Lettuce is roughly 95% water and extremely low in calories, with a cup coming in at 10 to 15 calories depending on the variety. But that water-rich profile is deceptive. Lettuce delivers meaningful amounts of vitamin K, vitamin A, and folate, along with smaller contributions of potassium, calcium, and iron, plus a range of plant compounds with antioxidant properties.
Vitamins: Where Lettuce Really Stands Out
Vitamin K is the headline nutrient. A single cup of shredded romaine provides about 48 micrograms of vitamin K1, which is roughly 40% of the daily value. Butterhead lettuce edges slightly higher at 56 micrograms per cup. Your body uses vitamin K1 primarily for blood clotting and bone metabolism, so a couple of cups of lettuce at lunch gets you most of the way to your daily target.
Vitamin A is the other strength. Romaine is the standout here, delivering over 4,000 IU per cup, mostly in the form of beta-carotene, the orange pigment masked by chlorophyll in darker leaves. Per 100 grams, romaine provides more than 100% of the daily reference value for vitamin A. Iceberg still contributes a respectable 2,666 IU per cup, which surprises people who assume it’s nutritionally empty.
Folate varies dramatically by type. Romaine leads with 64 micrograms per cup (about 16% of the daily value), while red leaf lettuce trails at just 10 micrograms. If you’re eating lettuce partly for folate, romaine is worth choosing deliberately. Folate plays a central role in cell division and DNA synthesis, making it especially important during pregnancy.
Vitamin C is present but modest, ranging from 1 milligram per cup in red leaf to 3.3 milligrams in iceberg. You won’t meet your daily needs through lettuce alone, and vitamin C is also the nutrient most vulnerable to storage. Lettuce can lose 35 to 86% of its vitamin C within 10 days of refrigerated storage at standard fridge temperature, with lettuce showing the greatest percentage loss among common salad leaves.
Minerals in Lettuce
Lettuce won’t compete with beans or leafy greens like spinach for mineral content, but it does contribute useful amounts across several minerals, especially if you eat it daily. Butterhead lettuce is the mineral standout among common types, providing 131 milligrams of potassium, 19 milligrams of calcium, and 0.68 milligrams of iron per cup. Romaine follows closely with 116 milligrams of potassium and 16 milligrams of calcium.
Magnesium and phosphorus appear in small but consistent amounts across all varieties, typically 3 to 7 milligrams per cup for magnesium and 8 to 18 milligrams for phosphorus. Zinc is present in trace amounts. None of these numbers are large on their own, but lettuce is one of those foods people eat frequently and in volume, so the cumulative contribution to your mineral intake is real.
How Different Varieties Compare
Not all lettuce is created equal, and the differences are bigger than most people expect.
- Romaine is the best all-around choice for nutrient density. It leads in vitamin A, folate, and potassium, and ties for the top in vitamin K. It packs significantly more nutrition into a smaller serving weight (a cup is only 47 grams).
- Butterhead (butter lettuce) is the mineral leader, topping the list for calcium, iron, potassium, and vitamin K per cup. It’s a good pick if you prefer a softer texture and still want solid nutrition.
- Iceberg has the reputation of being nutritionally worthless, but that’s overstated. It delivers decent vitamin A (2,666 IU per cup), reasonable vitamin K (46 micrograms), and more vitamin C than romaine. Its main weakness is folate, where it lags far behind romaine.
- Red leaf actually scores lowest across most nutrients per cup, with the least potassium (52 mg), folate (10 micrograms), and vitamin K (39 micrograms) of the four common types. Its real advantage lies elsewhere: its pigments.
Phytonutrients and Antioxidants
Beyond standard vitamins and minerals, lettuce contains plant compounds that don’t show up on a nutrition label but matter for long-term health. The main carotenoid in lettuce is beta-carotene, making up 45 to 48% of total carotenoid content. Lutein accounts for 13 to 20%, and zeaxanthin for 11 to 15%. Both lutein and zeaxanthin concentrate in the retina of the eye and are associated with protection against age-related vision problems.
Red and darker-leaved lettuces bring additional compounds to the table. Researchers have identified ten different anthocyanins in red lettuce, including types derived from cyanidin and delphinidin, the same families of pigments found in blueberries and red cabbage. These are the compounds responsible for the reddish-purple coloring. Red lettuce also contains phenolic compounds like caffeoylquinic acid and the flavonoid rutin. These compounds have demonstrated antioxidant and anti-inflammatory activity in lab studies.
The color of lettuce leaves is a reasonable proxy for phytonutrient content. Darker outer leaves generally contain more carotenoids and phenolic compounds than pale inner leaves. If you’re tossing those darker outer leaves, you’re discarding the most nutrient-dense part of the head.
Naturally Occurring Nitrates
Lettuce is one of the higher-nitrate vegetables in the typical diet. The nitrate content can vary enormously depending on how the lettuce was grown, ranging from as low as 6 milligrams per 100 grams to over 1,000 milligrams per 100 grams based on nitrogen fertilizer levels. Dietary nitrates from vegetables convert to nitric oxide in the body, which helps relax blood vessels and supports healthy blood pressure. Interestingly, the fertilizer conditions that change nitrate levels don’t significantly alter the carotenoid or chlorophyll content, so two heads of lettuce can look identical but carry very different nitrate loads.
Keeping Nutrients Intact
Because lettuce is eaten raw, you avoid the cooking losses that affect many vegetables. But storage still matters. Vitamin C degrades rapidly after harvest, and lettuce loses more of it during refrigeration than most other salad greens. Folate is similarly sensitive to time and exposure to light and air.
To get the most from your lettuce, buy it as fresh as possible, store it in a sealed container or bag in the crisper drawer, and use it within a few days rather than letting it sit for a week or more. Whole heads retain nutrients better than pre-cut or bagged lettuce, since cutting exposes more surface area to oxidation. Washing right before eating rather than in advance also helps slow vitamin loss.