Greens and spinach: rich on paper, thinner in a 25 g cup

The one meta-analysis at the top of the evidence here is a deflation. Across 118 randomized trials, nitrate rich foods gave a trivial benefit to endurance performance (SMD 0.15, p < 0.001), that benefit came from beetroot, red spinach and Swiss chard showed none, and no effect on performance was found in women, which the authors of that synthesis say may be physiology or too few participants. Raw mature spinach is genuinely dense on paper. The UK table gives it 394 micrograms of vitamin K1, 170 mg of calcium, 2.1 mg of iron and 114 micrograms of folate per 3.5 oz (100 g). A cup of raw spinach weighs 0.88 oz (25 g) in the USDA survey table and the guideline amount for a salad is 50 g, so an ordinary serving is a quarter or a half of those per 3.5 oz (100 g) figures. What reaches you is a further step down: the NIH puts uptake of phylloquinone from spinach at 4 to 17 percent of what the same vitamin gives from a tablet. The leaves also differ from each other. Calcium in baby spinach ran from 48.2 to 92.1 mg per 3.5 oz (100 g) across eight USDA samples, a spread of 64 percent around the mean, and USDA publishes no such range for mature spinach.

How much is actually in it

• Raw mature spinach carries 394 micrograms of vitamin K1, 170 mg of calcium, 2.1 mg of iron and 114 micrograms of folate per 3.5 oz (100 g). — UK food composition dataset, raw mature spinach, per 3.5 oz (100 g) Evidence E source
  Vitamin K1 394 ug, calcium 170 mg, iron 2.10 mg, folate 114 ug, vitamin C 26 mg, magnesium 54 mg per 3.5 oz (100 g)
• Calcium in baby spinach ranged from 48.2 to 92.1 mg per 3.5 oz (100 g) across eight USDA samples, a spread of 64 percent around the mean. — USDA Foundation Foods, baby spinach, 8 samples (n = 8 samples) Evidence E source
  Calcium mean 68.35 mg, range 48.2 to 92.1 mg, spread 64 percent; beta-carotene mean 3400 ug, range 3030 to 4000 ug, spread 29 percent

What a real portion looks like

• A cup of raw spinach weighs only 0.88 oz (25 g) in the USDA survey portion table, and the salad guideline amount is 50 g. — US survey food portions, raw spinach, FNDDS food code 72125100 Evidence E source
  1 cup 25 g, 1 leaf 10 g, 1 baby leaf 1 g, guideline amount in salad 50 g, quantity not specified 13 g

What your body absorbs

• In a crossover iron isotope trial, adding 1.26 g of oxalate to a kale meal left nonhaem iron absorption unchanged at 11.5 percent against 10.7 percent without it. — 16 healthy women aged 18 to 45, two randomized crossover stable isotope studies, 13 completed both (n = 16) Evidence B source
  Iron absorption 10.7 percent with kale, 11.5 percent with kale plus 1.26 g oxalate, P=0.86; spinach meal 24 percent lower than kale, P>0.16
• In a crossover trial in 19 women, fractional calcium absorption from two green vegetables was 0.391 and 0.476 against 0.552 from milk. — 19 healthy Thai women aged 20 to 45, three-way randomized crossover, calcium load about 100 mg (n = 19) Evidence B source
  Winged bean 0.391 +/- 0.128, ivy gourd 0.476 +/- 0.109, milk 0.552 +/- 0.119, both vegetables lower than milk at P<0.05
• By the NIH fact sheet, the body takes up only 4 to 17 percent as much phylloquinone from spinach as from a tablet, and eating the vegetable with fat improves uptake. — NIH Office of Dietary Supplements vitamin K fact sheet for health professionals Evidence E source
  4 to 17 percent of the absorption seen from a tablet

What cooking and storage change

• Boiling greens under a cover of water and draining keeps 55 percent of vitamin C and 60 percent of folate, against 60 and 65 percent when little water is used. — USDA retention factors, food group Vegetables and Vegetable Products, greens boiled and drained Evidence E source
  Water cover drained: vitamin C 55 percent, folate 60 percent, thiamin 80 percent; little water drained: vitamin C 60 percent, folate 65 percent, thiamin 85 percent

