Arugula and spinach: nitrate moved blood pressure only in healthy people

The strongest evidence on this pair is about neither leaf by name. Pooled across 19 randomised trials, inorganic nitrate, the compound leafy greens are richest in, lowered systolic blood pressure by 2.42 mmHg in healthy adults (95% CI -4.28 to -0.57, P = 0.01) and by 0.82 mmHg in people with hypertension, which did not reach significance (95% CI -2.53 to 0.90, P = 0.35). Most of those trials used beetroot juice rather than a plate of greens, so the dose was cleaner than a salad delivers. The group with the most to gain from a lower reading showed nothing. We found no human study of arugula, or rocket, eaten as a food. The low-oxalate half of this comparison has never been tested in people, so everything else on this page is about spinach or about nitrate. Spinach is where the human measurements are, and the first one is unflattering. In 13 healthy adults, each eating a milk meal and a spinach meal carrying 200 mg of labelled calcium, 5.1 percent of the calcium in spinach was absorbed against 27.6 percent from milk, a gap of 22.5 percentage points inside the same person (P below 0.0001). Spinach does not work as a calcium source. This page has no safety section of its own: the cautions it does carry, on warfarin, on infants and nitrate, and on contamination of the raw leaf, sit under other headings.

How much is actually in it

• Spinach carried 736.6 mg of soluble oxalate per 100 g, yet only 1.93% of it reached the urine over 24 hours, and adding sour cream or milk lowered even that. — 10 volunteers eating 100 g of grilled spinach alone or with dairy, urine collected over 6 and 24 hours (n = 10) Evidence B source
  Soluble oxalate bioavailability 0.75 plus or minus 0.48% at 6 hours and 1.93 plus or minus 0.85% at 24 hours; dairy additions lowered it, P below 0.05
• People take in a median of about 108 mg of nitrate a day, which stays under the safe upper intake of 3.7 mg per kg of body weight. — adult populations in 55 observational studies, mostly assessed by food frequency questionnaire (n = 55 studies) Evidence C source
  Median daily nitrate intake 108 mg in healthy people and 110 mg in patients, against an upper intake of 3.7 mg nitrate ion per kg body weight
• Where crops were irrigated with untreated wastewater, spinach held a pooled mean of 2.86 mg of cadmium per kg, more than 9 times the EU limit of 0.2 to 0.3 mg per kg. — vegetable samples from 35 studies of wastewater-irrigated soils published 2000 to 2021 (n = 35 studies) Evidence C source
  Spinach pooled mean cadmium 2.86 mg/kg against an EU limit of 0.2 to 0.3 mg/kg; over 80% of vegetable samples above permissible limits; risk index above 1 for most crops

What your body absorbs

• Adults absorbed 5.1% of the calcium in spinach against 27.6% of the same amount of calcium from milk, a gap of 22.5 percentage points within the same person. — 13 healthy adults, each eating both a milk and a spinach test meal carrying 200 mg of labelled calcium (n = 13) Evidence B source
  Calcium absorption 5.1% from spinach against 27.6% from milk; within-subject difference 22.5 plus or minus 9.5 percentage points, P below 0.0001
• In people on warfarin, vitamin K began to shift the INR at 150 micrograms a day, and meals of spinach produced only a short-lived response that pointed to poor absorption from the leaf. — healthy volunteers stably anticoagulated for 13 weeks, given rising vitamin K1 doses and then vitamin K-rich meals Evidence C source
  Threshold dose lowering INR 150 micrograms a day, clinically relevant in 25% of participants; 100 micrograms a day did not interfere; spinach and broccoli meals gave a short-lived response

What cooking and storage change

• Among raw produce sampled in Ethiopian farms and markets, 54.2% of spinach carried parasites, second only to lettuce at 61.0%. — 6 659 vegetable and fruit samples in 29 studies from Ethiopia, 2010 to 2025 (n = 6659) Evidence C source
  Parasite contamination spinach 54.2%, lettuce 61.0%, cabbage 52.9%; overall contaminated produce 48.76%, 95% CI 40.78 to 56.74

What it does to your health

• Inorganic nitrate, the compound leafy greens are richest in, lowered systolic blood pressure by 2.42 mmHg in healthy people and did nothing in people with hypertension, pooled from 19 randomised trials. — healthy and hypertensive adults in 19 randomised controlled trials of inorganic nitrate (n = 19 trials) Evidence A source
  Healthy systolic -2.42 mmHg, 95% CI -4.28 to -0.57, P = 0.01; hypertensive systolic -0.82 mmHg, 95% CI -2.53 to 0.90, P = 0.35

Who this works differently for

• Home-prepared vegetable purees still cause nitrate poisoning in infants, while breastfed infants are not at risk even when the mother drinks water at 100 ppm nitrate nitrogen. — infants, American Academy of Pediatrics clinical report Evidence E source
  Risk sits with well water and home-prepared vegetable foods; commercially prepared infant foods carry little or no risk; breastfeeding infants not at risk at 100 ppm in maternal water

