Lettuce benefits: the evidence that it makes you sleepy is not about the leaves on your plate

Key benefits

1. 01Early research

   The sleep trials are real — but they used extract capsules and seeds

   Randomised trials in people on lettuce and sleep do exist. This site identified two.

   First, 2025, Nutrients. A randomised, double-blind, placebo-controlled trial.

   • Participants: Korean adults aged 30–65 with PSQI > 5 (poor sleep quality)
   • Intervention: two capsules daily for four weeks
   • Measures: PSQI, actigraphy and polysomnography
   • Analysis: ANCOVA adjusted for baseline, age and sex

   Measure	Test	Placebo	p
   PSQI global	6.48	7.41	0.046
   Total sleep time (actigraphy)	421.7 min	386.6 min	0.0023
   Sleep efficiency (actigraphy)	83.9%	81.0%	0.034
   Total sleep time (polysomnography)	358.9 min	322.1 min	0.046
   Sleep efficiency (polysomnography)	86.9%	79.6%	0.018
   Wake after sleep onset	39.3 min	68.2 min	0.0042

   That polysomnography was used is a strength. These are instrument measurements, not only a questionnaire.

   Second, 2018, Journal of Ethnopharmacology. A double-blind randomised placebo-controlled trial of lettuce seeds for pregnancy-related insomnia. A 2022 pilot also tested lettuce seed syrup for insomnia in patients with breast cancer.

   Several distinctions have to be kept.

   First, the form differs. These trials used extract capsules and seeds — not the leaves eaten in a wrap. An extract concentrates particular compounds; seeds are a different part of the plant.

   Second, the cultivar was specified. The 2025 trial used an extract of Heukharang, a particular cultivar, and its conclusion names that extract. Nothing in the trial shows the green or red leaf lettuce from a supermarket behaves the same.

   Third, it cannot be converted into leaves. The paper does not say how many lettuce leaves two capsules correspond to, and this site does not invent numbers that do not exist.

   Fourth, look at the size. The PSQI difference is 0.93 points. PSQI runs 0–21, and above 5 counts as poor sleep quality. The test group's final score of 6.48 is still above 5. Sleep improved; it did not cross back over the threshold.

   Fifth, the funding came from a food company. This is stated in the paper, along with a declaration that the funder was not involved in design or analysis. That does not invalidate the result, but it is information to hold while reading it.

   So is "lettuce makes you sleepy" baseless?

   Lettuce's milky sap (lactucarium) is known to contain lactucin and lactucopicrin, the source of its bitterness, and their sedative activity has been studied.

   But those compounds concentrate in the stem and sap rather than the leaf, and increase as the plant bolts. The young leaves we eat carry relatively little.

   The honest conclusion: there are randomised trials in which a lettuce extract improved sleep. There is no evidence that ten leaves in a wrap do the same. If you felt sleepy after a dinner with lettuce, a full meal is the more likely explanation.

   [1][2]
2. 02Nutrition data

   15 kcal and 370 µg of vitamin A per 100 g — but a leaf is 5–10 g

   Per 100 g of raw green leaf lettuce:

   • 15 kcal, protein 1.36 g, fat 0.15 g
   • Of 2.87 g of carbohydrate, 1.3 g is fibre, sugar 0.78 g
   • Vitamin A 370 µg RAE — 41% of the requirement
   • Beta-carotene 4,440 µg
   • Folate 38 µg, vitamin C 9.2 mg
   • Potassium 194 mg, calcium 36 mg, iron 0.86 mg
   • Sodium 28 mg

   The 15 kcal defines it. Over 95% water. However much lettuce you eat, the calories barely move.

   The 370 µg of vitamin A is the surprise, coming from 4,440 µg of beta-carotene. The darker the leaf the more there is — which is why the dark outer leaves are worth more than the pale inner ones.

   But a leaf is 5–10 g. Converted to what you actually eat:

   	100 g	One leaf (8 g)	Ten leaves (80 g)
   Energy	15 kcal	1.2 kcal	12 kcal
   Vitamin A	370 µg	30 µg	296 µg (33%)
   Folate	38 µg	3 µg	30 µg
   Fibre	1.3 g	0.1 g	1.0 g
   Potassium	194 mg	16 mg	155 mg

   Ten leaves is 12 kcal, and brings a third of the vitamin A requirement. For the calories, that is an excellent trade.

   The fibre is only 1.0 g, though. Eating a lot of lettuce does not fill the fibre gap.

   Beta-carotene is fat-soluble, so eating it with grilled pork is not a bad pairing for absorption — though that meat's fat and sodium have to be counted separately.

   Varieties differ.

   • Green and red leaf lettuce — the table above. Darker leaves, more beta-carotene
   • Iceberg — more water and far less vitamin A
   • Romaine — between the two

   "Lettuce" covers varieties whose nutrition is not comparable.

   Washing. Rinse leaf by leaf under running water and shake it completely dry. Wet leaves make the dipping sauce slide off and go soft in storage.

   Storage. Dried, wrapped in kitchen paper in a sealed box in the fridge, it keeps three or four days. A browned cut stem is polyphenol oxidase, not spoilage.

3. 03Not established

   "Don't eat lettuce the night before an exam" — the evidence makes that an overreaction

   This entry sorts through a common worry.

   Students are told to avoid lettuce before a test, on the grounds that it makes you drowsy. Read against the trials above, that worry is overdone.

   First, what showed an effect was an extract — two capsules a day for four weeks. That is not the same as a few leaves at one meal.

   Second, even that effect is not "knocked out". Total sleep time rose by 35 minutes and PSQI improved by 0.93 points. It is not a finding about reduced daytime alertness.

   Third, the participants already had poor sleep. Nothing in the trial shows the same result in someone who sleeps well.

   So why the drowsiness? More plausible explanations exist.

   • Postprandial somnolence — a large meal makes you sleepy, more so with more carbohydrate
   • The fullness after a heavy meat dinner
   • Alcohol — the meals where Korean lettuce wraps appear usually include it

   There is no basis for singling out the lettuce.

   Equally, expecting lettuce to work as a sleeping aid goes past the evidence. Persistent insomnia is a reason to see a doctor. Sleep apnoea, anxiety and depression, caffeine and alcohol, shift work — none of these is solved with food.

   One last point. That a trial of lettuce seeds targeted pregnancy-related insomnia is not a reason to use lettuce seed products during pregnancy on your own. Seeds and extracts are not the leaf, and any use in pregnancy needs a doctor's input.

How to eat it well

What to watch out for