossover RCT in 60 adults, 3 oz (85 g) of raw watercress a day for 8 weeks cut basal lymphocyte DNA damage by 17% and oxidative purine damage by 23.9%. — 30 men and 30 women (30 smokers, 30 nonsmokers), mean age 33, range 19-55, 8 weeks (n = 60) Evidence B source
  Basal DNA damage -17% (P = 0.03); basal plus oxidative purine damage -23.9% (P = 0.002); H2O2-challenged damage -9.4% (P = 0.07)
• Adding 3.5 oz (100 g) of watercress to a high-fat meal did not change blood triglycerides, cholesterol, IL-6 or TNF-alpha over 4 hours in 16 healthy young men. — 16 healthy men aged 20-30, single test meals 1 week apart (n = 16) Evidence B source
  No significant difference in TG, total, HDL or LDL cholesterol, IL-6 or TNF-alpha vs control meal

Safety, limits and interactions

• In 7 volunteers, 1.8 oz (50 g) of watercress homogenate taken 10 hours before 1 g acetaminophen lowered the oxidative Cys-acetaminophen metabolite curve by 28%. — Human volunteers, single 1 g acetaminophen dose after 50 g watercress homogenate (n = 7) Evidence C source
  Cys-acetaminophen AUC -28% (SE 3%), peak -21% (SE 4%); parent drug and glucuronide unchanged
• People on warfarin should keep vitamin K intake steady, since sudden changes can raise or lower the anticoagulant effect, which matters for a vitamin K rich leaf like watercress. — People taking warfarin and similar anticoagulants Evidence E source
  —
• Among 616 fasciolosis patients in central France over 28 years, watercress was the source of infection in 98%. — 616 patients with fasciolosis, Limousin, central France, 1955-1998 (n = 616) Evidence C source
  Watercress as infection mode in 98%
• Two men in northern California caught liver fluke infection after eating watercress together, with fever, eosinophilia and liver lesions two months later. — Two adult men, Marin County, California (n = 2) Evidence D source
  Febrile illness, eosinophilia, liver lesions; treated with triclabendazole

What people believe that the data does not support

• Neither regulator has ruled on watercress by name: 21 CFR part 101 does not mention it and the EU health claims register holds no claim under this name. — US 21 CFR part 101 and the EU register of 2330 claims, searched for watercress (n = 0 claims in each register) Evidence E source
  No authorized, rejected or pending claim for watercress

Who this works differently for

• In the same 8-week RCT, 3 oz (85 g) of watercress a day doubled plasma lutein and raised beta-carotene by 33%, and the benefits were larger in smokers than in nonsmokers. — 30 smokers and 30 nonsmokers, 19-55 years, 8 weeks (n = 60) Evidence B source
  Plasma lutein +100%, beta-carotene +33% (P < 0.001); larger changes in smokers

What is still unknown

• A meta-analysis of 23 dietary trials, watercress among the vegetables tested, found cruciferous diets raise CYP1A2 activity by 20-40%, though clinical relevance for drug users stays unclear. — Human dietary intervention trials with drug-metabolism end points (n = 23 trials) Evidence C source
  CYP1A2 activity +20-40%; GST-alpha +15-35%

The bottom line

A cup of raw watercress is light, about 34 g, and the US survey table gives it roughly 85 ug of vitamin K and 14.6 mg of vitamin C. A cooked cup packs 5 oz (142 g) of leaf. The same table lists 31.3 mg of vitamin C per 3.5 oz (100 g) cooked against 43 mg raw, and those cooked figures are calculations that nobody measured on watercress itself. As a calcium source it trails milk. In a small 1989 study of 10 men, with an isotope label added to the food, 27.4 percent of the calcium in watercress soup was absorbed, against 45.5 percent from skim milk. Raw watercress can carry a liver fluke parasite. Among 616 liver fluke patients in central France between 1955 and 1998, watercress was the source of infection in 98 percent. Single cases turn up elsewhere: two men in California who ate watercress together, and a Danish woman who picked it raw in a meadow grazed by sheep. Her doctors warn against eating raw green plants gathered in nature. If you take warfarin, the NIH Office of Dietary Supplements advises keeping vitamin K intake steady, and watercress is rich in it, so the point is a consistent intake, without sudden changes. In 7 volunteers, 1.8 oz (50 g) of watercress homogenate taken 10 hours before 1 g of acetaminophen lowered one oxidative metabolite curve by 28 percent. Whether that changes anything clinically was not tested. A meta-analysis of 23 dietary trials found that cruciferous vegetables, watercress among them, raise the drug-metabolizing enzyme CYP1A2 by 20 to 40 percent, and its authors call the clinical significance unclear. We found no study of watercress in pregnancy, children or kidney disease.