The bottom line

We have no USDA composition record for the paired name in this cohort. Oxalate is the reason the calcium stays put, and the oxalate itself mostly stays put too. Ten volunteers ate 100 g of grilled spinach that held 736.6 mg of soluble oxalate per 100 g, and 0.75 percent of it reached the urine over 6 hours and 1.93 percent over 24 hours, with sour cream or milk alongside lowering even that (P below 0.05). Ten people and one supplier of frozen spinach, so the composition figure travels less well than the principle, and grilling was chosen because it gives the oxalate no cooking water to leach into. That was a single meal in ten healthy volunteers, and no study on this page followed anyone who forms kidney stones, so a low urinary figure says nothing about stone risk. On nitrate as an intake, 55 observational studies put the median at about 108 mg a day, under the safe upper intake of 3.7 mg per kg of body weight, though most of those studies used food frequency questionnaires and food tables that disagree widely, because the nitrate in a given vegetable swings with season, light and fertiliser. Read that figure as an order of magnitude. The cautions here sit under other headings on this page rather than in a safety section, so they are worth collecting. On warfarin, healthy volunteers held stably anticoagulated for 13 weeks and given rising doses of vitamin K1 began to shift their INR at 150 micrograms a day, a change that mattered clinically in a quarter of them, while 100 micrograms a day did not interfere. Meals of spinach gave only a short-lived response, which the authors read as poor absorption from the leaf and as an argument for keeping greens steady rather than dropping them. Those were volunteers rather than patients managing their own diet, and the study was small and not randomised. For infants, the American Academy of Pediatrics said in a 2005 clinical report that home-prepared vegetable foods still cause nitrate poisoning, that commercial infant foods carry little or no risk, and that breastfed infants are not at risk even when the mother drinks water at 100 ppm nitrate nitrogen. That is a professional position rather than new data. Two findings are about where the leaf grew. In 35 studies of crops irrigated with untreated wastewater, spinach held a pooled mean of 2.86 mg of cadmium per kg, more than 9 times the EU limit of 0.2 to 0.3 mg per kg, and treated water brought levels back to control. In 6 659 produce samples from Ethiopian farms and markets, 54.2 percent of the spinach carried parasites, behind lettuce at 61.0 percent, in one country with its own irrigation and market practices. The percentage does not transfer to your shop. What transfers is that the hazard belongs to the raw leaf and cooking is the step that removes it.

Sources

1. arsp-r2-02 · randomised crossover trial
   Frozen commercially available spinach in New Zealand contains 736.6+/-20.4 mg/100g wet matter (WM) soluble oxalate and 220.1+/-96.5mg/100g WM insoluble oxalate. ... The mean bioavailability of soluble oxalate in the grilled spinach was 0.75+/-0.48% over a 6-hour period after intake and was 1.93+/-0.85% measured over a 24-hour period.
   Asia Pac J Clin Nutr, 2003 · checked 2026-09-24
2. arsp-r2-04 · systematic review of observational studies
   The median daily nitrate intakes in healthy and patient populations were 108 and 110 mg/d, respectively. ... The median estimated daily nitrate intakes by healthy and patient populations were similar, and these values were below the safe upper intake of daily intake (3.7 mg nitrate ion/kg body weight).
   Am J Clin Nutr, 2018 · checked 2026-09-24
3. arsp-r2-07 · meta-analysis of observational studies
   Certain species show extreme bioaccumulation, with Jew mallow (41.35 mg/kg), beet (23.19 mg/kg), and spinach (pooled mean 2.86 mg/kg) exceeding the EU safety limit (0.2-0.3 mg/kg) by factors of > 130, > 77, and > 9.5, respectively.
   Environ Monit Assess, 2026 · checked 2026-09-24
4. arsp-r2-01 · randomised crossover trial
   Absorption was higher from milk in every case, with the mean absorption from milk averaging 27.6% and from spinach, 5.1%.
   Am J Clin Nutr, 1988 · checked 2026-09-24
5. arsp-r2-05 · dose-response clinical trial
   The threshold K(1) dose causing a statistically significant lowering of the INR was 150 microg/day. ... The short-lived response after meals of spinach and broccoli suggested an inefficient bioavailability from these 2 sources.
   Blood, 2004 · checked 2026-09-24
6. arsp-r2-08 · meta-analysis of observational studies
   Lettuce (61.0%), salad (57.4%), spinach (54.2%), and cabbage (52.9%), were the vegetables most contaminated by parasites
   BMC Infect Dis, 2025 · checked 2026-09-24
7. arsp-r2-03 · meta-analysis of RCTs
   In the healthy population, inorganic nitrate lowered systolic blood pressure (-2.42 mmHg, 95% confidence intervals (CI) [-4.28, -0.57]; P = 0.01) but not diastolic blood pressure (-0.58 mmHg, 95% CI [-1.84, 0.68]; P = 0.36) ... However, in the hypertensive population, inorganic nitrates did not lower systolic blood pressure (-0.82 mmHg, 95% CI [-2.53, 0.90]; P = 0.35)
   Food Funct, 2023 · checked 2026-09-24
8. arsp-r2-06 · practice guideline
   However, reports of nitrate poisoning from home-prepared vegetable foods for infants continue to occur. Breastfeeding infants are not at risk of methemoglobinemia even when mothers ingest water with very high concentrations of nitrate nitrogen (100 ppm).
   Pediatrics, 2005 · checked 2026-09-24