Watercress

Overview

Watercress (Nasturtium officinale) is an aquatic flowering plant in the mustard family (Brassicaceae), native to Europe and Asia, that grows along the banks of slow-moving streams and rivers. It has been consumed since ancient times — Roman soldiers ate it for vitality, and Hippocrates reportedly established the first hospital near a stream to ensure a supply of fresh watercress for patients. In 2014, the Centers for Disease Control and Prevention (CDC) published a nutrient density scoring system for vegetables and fruits, and watercress received a perfect score of 100 — ranking it the single most nutrient-dense vegetable among the 41 "powerhouse" foods evaluated. Despite this distinction, watercress remains underused in many Western kitchens, while it is a staple ingredient in Chinese soups and British cream teas.

Nutritional Highlights

• Glucosinolates (especially PEITC): Watercress is exceptionally rich in gluconasturtiin, which is broken down to phenethyl isothiocyanate (PEITC) when the leaves are chewed or chopped. PEITC is one of the most studied dietary compounds for cancer chemoprevention, with robust evidence for inhibiting tumour initiation and progression.
• Vitamin K: Watercress delivers approximately 250 mcg of vitamin K1 per 100 g — more than twice the adult daily adequate intake — supporting blood clotting and bone mineralisation.
• Vitamin C: Providing about 43 mg of vitamin C per 100 g, watercress covers roughly 50% of the adult daily requirement and supports collagen production, immune function, and antioxidant defence.
• Beta-carotene (provitamin A): Watercress provides 1.5 mg of beta-carotene per 100 g, which the body converts to vitamin A for eye health, immune function, and cell differentiation.
• Calcium: With approximately 120 mg of calcium per 100 g — comparable to cow's milk on a per-calorie basis — watercress is a useful plant source of this bone-building mineral.
• Iodine: Watercress is one of the few land plants that concentrates iodine from the water in which it grows, contributing to thyroid hormone synthesis when consumed regularly.

Health Benefits

The cancer-preventive potential of watercress's glucosinolates has been studied extensively, particularly in relation to PEITC. A seminal randomised crossover trial published in the American Journal of Clinical Nutrition (2007) found that consuming 80 g of watercress daily for eight weeks significantly reduced DNA damage in white blood cells (measured by the comet assay), reduced plasma levels of the cancer-promoting oxidised form of LDL, and increased antioxidant capacity. PEITC has since been shown in multiple cell and animal studies to inhibit phase I enzymes that activate carcinogens and to induce phase II enzymes that neutralise them — a dual mechanism that makes it particularly effective in cancer chemoprevention research.

Watercress is particularly well-studied in relation to breast cancer. A 2010 randomised crossover trial found that breast cancer survivors who consumed a bag of watercress daily had measurably elevated plasma PEITC levels and significantly altered expression of proteins involved in tumour suppression and apoptosis, including HIF-1 alpha — a protein implicated in cancer cell survival under hypoxic conditions. While clinical translation is still ongoing, the mechanistic evidence for PEITC's anti-cancer activity is among the strongest of any dietary compound.

Bone health is a secondary benefit supported by watercress's nutritional profile. Its combination of vitamin K1 (which activates osteocalcin, a protein that anchors calcium into bone matrix), calcium, and beta-carotene makes it an unusually complete bone-protective food. The EPIC cohort study found that dietary vitamin K intake — predominantly from leafy green vegetables — was significantly associated with lower hip fracture risk in older adults.

For cardiovascular health, watercress provides dietary nitrates (converted to vasodilatory nitric oxide), lutein (protective against atherosclerosis), and vitamin C (which improves endothelial function and reduces LDL oxidation). These combined mechanisms position watercress as a high-impact cardiovascular-protective food relative to its calorie content of only 11 kcal per 100 g.

How to Use

• Eat raw for maximum glucosinolate activity: The enzyme myrosinase that converts glucosinolates to PEITC is deactivated by heat. For cancer-preventive benefit, consume watercress raw or add to dishes only at the very end of cooking, after removing from heat, so the enzyme can act when the leaves are chewed.
• Use in salads and sandwiches: Watercress's peppery bite pairs well with mild, creamy ingredients. Classic combinations include watercress with pear and Stilton cheese, or in egg mayonnaise sandwiches in the British tradition. Add to any green salad for a nutrient density boost.
• Traditional Chinese soups: In Cantonese cooking, watercress is simmered in pork or chicken broth with dates and dried figs for a nourishing soup (西洋菜湯, xī yáng cài tāng). While prolonged cooking deactivates myrosinase, the vitamin K, calcium, and carotenoids remain available.
• Blend into green smoothies and juices: A handful of watercress blended into a green smoothie with apple, cucumber, and lemon juice adds glucosinolates, vitamin C, and vitamin K without overwhelming the flavour. Its peppery taste is tempered significantly when blended with sweet fruit.
• Select and store carefully: Choose bright green, unwilted watercress with no yellowing. Watercress is highly perishable — wrap in a damp paper towel and store in a sealed bag in the refrigerator, using within two days. Alternatively, stand the stems in a glass of water in the refrigerator to extend freshness by a further day or two.