Lettuce: two identical leaves, a hundred and seventy times the nitrate

A composition table tells you less about lettuce than about almost any other food. In one trial the researchers grew the same lettuce under two fertilization regimes and got two batches that looked, tasted and measured alike in color and volume. A 1.8 oz (50 g) portion of one held about 530 mg of nitrate. The same portion of the other held about 3 mg. That was growing conditions alone, in one experiment, so it shows how far the number can be pushed rather than how far it drifts in your shop. The high-nitrate portion lowered systolic blood pressure by about 4.9 mmHg between three and six hours after it was eaten, in 19 healthy adults aged 22 to 31, on one day. Nitrate taken as a supplement for a week or more did not significantly lower blood pressure across six trials and 181 people, though the confidence interval was wide enough to hide a useful drop. Leaf and supplement are not the same exposure, and neither of those studies followed anyone long enough to say what happens to a person. For scale, the acceptable daily intake for nitrate set by EU and JECFA experts is 3.7 mg per kg of body weight a day from all foods, about 222 mg for a 132 lb (60 kg) adult, so the 530 mg portion was about twice that. EU law caps nitrate in fresh lettuce at 3,000 to 5,000 mg per kg depending on season and growing method, which is 250 mg in 50 g at the highest cap. The high-nitrate portion was an experimental extreme above what may be sold.

The numbers, per 3.5 oz (100 g)

As people eat it, per 3.5 oz (100 g)

How much is actually in it

• EU law caps nitrate in fresh lettuce at 3,000 to 5,000 mg per kg depending on harvest season and whether it is grown under cover, and at 2,000 to 2,500 mg per kg in iceberg lettuce. — fresh lettuce placed on the EU market Evidence E source
  Nitrate maximum 3,000 to 5,000 mg/kg in fresh lettuce depending on season and cover, 2,000 to 2,500 mg/kg in iceberg type
• Two portions of lettuce grown to look identical held 530 mg and 3 mg of nitrate. — 19 healthy adults aged 22 to 31 who completed and complied, out of 24 recruited (n = 19) Evidence B source
  A 1.8 oz (50 g) portion of the high-nitrate material carried about 530 mg nitrate and 11 mg phenolic compounds, the low-nitrate material about 3 mg nitrate and 77 mg phenolics, from growing conditions alone

What a real portion looks like

• EFSA estimated that nitrate from all sources gives Europeans 0.97 to 4.15 mg per kg of body weight a day on average, and 1.59 to 8.73 mg at the 95th percentile. It noted that total nitrate exposure exceeded the 3.7 mg limit in all populations considered. Leafy vegetables and prepared salads were the main source in adults. — EU population groups from infants to the elderly, dietary surveys Evidence E source
  Nitrate from all sources: mean 0.97 (elderly) to 4.15 (toddlers) mg/kg bw per day, 95th percentile 1.59 to 8.73; ADI exceeded in all groups; leafy vegetables and prepared salads main contributors in children, adolescents, adults and the elderly
• A hundred grams of raw romaine with a high-fat meal cut the 0 to 4 hour glucose area under the curve from 385.7 to 361.9 in 16 healthy young men. — 16 healthy young men, mean age 22.8 years and mean BMI 23.7 (n = 16) Evidence B source
  0 to 4 hour glucose area under the curve was 361.9 with lettuce against 385.7 for control (P < 0.05) and against 382.3 for watercress (P < 0.01); peak insulin was 33.5 µIU/mL with lettuce against 43.8 for control (P < 0.05); triglycerides, total cholesterol, HDL, LDL, IL-6 and TNF-α did not differ

What your body absorbs

• Salad eaten with a fat-free dressing delivered essentially no carotenoids into the blood. — 7 adults (n = 7) Evidence B source
  After the fat-free dressing the appearance of alpha-carotene, beta-carotene and lycopene in chylomicrons was negligible; the reduced-fat dressing raised it above fat-free (P < 0.04) and the full-fat dressing raised it above reduced-fat (P < 0.02)