Sources

1. wcr-daily-r8-11 · dataset
   Watercress, raw, WWEIA category Other dark green vegetables, fdc_id 2709639: 1 cup 34 g; 1 sprig 2.5 g; Vitamin K (phylloquinone) 250 UG per 100 g; Vitamin C, total ascorbic acid 43 MG per 100 g
   USDA FoodData Central, FNDDS survey foods, release 2024-10-31 · checked 2026-09-29
2. wcr-daily-r8-12 · dataset
   Watercress, cooked, fdc_id 2709640: 1 cup 142 g; Vitamin C, total ascorbic acid 31.3 MG per 100 g; Vitamin K (phylloquinone) 262.5 UG per 100 g. Watercress, raw, fdc_id 2709639: Vitamin C 43 MG per 100 g
   USDA FoodData Central, FNDDS survey foods, release 2024-10-31 · checked 2026-09-29
3. wcr-daily-r8-04 · absorption trial
   Mean percentage absorption was 45.5 (SEM 1.9)% from the skimmed milk, 35.7 (SEM 4.7)% from the Ca-enriched milk and 27.4 (SEM 1.9)% from the watercress soup.
   Br J Nutr, 1989 · checked 2026-09-29
4. wcr-daily-r8-10 · case report
   On several occasions, she had been eating watercress from a meadow with grazing sheep. The tendency of eating raw watercress and other green plants collected in nature confers an increased risk of developing liver fluke infections.
   Ugeskr Laeger, 2018 · checked 2026-09-29
5. wcr-daily-r8-01 · crossover RCT
   The subjects were fed 85 g raw watercress daily for 8 wk in addition to their habitual diet. ... Watercress supplementation (active compared with control phase) was associated with reductions in basal DNA damage (by 17%; P = 0.03), in basal plus oxidative purine DNA damage (by 23.9%; P = 0.002), and in basal DNA damage in response to ex vivo hydrogen peroxide challenge (by 9.4%; P = 0.07).
   Am J Clin Nutr, 2007 · checked 2026-09-29
6. wcr-daily-r8-03 · crossover RCT
   Lettuce and watercress were added to the test meal in portions of 100 g and cellulose was added to the control meal. ... Notably, plasma TG, total cholesterol, HDL-C, and LDL-C had no significant differences among the meals. Moreover, the levels of plasma IL-6 and TNF-α did not differ among the meals.
   Lipids Health Dis, 2021 · checked 2026-09-29
7. wcr-daily-r8-06 · crossover trial
   A single oral dose of acetaminophen (1 gm) was given 10 hours after ingestion of watercress homogenates (50 gm). In comparison with acetaminophen only, the ingestion of watercress resulted in a significant reduction in the area under the plasma cysteine acetaminophen (Cys-acetaminophen) concentration-time curve and in the peak plasma Cys-acetaminophen concentration by 28% +/- 3% and by 21% +/- 4% (mean +/- SE; n = 7; p < 0.005), respectively.
   Clin Pharmacol Ther, 1996 · checked 2026-09-29
8. wcr-daily-r8-07 · agency fact sheet
   People taking warfarin and similar anticoagulants need to maintain a consistent intake of vitamin K from food and supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect [45].
   NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-09-29
9. wcr-daily-r8-08 · retrospective cohort
   Watercress was the infection mode in 98% of persons, with infections being attributed to four watercress species before 1980 versus only two species of Nasturtium sp. after 1981.
   Parasitol Res, 2000 · checked 2026-09-29
10. wcr-daily-r8-09 · case series
    Patient One was a 63-year-old male who developed a febrile illness 2 months after eating watercress in Marin County. Patient Two was a 38-year-old male who had eaten watercress with Patient One, and also developed a febrile illness. Both patients had eosinophilia and liver lesions on imaging.
    Am J Trop Med Hyg, 2013 · checked 2026-09-29
11. wcr-daily-r8-13 · registry search
    claims_search.py watercress: nothing in 21 CFR 101; euclaims_search.py watercress: nothing among 2330 claims, snapshot 2026-09-21
    EU Register on nutrition and health claims, snapshot 2026-09-21; 21 CFR part 101 · checked 2026-09-29
12. wcr-daily-r8-02 · crossover RCT
    Beneficial changes seen after watercress intervention were greater and more significant in smokers than in nonsmokers. Plasma lutein and beta-carotene increased significantly by 100% and 33% (P < 0.001), respectively, after watercress supplementation.
    Am J Clin Nutr, 2007 · checked 2026-09-29
13. wcr-daily-r8-05 · meta-analysis
    however, there is contention between reports, and the clinical significance of potential diet-drug interactions remains unclear. ... Cruciferous vegetables represented in the literature included broccoli, Brussels sprout, cabbage, cauliflower, radish, and watercress. ... The meta-analyses performed demonstrated a significant effect on CYP1A2 and glutathione S-transferase-alpha (GST-α), with consumption of Cruciferae increasing the activities of these enzymes by 20-40% and 15-35%, respectively.
    Clin Pharmacol Ther, 2020 · checked 2026-09-29