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Lettuce
Kopfsalat · (Lactuca sativa var. capitata)
Daisy family (Asteraceae)
Description
Butterhead lettuce forms firm, round heads of tightly overlapping leaves, harvested whole from May to October, and belongs botanically to the daisy family. At 95–97 percent water it is low in calories yet supplies notable amounts of vitamin K1 (around 102 µg/100 g), beta-carotene, folate and potassium – clinical studies link regular consumption with benefits for digestion and immunity, and folk tradition also credits it with a mildly calming effect. The milky sap of bolting plants contains lactucin and lactucopicrin, though at customary salad amounts the concentration stays safely low. Because it is eaten raw, thorough washing matters to avoid bacterial and viral pathogens. In pregnancy it is considered a particularly valuable source of folate; people on vitamin K antagonists should keep their daily intake consistent rather than avoiding it.
Lettuce is the world's most widely consumed raw vegetable. 100 g supplies approx. 102 µg vitamin K (about 85 % DV), 73 µg folate, 166 µg RAE vitamin A (from beta-carotene), 238 mg potassium and only 13 kcal — making it an ideal satiety vegetable with low energy density. The tender, water-rich leaves (95.5 % water) provide dietary fibre, support intestinal peristalsis and promote hydration. Consumed raw in salads, sandwiches, wraps or briefly braised — classic early-summer vegetable, often the first outdoor crop harvested in German-speaking regions.
Lettuce and other Lactuca varieties with dark green leaves are significant sources of beta-carotene (provitamin A). 100 g of butterhead lettuce supplies approx. 166 µg RAE vitamin A — comparable to butterhead types (Boston, Bibb). Beta-carotene is an antioxidant compound and precursor of vitamin A, essential for visual function, immune defence and skin integrity. Dark green outer leaves contain 4–8× more beta-carotene than pale inner leaves — these should be eaten rather than discarded.
Lettuce contains small amounts of the sesquiterpene lactones lactucin and lactucopicrin in its milky sap — the same bitter compounds concentrated in the related wild lettuce (Lactuca virosa) as lactucarium. In European folk medicine of the 17th–19th centuries, eating a head lettuce before bedtime was regarded as a sleep-promoting home remedy. Animal studies confirm sedative and analgesic effects of lactucin and lactucopicrin; at normal salad consumption levels, concentrations are too low for a pharmacological effect.
In traditional phytotherapy (PFAF, Grieve), Lactuca species are described as mildly diuretic, slightly antispasmodic and calming (nervine). The milky sap (lactucarium) from flowering plants was sold in pharmacies in the 19th century as a cough remedy and mild sedative. Cultivated lettuce has very low lactucarium content compared to Lactuca virosa; the recorded uses refer primarily to wild species and flowering plants.
Lettuce is a relevant vitamin K source: 100 g of butterhead types supplies approx. 102 µg vitamin K1 — about 85 % of the daily requirement. Vitamin K is essential for blood coagulation (factors II, VII, IX, X) and bone mineralisation (osteocalcin activation). Dark-green lettuce varieties (unlike iceberg lettuce) supply significantly more vitamin K. Patients on anticoagulant therapy should keep their daily vitamin K intake consistently stable.
The flowering or bolting of lettuce is evaluated positively in folk medicine: in Central European folk belief, the milky sap of the bolting plant was considered especially valuable (bitter, concentrated). In everyday cooking, bolting plants are however usually discarded. Horticulturally important: harvest lettuce before bolting in cool weather with even watering, as bitterness and toughness of leaves increase.
Lettuce seeds can be sprouted and eaten as sprouts — they are rich in proteins and contain germination-active enzymes. In the traditional cooking of the Middle East and Central Asia, lettuce seeds are occasionally pressed for oil (lettuce oil). The oil is edible, but not economically significant due to small seed size (PFAF). Consume seed sprouts 3–5 days after sprouting at room temperature, then refrigerate.