What cooking and storage change

• EFSA cites a study in which washing lowered the nitrate content of lettuce by 19% on average, against 26% for Chinese cabbage and 27% for spinach. — vegetable samples in a processing study reported by EFSA Evidence E source
  Washing lowered nitrate on average by 19% in lettuce, 26% in Chinese cabbage and 27% in spinach (fresh weight, p < 0.001)
• Lettuce that had been kept in a modified-atmosphere pack moved nothing in the blood at all. — 11 healthy volunteers, six men and five women (n = 11) Evidence C source
  After fresh lettuce, plasma total radical-trapping antioxidant potential rose by 1.3 mmol/l per 6 hours against 0.1 for the stored lettuce (P < 0.05), with quercetin, p-coumaric acid, caffeic acid, beta-carotene and vitamin C all rising from baseline; after stored lettuce none of the markers changed

What it does to your health

• High-nitrate lettuce lowered systolic pressure by about 5 mmHg in the three to six hours after it was eaten. — 19 healthy adults aged 22 to 31, mouthwash users and vegetarians excluded (n = 19) Evidence B source
  Systolic blood pressure fell 4.9 ± 4.2 mmHg between 3 and 6 hours after the high-nitrate portion compared with the low-nitrate one (P = 0.031), and the size of the fall tracked saliva nitrate concentration (P = 0.004); plasma nitrate rose 240% and salivary nitrate 910%
• Taking nitrate for a week or longer did not lower blood pressure in the pooled trials. — six trials, 181 adults, 59% male, mostly over 50 years old (n = 181) Evidence A source
  Mean difference against placebo was -3.81 mmHg systolic (95% CI -10.05 to 2.43), -2.00 mmHg diastolic (95% CI -4.37 to 0.38) and 0.34 bpm resting heart rate (95% CI -5.68 to 6.36), none statistically significant, with an average PEDro score of 8.16 indicating low risk of bias

Safety, limits and interactions

• The acceptable daily intake for nitrate set by the EU Scientific Committee on Food and by JECFA is 3.7 mg per kg of body weight per day, and it applies to nitrate from all food sources, vegetables included. — general population, EU and JECFA risk assessment Evidence E source
  Acceptable daily intake 0 to 3.7 mg nitrate ion per kg body weight per day, applicable to all dietary sources

What people believe that the data does not support

• Sanitizing washes cut bacteria on lettuce by less than a single log, and the interval reached zero. — 40 primary studies of laboratory-inoculated fresh produce (n = 40 studies) Evidence D source
  On lettuce sanitizer treatments achieved 0.68 mean log reductions with a confidence interval of 0.00 to 1.37, against 3.04 (2.32 to 3.76) on carrots; time and temperature both affected the result (P < 0.0001), and E. coli O157:H7 resisted ozone while Listeria and Salmonella resisted organic acids
• The only place lettuce appears in US food labeling law is as the example of a food whose selling point was never there to begin with. — US food labels Evidence E source
  A food may be called sodium free when it holds under 5 mg of sodium per reference amount, and where it meets that without any special processing the label must disclose that sodium is not usually present in the food, with leaf lettuce given as the worked example

Who this works differently for

• EFSA concluded in 2010 that nitrate levels in lettuce are not a health concern for children, with about 1% of lettuce samples above the legal maximum. It warned that badly stored cooked vegetables can turn nitrate into nitrite, and that children with gut infections are more sensitive. — infants and young children in the EU Evidence E source
  Nitrate in lettuce not a health concern for children; about 1% of lettuce samples above the maximum level; badly stored cooked vegetables can convert nitrate to nitrite; children with gut infections more sensitive
• In a crossover RCT in 12 healthy volunteers taking beetroot juice nitrate for 6 days, chlorhexidine mouthwash cut the rise in plasma nitrite by 200 nM versus a water rinse. Weaker mouthwash also blunted it. Resting blood pressure changes did not differ. — 12 healthy volunteers (n = 12) Evidence B source
  With chlorhexidine mouthwash the 2 h rise in plasma nitrite after beetroot juice was lower by 200 (SD 174) nM versus water rinse; resting BP change did not differ
• All 16 people in the lettuce meal trial were healthy young men with a normal BMI, so it says nothing about anyone else. — 16 healthy young men with normal BMI (n = 16) Evidence B source
  The authors state that restricting the trial to healthy young men with normal BMI limits generalization, and that people with obesity may be more prone to postprandial hyperglycemia and hyperlipidemia, so a larger effect might appear in them
• Across 27 studies about one vegetable sample in fourteen carried norovirus, and lettuce was the most sampled of them. — 27 studies of vegetable samples worldwide, most from Europe, with lettuce the most sampled commodity (n = 27 studies) Evidence C source
  Pooled prevalence 7% (95% CI 3 to 13); 18% (5 to 37) in samples taken at farms against 4% (1 to 8) at retail; 2% (0 to 8) for ready-to-eat vegetables against 9% (3 to 16) for non-ready-to-eat; genogroup GI was the most common at 3% (1 to 7)
• FDA says leafy greens have been repeatedly associated with illness from Shiga toxin-producing E. coli, most commonly O157:H7, while millions of servings are eaten safely every day. — US leafy greens supply Evidence E source
  FDA states that leafy greens have been repeatedly associated with illness from Shiga toxin-producing E. coli, most commonly O157:H7, while noting that millions of servings are consumed safely every day; the plan works on agricultural water, adjacent land use, soil amendments and harvest equipment

