Watercress: Nutrients, What Research Shows and Safety

Watercress (Nasturtium officinale) is a peppery, leafy plant of the cabbage family (Brassicaceae) that grows in running water. The leaves and tender stems are eaten, usually raw in salads and sandwiches or in soups. People eat it for its vitamins and its sulfur-rich plant compounds. This page keeps the food, supplements and hype apart, and says plainly what the research does and does not show.

Read this first

• If you take warfarin, watercress is very high in vitamin K (USDA: 250 micrograms per 100 g). Doctors generally advise keeping vitamin K foods steady from week to week rather than avoiding them. Tell your clinic before big changes. [1][8]
• Wild watercress can carry a liver parasite (the liver fluke, Fasciola). CDC names watercress as an example of contaminated plants. [6][7] See the safety section.
• Allergy is possible with any food. For trouble breathing or swelling of the face or throat, call 911.
• Honest summary: watercress is a nutritious leafy green. Small, short trials of watercress products show changes in lab markers. None shows that it prevents or treats a disease.

What is in it (USDA values)

Source: USDA FoodData Central, "Watercress, raw" (SR Legacy, FDC 170068). [1] % Daily Value uses the FDA 2016 Daily Values; values vary with variety, ripeness and storage.

Watercress is rich in a glucosinolate called gluconasturtiin. When the leaf is chopped or chewed, an enzyme (myrosinase) turns it into phenethyl isothiocyanate (PEITC), which gives the peppery bite. Cooking inactivates the enzyme, although gut bacteria can supply some of it. [9] USDA also lists beta-carotene (1,914 mcg per 100 g) and lutein plus zeaxanthin, which are yellow-orange plant pigments (carotenoids). [1] The evidence on PEITC in people comes from small trials and lab studies, described below. [3][9]

What research says

The "most nutrient-dense food" ranking

You may read that watercress is the most nutritious food. This comes from a 2014 CDC paper that ranked watercress first (score 100) among 41 "powerhouse" fruits and vegetables. [2] The score averages the percent Daily Value of 17 nutrients per calorie, using USDA data for raw foods per 100 g. Watercress ranks high partly because it has very few calories. The authors state limits: scores were capped at 100, plant compounds such as glucosinolates were not scored, and the scheme still needs full validation. [2] The ranking is about nutrient density per calorie. It is not proof that eating watercress improves health, and a cup of watercress weighs only 34 g.

Eaten as food vs taken as a supplement or extract

The trials above mostly used concentrated products (capsules of dried watercress, a freeze-dried drink). One gave the equivalent of about 40 mg a day of PEITC. [3] That is not the same as a handful of leaves in a sandwich, and results from products do not automatically apply to the food. We did not find a source we read that compares the two.

How much is a normal serving

• The NHS counts 80 g of fresh, canned or frozen vegetables as one portion [10]. The USDA household portion for watercress is 1 cup chopped (34 g). [1] WHO advises at least 400 g of fruit and vegetables a day for people over 10 [11]. This is information, not a prescription.
• Cooking and nutrients: cooking inactivates the enzyme that makes PEITC; light steaming for under 5 minutes preserves some. [9] We did not find a source we read on cooking losses of vitamin C in watercress.

Safety, allergy and medicines

• Warfarin and vitamin K: vitamin K helps the liver make clotting proteins. MedlinePlus says people on warfarin may need to limit vitamin K foods, and above all should eat about the same amount daily, because sudden changes can alter the medicine's effect. [8] With 250 mcg per 100 g, watercress is a strong source. [1] Ask your clinic.
• Wild watercress and liver fluke: CDC says people are infected by eating plants, for example watercress, with the parasite's larvae (metacercariae) attached. [6] WHO says infection comes from eating aquatic vegetables with larvae attached; it needs no second intermediate host. [7] The sources we read do not give a safe way to treat wild plants at home, so we make no claim; if you gather wild watercress, ask a local health authority. Symptoms and treatment belong to a doctor; the CDC page we read refers to its parasite pages for treatment. [6]
• Allergy: Proper evidence not found in the sources we read on watercress allergy specifically.
• Kidney disease, thyroid, pregnancy: Proper evidence not found in the sources we read for watercress specifically. See cruciferous vegetables for the general thyroid discussion.
• Safety in trials: the 2025 review described the safety profile of watercress products as strong, but the trials were short. [4]

Choosing, storing and food safety

• Prefer watercress sold commercially over wild-picked plants, because the parasite risk described by CDC and WHO is linked to plants growing in contaminated fresh water. [6][7]
• The sources we read give no storage or washing advice specific to watercress: Proper evidence not found. General produce handling is covered in food storage and leftovers.

Related pages

• Cruciferous vegetables
• Sulforaphane and glucosinolates in cruciferous vegetables
• Leafy greens
• Foods and medicine interactions: vitamin K, grapefruit and others
• Superfoods: what the word means
• Dietary nitrate in beets and leafy greens