LACTUCARIUM: The milky sap in bolting lettuce contains lactucin and lactucopicrin. At normal salad quantities, concentrations are safely low. Very large amounts of bolting lettuce or isolated milky sap can, according to PFAF, cause drowsiness, paradoxical over-excitation and in extreme doses cardiac paralysis — no risk at customary consumption. CONTAMINATION RISK: Lettuce is eaten raw and can harbour bacterial and viral pathogens (E. coli, Salmonella, Norovirus); wash leaves thoroughly before consumption and consider source. ANTICOAGULANTS: Lettuce is vitamin K-rich; patients on coumarin therapy should eat consistently stable daily amounts.
Lettuce is very suitable in pregnancy — a valuable source of folate and vitamin A. Pay attention to thorough washing of leaves and source hygiene (raw-milk cheese analogy: Listeria risk with contaminated lettuce). Normal consumption without restriction.
Safe during lactation. In very old traditions lettuce was considered galactagogue (milk-promoting) — not scientifically substantiated.
Lettuce is suitable from weaning age — tender, easily pureeable leaves as solid food from approx. 8–10 months. Cut finely for toddlers; whole leaves only once reliable chewing is established. Hygiene: wash leaves thoroughly.
Drug interactions
Antikoagulanzien (Vitamin-K-Antagonisten, z. B. Warfarin, Phenprocoumon)
Butterhead lettuce contains approx. 102 µg vitamin K1 per 100 g. Sudden changes in daily lettuce amounts can destabilise the INR value. Patients should keep total daily vitamin K intake from green vegetables consistently stable, not avoid them.
Contraindications
- No known absolute contraindications at customary food consumption. Known hypersensitivity to Asteraceae (daisy family) — rare but possible.
Harvested part: whole heads
- Time of day:
- Harvest in the morning or on cool evenings — lettuce heads wilt at midday and often do not recover fully. Maturity signs: head is firm and dense, leaves close up. Just before bolting (elongation of the central axis) lettuce is at its flavour optimum.
- Drying:
- HARVEST AND STORAGE: Cut entire head with a sharp knife just above soil level. Remove outer soiled leaves, but do not wash (store unwashed). In the vegetable drawer of the refrigerator (0–2 °C, high humidity 95–98 %) in a perforated plastic bag or vegetable container: keeps 8–12 days. Pressure-sensitive — do not stack. Do not store near apples or other ethylene-producing fruits (ethylene accelerates wilting and brown spotting). Freshly harvested and immediately processed gives the highest nutrient and flavour content.
- Storage:
- 0.4 months — 0–2 °C, high humidity (95–98 %), unwashed, pressure-protected packaging. Separate from ethylene producers (apples, tomatoes).
- Time of day:
- Single leaf harvest (cut-and-come-again): detach or cut outer leaves one by one from outside inward once fully grown. The head continues growing from inside. This method considerably extends the harvest period and is ideal for balcony and raised bed cultivation.
- Drying:
- SINGLE LEAF HARVEST: Individual leaves can be used within 1–2 days of harvest; not shelf-stable without refrigeration. In the refrigerator wrapped moist, 2–3 days. Do not dry — lettuce leaves do not dry sensibly.
- Storage:
- 0.07 months
- LactucinSesquiterpeneContent: Spuren in Lactuca sativa; höher in L. virosa (bis 1 % TG)Leaf
Bitter sesquiterpene lactone from the guaianolide group. Main constituent of the lactucarium milky sap; present only in trace amounts in cultivated lettuce, concentrates during bolting. Animal studies demonstrate sedative and analgesic properties; clinical evidence in humans is lacking.
- LactucopicrinSesquiterpeneContent: Spuren in Lactuca sativa; in L. virosa höher konzentriertLeaf
Bitter sesquiterpene lactone (also called intybin) responsible for the intensely bitter taste of bolting lettuce. Lactucopicrin acts as an acetylcholinesterase inhibitor, shows sedative and analgesic properties in animal studies and antimalarial activity in vitro. At dietary consumption levels, no pharmacologically relevant effect is expected.