What is still unknown

• EFSA calculated that nitrate at the ADI, even with the highest oral conversion to nitrite of 9%, raises methaemoglobin measurably above the 1 to 3% background but not to a clinically significant level. — humans, EFSA calculation at the ADI dose Evidence E source
  At the ADI with the highest 9% nitrate-to-nitrite conversion, methaemoglobin rises measurably above background 1 to 3% but not to a clinically significant level

The bottom line

The salad dressing matters more than the leaf. Seven adults ate the same salad of spinach, romaine, tomato and carrot with dressings containing 0, 6 or 0.99 oz (28 g) of canola oil. After the fat-free dressing, essentially no carotenoids appeared in the blood. Not fewer, essentially none. Seven people and a mixed salad, so this cannot say what came out of the romaine specifically, and there is no trial of lettuce on its own. The direction is steep and easy to act on: put oil on it. A hundred grams of raw romaine alongside a burger and cheese flattened the glucose rise over the next four hours in 16 healthy young men, and lowered the insulin peak. The same weight of watercress did nothing, which argues against a general vegetable effect and leaves the cause unidentified. The trial authors add the part that most concerns readers: everyone in it was a healthy young man with a normal BMI, and people who get the biggest glucose rises after meals were never tested. Their guess that the effect would be larger in those people is a guess written in a discussion section. Storage takes something out that nobody can see. Eleven volunteers ate 8.8 oz (250 g) of fresh lettuce and their blood antioxidant capacity rose over six hours. Three days later they ate the same lettuce after cold storage under a modified atmosphere, the kind bagged salad travels in, and nothing in the blood changed. Eleven people, no randomized order, and a blood marker rather than anything a person feels, so read it as an upper bound on what the packed leaf is doing. Washing does less than people think. Pooling more than a thousand data points, commercial sanitizer treatments cut bacteria on lettuce by 0.68 log, with a confidence interval starting at zero, against 3.04 log on carrots. Leaf surfaces have stomata and cut edges where water cannot reach, and rinsing at home under a tap does less than a commercial wash rather than more. Across 27 studies about 7 percent of vegetable samples carried norovirus genetic material, 18 percent at the farm and 4 percent at retail, and detectable genome is not the same as an infection. That fall from 18 percent at the farm to 4 percent at retail fits what washing, sorting and chilling along the chain can take off, though the studies did not test that. So the sanitizer figure is the limit of what a wash can fix and not a reason to skip one. The US regulator runs a standing action plan for leafy greens and E. coli O157:H7 while stating that millions of servings are eaten safely every day. Both halves of that are true. On which note, the only mention of lettuce in American food labeling law is as the worked example of a claim that means nothing. A pack may say sodium free, and if the food got there without any processing it must also disclose that sodium is not usually present. The regulation names leaf lettuce. On nitrate itself, EFSA estimated in 2017 that Europeans get 0.97 to 4.15 mg per kg of body weight a day on average from all sources, and 1.59 to 8.73 mg at the 95th percentile. It noted that total intake exceeded the 3.7 mg limit in all populations it considered, with leafy vegetables and prepared salads the main source in adults, and said that judging whether this is a safety concern was outside the scope of that opinion. At the limit itself, EFSA calculated that methaemoglobin rises measurably above background but not to a clinically significant level. In one processing study, washing lowered nitrate in lettuce by 19% on average. For children, EFSA concluded in 2010 that nitrate in lettuce is not a health concern. It warned that badly stored cooked vegetables can turn nitrate into nitrite, and that children with gut infections are more sensitive to nitrate. The blood pressure effect runs through bacteria in the mouth. In 12 volunteers drinking beetroot juice, chlorhexidine mouthwash blunted the rise in plasma nitrite, though resting blood pressure did not differ between conditions. We found no card on nitrate in pregnancy, and no study of nitrate supplements or beetroot juice taken with blood pressure medicines.