What it does to your health

• A meta-analysis of 118 randomized trials found a trivial benefit of nitrate-rich foods for endurance (SMD 0.15), driven by beetroot, with no benefit for red spinach or Swiss chard. — 118 randomized controlled trials of nitrate, polyphenol, L-arginine and L-citrulline rich foods (n = 118 RCTs) Evidence A source
  Nitrate SMD 0.15 and polyphenol SMD 0.17, both p<0.001; no effect for red spinach, Swiss chard, rhubarb or L-citrulline
• Pooled cohort data link each extra daily serving of green leafy vegetables with 18 percent lower dementia risk in adults aged 45 and over. — 18,339 adults aged 45 and over in three cohorts, 936 dementia cases over 7 to 13 years, pooled with 13 earlier cohorts (n = 18,339 in three cohorts, 222,108 in the meta-analysis) Evidence C source
  Green leafy vegetables pooled HR per serving 0.82 (95% CI 0.70, 0.96), total fruit and vegetables highest against lowest HR 0.80 (95% CI 0.71, 0.91)
• Pooled cohort data link green leafy vegetable intake with 7 percent lower incidence of cardiovascular events. — 17 cohort studies of green leafy vegetable intake and incident cardiovascular disease (n = 17 studies) Evidence C source
  Pooled RR 0.93 (95% CI 0.92 to 0.95), cerebral infarction RR 0.92 (0.88 to 0.96), heart disease RR 0.93 (0.87 to 0.99)

Safety, limits and interactions

• Eating 6 oz (170 g) of spinach in a warm meal every day for 11 days left kidney, liver, cardiovascular, inflammation and iron markers unchanged in healthy adults. — 24 healthy adults aged 18 to 50, randomized parallel trial, 11 consecutive days (n = 24) Evidence B source
  No significant differences in blood and urine biomarkers between the two vegetable groups

What people believe that the data does not support

• A systematic review of 11 studies found no support for telling people on vitamin K antagonists to cut down on green leafy vegetables. — two dietary interventional trials and nine observational studies in patients on vitamin K antagonists (n = 11 studies) Evidence C source
  Conflicting results, an effect on coagulation detected only above about 150 micrograms of vitamin K a day
• The EU register lists zero authorized claims for spinach, and the claim that a red and green spinach blend protects blood lipids from oxidative damage stands as non-authorized. — EU register of nutrition and health claims, snapshot 2026-09-21, six spinach entries Evidence E source
  0 authorized, 6 non-authorized entries mentioning spinach

Who this works differently for

• EFSA states that for some young children eating leafy vegetables high in nitrate a risk of methaemoglobinemia cannot be excluded. — children eating leafy vegetables, EFSA CONTAM Panel statement of 9 December 2010 Evidence E source
  Qualitative risk statement, no dose given on the page
• Across 35 studies of wastewater-irrigated crops, spinach held a pooled mean of 2.86 mg/kg of cadmium, above the EU safety limit of 0.2 to 0.3 mg/kg. — 35 studies of wastewater irrigation, soils and edible crops published between 2000 and 2021 (n = 35 studies) Evidence C source
  Spinach pooled mean cadmium 2.86 mg/kg, more than 9.5 times the EU limit of 0.2 to 0.3 mg/kg, health risk index above 1 for most crops
• NIH names spinach as the first of the most common US sources of vitamin K and advises people on warfarin to keep their vitamin K intake consistent, since sudden changes can raise or lower the drug's effect. — people taking warfarin and similar vitamin K antagonist anticoagulants Evidence E source
  Sudden changes in vitamin K intake can raise or lower the anticoagulant effect

What is still unknown

• Across the same 118 randomized trials the authors state that food sources, dosage and duration still need study, and that it stays unknown whether women respond differently to nitrate-rich foods. — 118 randomized controlled trials of nitrate and polyphenol rich foods (n = 118 RCTs) Evidence A source
  Open questions named by the authors, no estimate