- Vitamin K1 (Phylloquinon)VitaminContent: ca. 102 µg/100 g frisch (Butterhead)Leaf
Butterhead lettuce is a significant vitamin K source — about 85 % of the daily requirement per 100 g. Dark green outer leaves are considerably richer than pale inner leaves. Vitamin K is essential for blood coagulation and bone metabolism.
- Beta-Carotin (Provitamin A)OtherContent: ca. 1100-2500 µg/100 g frisch (sortenabhängig)Leaf
Most important fat-soluble antioxidant in lettuce. Beta-carotene is converted in the body as needed to vitamin A (retinol). Dark green varieties (e.g. romaine, batavia) contain 4–8× more beta-carotene than pale iceberg types. Beta-carotene absorption is considerably improved by added fat (oil dressing).
- Folsäure (Folat, Vitamin B9)VitaminContent: ca. 73 µg/100 g frisch (Butterhead)Leaf
Butterhead lettuce is a good folate source — 73 µg/100 g ≈ 18 % DV. Folate is essential for cell division and amino acid metabolism; particularly important in early pregnancy (neural tube prevention). Iceberg lettuce contains significantly less folate (approx. 3–5× less than butterhead types).
- KaliumMineralContent: 238-260 mg/100 g frischLeaf
Lettuce is a moderate potassium source. Potassium is essential for neuromuscular function and blood pressure regulation. For individuals with potassium restriction (severe renal failure), even lettuce should be considered — but at a very low level compared to e.g. potatoes.
- Wasser (Zellwasser mit gelösten Mineralstoffen)OtherContent: 95-97 %Leaf
The exceptionally high water content (95.5 %) makes lettuce a natural hydration vegetable with low energy density. The cell water contains osmotically active mineral salts (potassium, calcium, magnesium) and is a key factor behind the cooling and mildly diuretic effect known in folk medicine.
- [1]MonographUSDA FoodData Central — Lettuce, butterhead (includes boston and bibb types), raw(accessed: 2026-05-22)
- [4]MonographLettuce, raw, butterhead — nutritional value per 100g (nutritionvalue.org, citing USDA SR)(accessed: 2026-05-22)
- [5]MonographPlants For A Future (PFAF) — Lactuca sativa database entry(accessed: 2026-05-22)
- [2]WikipediaLettuce (Wikipedia EN)(accessed: 2026-05-22)
- [3]WikipediaKopfsalat (Wikipedia DE)(accessed: 2026-05-22)
- [6]WikipediaLactucarium (Wikipedia EN)(accessed: 2026-05-22)
- [7]WikipediaLactucopicrin (Wikipedia EN)(accessed: 2026-05-22)
🤝 Permaculture Partners
In your garden, this plant acts as:
✨ Best symbiotic partners
- 🌿 Onion Classic companion-planting partner.
- 🌿 Chives Chives distract aphids and keep lettuce pests away.
- 🌿 Beetroot Classic companion-planting partner.
- 🌿 Cabbage Classic companion-planting partner.
- 🌿 Broccoli Classic companion-planting partner.
- 🌿 Cucumber Classic companion-planting partner.
- 🌿 Carrot Classic companion-planting partner.
- 🌿 Eruca sativa Classic companion-planting partner.
- 🌿 Fragaria vesca Lettuce as ground cover between strawberry rows.
- 🌿 Parsnip Classic companion-planting partner.
- 🌿 Pea Classic companion-planting partner.
- 🌿 Black Spanish radish Classic companion-planting partner.
- 🌿 Radish Classic: radishes fast, lettuce slow — perfect row companions.
- 🌿 Rhubarb Lettuce as ground cover beneath the large rhubarb leaves.
- 🌿 Spinach Classic companion-planting partner.
⚠️ Better not planted together
📦 Part of these planting sets:
Source: Gertrud Franck, Gesunder Garten durch Mischkultur (1980, eigene Kuration) | Helga und Margarete Langerhorst, Mein gesunder Naturgarten (eigene Kuration)