Sources

1. hf2-let-5 · EU regulation
   6.1 Nitrates Maximum level (mg NO 3 /kg) ... 6.1.3 Fresh lettuce ( Lactuca sativa L.) except products listed in 6.1.4 6.1.3.1 Lettuce grown under cover, harvested between 1 October and 31 March 5 000 ... 6.1.3.4 Lettuce grown in the open air, harvested between 1 April and 30 September 3 000 6.1.4 ‘Iceberg’ type lettuce Including Grazer Krauthäuptl. 6.1.4.1 Lettuce grown under cover 2 500 ... 6.1.4.2 Lettuce grown in the open air 2 000
   Commission Regulation (EU) 2023/915 of 25 April 2023 on maximum levels for certain contaminants in food, Annex section 6.1 Nitrates · checked 2026-10-08
2. let-r5-01 · double-blind randomized controlled crossover trial
   Participants received a 50-g lettuce portion of HNLP (~ 530 mg NO3− and ~ 11 mg phenolic compounds per portion) or LNHP (~ 3 mg NO3− and ~ 77 mg phenolics) in the morning on two separate days.
   Eur J Nutr, 2022 · checked 2026-09-22
3. hf2-let-2 · EFSA scientific opinion
   From the exposure scenario considering the exposure to nitrates (expressed as nitrate ion) from all sources (food additives, natural presence and contamination), applying reduction factors for vegetables, mean exposure ranged from 0.97 mg/kg bw per day in the elderly to 4.15 mg/kg bw per day in toddlers. The 95th percentile of exposure to nitrates ranged from 1.59 mg/kg bw per day in the elderly to 8.73 mg/kg bw per day in children. ... whereas the leafy vegetables and prepared salads were the main contributors in children, adolescents, adults and the elderly. ... The Panel noted that total dietary exposure to nitrate from all sources exceeded the current ADI in all populations considered. Assessing whether or not the total dietary intake of nitrate was a safety concern was outside the scope of this re‐evaluation and beyond the remit of the ANS Panel.
   EFSA ANS Panel, Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives, EFSA Journal 2017;15(6):4787 · checked 2026-10-08
4. let-r5-04 · randomized controlled crossover trial
   In this study on healthy men, the addition of lettuce to a moderately high-fat meal delayed the postprandial glycemic response.
   Lipids Health Dis, 2021 · checked 2026-09-22
5. let-r5-06 · randomized controlled crossover trial
   Essentially no absorption of carotenoids was observed when salads with fat-free salad dressing were consumed.
   Am J Clin Nutr, 2004 · checked 2026-09-22
6. hf2-let-4 · EFSA scientific opinion
   The report identified a statistically significant (p < 0.001) average reduction, based on fresh weight, for washing lettuce (−19%), Chinese cabbage (–26%) and spinach (−27%).
   EFSA ANS Panel, Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives, EFSA Journal 2017;15(6):4787 · checked 2026-10-08
7. let-r5-07 · controlled comparative feeding study
   Our present results showed that ingestion of MAP-stored lettuce does not modify plasma redox status in healthy subjects.
   Br J Nutr, 2002 · checked 2026-09-22
8. let-r5-02 · double-blind randomized controlled crossover trial
   Systolic BP was reduced 4.9 ± 4.2 mmHg (P = 0.031) between 3 and 6 h after ingestion of HNLP compared with LNHP
   Eur J Nutr, 2022 · checked 2026-09-22
9. let-r5-03 · systematic review and meta-analysis of randomized controlled trials
   Compared to the placebo condition, NO₃⁻ supplementation did not result in significant reductions in DBP (MD: -2.00 mm Hg; 95% CI: -4.37 to 0.38 mm Hg); SBP (MD: -3.81 mm Hg; 95% CI: -10.05 to 2.43 mm Hg); and RHR (MD: 0.34 bpm; 95% CI: -5.68 to 6.36 bpm).
   Nutr Res, 2026 · checked 2026-09-22
10. hf2-let-1 · EFSA scientific opinion
    The current acceptable daily intakes (ADIs) for nitrate of 3.7 mg/kg body weight (bw) per day were established by the SCF (1997) and JECFA (2002). ... The SCF retained thus an ADI of 0–3.7 mg/kg bw per day for nitrate ion (equivalent to 0–5 mg/kg bw per day for sodium nitrate) and confirmed that this ADI was applicable to all sources of dietary exposure to nitrates (SCF, 1997 ).
    EFSA ANS Panel, Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives, EFSA Journal 2017;15(6):4787 · checked 2026-10-08
11. let-r5-08 · meta-analysis of laboratory studies
    In general, sanitizer treatments led to lower mean log reductions when applied to leafy greens (for example, 0.68 log reductions [0.00 to 1.37] achieved in lettuce) compared to other, nonleafy vegetables (for example, 3.04 mean log reductions [2.32 to 3.76] obtained for carrots).
    Appl Environ Microbiol, 2015 · checked 2026-09-22
12. let-r5-11 · codified federal regulation
    (iii) As required in § 101.13(e)(2) if the food meets these conditions without the benefit of special processing, alteration, formulation, or reformulation to lower the sodium content, it is labeled to disclose that sodium is not usually present in the food (e.g., “leaf lettuce, a sodium free food”).
    21 CFR 101.61, Nutrient content claims for the sodium content of foods · checked 2026-09-22
13. hf2-let-6 · EFSA scientific statement
    For children, the CONTAM Panel concluded that levels of nitrate in lettuce are not a health concern. ... because only about 1 % of lettuce samples and 5 % of spinach samples exceeded the respective current maximum levels. Inappropriate storage of cooked vegetables can result in in situ conversion of nitrate to nitrite, resulting in an increased potential for causing methaemoglobinaemia. The CONTAM Panel noted that infants and children with bacterial infections of the gastrointestinal tract are more sensitive to nitrate, and recommended against feeding spinach to such children.
    EFSA CONTAM Panel, Statement on possible public health risks for infants and young children from the presence of nitrates in leafy vegetables, EFSA Journal 2010;8(12):1935 · checked 2026-10-08
14. hf2-let-7 · randomized controlled trial
    12 healthy volunteers mouth-rinsed with STRONG, non-chlorhexidine mouthwash (WEAK) and deionised water (CON) 3 times a day, and ingested 70 mL BR (6.2 mmol NO3-), twice a day, for 6 days. ... In addition, the rise in plasma [NO2-] at 2 h was lower in STRONG compared with WEAK (by 89±112 nM) and CON (by 200±174 nM) and in WEAK compared with CON (all P<0.05). Changes in resting BP were not different between conditions (P>0.05).
    Int J Sports Med, 2015 · checked 2026-10-08
15. let-r5-05 · stated limitation within a randomized controlled crossover trial
    the study was performed only on healthy young men with normal BMI, which limits the generalization of our findings
    Lipids Health Dis, 2021 · checked 2026-09-22
16. let-r5-09 · systematic review and meta-analysis of prevalence studies
    This analysis showed that the pooled HuNoVs prevalence in vegetables was 7 % (95 % confidence interval (CI): 3-13) worldwide.
    Int J Food Microbiol, 2024 · checked 2026-09-22
17. let-r5-10 · regulatory action plan
    However, while millions of servings are consumed safely every day, leafy greens have been repeatedly associated with illnesses caused by Shiga toxin-producing E. coli (STEC), the most common of which is E. coli O157:H7.
    FDA, Leafy Greens STEC Action Plan · checked 2026-09-22
18. hf2-let-3 · EFSA scientific opinion
    In view of the large variability observed among the populations on the proportion of nitrite that can be formed from nitrate in the mouth, the Panel considered that even using the highest nitrate‐to‐nitrite conversion factor of 9% a dose corresponding to the ADI of 3.7 mg/kg bw per day will be converted into 0.25 mg nitrite ion/kg bw per day. With this dose, the methaemoglobin levels will increase above background levels (1–3%) which is measurable, but not clinically significant.
    EFSA ANS Panel, Re-evaluation of sodium nitrate (E 251) and potassium nitrate (E 252) as food additives, EFSA Journal 2017;15(6):4787 · checked 2026-10-08