The bottom line

Cooking takes a cut of the water soluble vitamins, and how much depends on the water. Boiled under a cover of water and drained, greens keep 55 percent of vitamin C and 60 percent of folate by the USDA retention table, against 60 and 65 percent with little water, and that factor covers the greens group rather than spinach. The table is dated 1975. The oxalate story is less settled than its reputation. In a randomized crossover isotope study in 16 healthy women aged 18 to 45, adding 1.26 g of oxalate to a kale meal left nonhaem iron absorption unchanged, 11.5 percent against 10.7 percent without it (P = 0.86). The spinach meal in that same work absorbed 24 percent less iron than the kale meal, and that difference did not reach significance. For calcium there is no spinach measurement on this page. The nearest trial, in 19 healthy Thai women given a load of about 100 mg of calcium, put fractional absorption at 0.391 from winged bean and 0.476 from ivy gourd against 0.552 from milk, and spinach was not among the foods it tested. Two observational syntheses sit on the benefit side, and both report associations. Each extra daily serving of green leafy vegetables went with 18 percent lower dementia risk (pooled HR 0.82, 95 percent CI 0.70 to 0.96) in 18,339 adults aged 45 and over followed 7 to 13 years, pooled with 13 earlier cohorts. Across 17 cohort studies, green leafy vegetable intake went with 7 percent lower incidence of cardiovascular events (RR 0.93, 95 percent CI 0.92 to 0.95), pooled under a fixed effect model despite possible heterogeneity. Tolerance has been tested once and briefly. Twenty-four healthy adults aged 18 to 50 ate 6 oz (170 g) of spinach in a warm meal every day for 11 days, and their kidney, liver, cardiovascular, inflammation and iron markers showed no significant change. In that trial spinach was the comparison arm for duckweed, and 11 days is too short to speak for years of eating. Two cautions belong to particular people. EFSA states that for some young children eating leafy vegetables high in nitrate a risk of methaemoglobinemia cannot be excluded, in an agency statement that gives no dose. Across 35 studies of crops irrigated with untreated wastewater, spinach held a pooled mean of 2.86 mg/kg of cadmium, more than 9.5 times the EU limit of 0.2 to 0.3 mg/kg, and those are contaminated fields rather than ordinary shop spinach. For people on warfarin or other vitamin K antagonists, one systematic review of 11 studies, two dietary trials and nine observational studies, found the available evidence does not support advice to change diet when starting these drugs, and restricting vitamin K did not look like a valid way to improve anticoagulation quality. That is not evidence that a sudden large change in greens is harmless. The results inside that review conflict, and an effect on coagulation showed up above about 150 micrograms of vitamin K a day, while 3.5 oz (100 g) of raw mature spinach lists 394 micrograms. The 170 g a day of the tolerance trial above was tested in healthy adults, not in people on these drugs, and this page has no evidence card on what a change in greens does to someone already taking them. The EU register lists the claim that a blend of red and green spinach and chicory and chard protects blood lipids from oxidative damage as non-authorized, which means the evidence fell short when it was assessed. The authors of the 118 trial synthesis name the gaps themselves: which food sources, at what dose, for how long, and whether women respond differently.

Sources

1. grsp-daily-r5-01 · food composition dataset
   Spinach, mature, raw (CoFID 13-572): Calcium (mg) 170, Iron (mg) 2.10, Magnesium (mg) 54, Folate (ug) 114, Vitamin C (mg) 26, Vitamin K1 (ug) 394.00
   CoFID 2021, Public Health England, code 13-572 · checked 2026-09-25
2. grsp-daily-r5-02 · food composition dataset
   Spinach, baby: Calcium, Ca 68.35 MG range 48.2-92.1 (median 70.4), 8 samples, spread 64%; Carotene, beta 3400.0 UG range 3030.0-4000.0 (median 3330.5), 8 samples, spread 29%
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-09-25
3. grsp-daily-r5-03 · survey portion dataset
   Spinach, raw (FNDDS 72125100, fdc_id 2709614): 1 cup 25 g, 1 leaf 10 g, 1 baby leaf 1 g, Guideline amount in salad 50 g, Quantity not specified 13 g
   USDA FNDDS, food code 72125100, fdc_id 2709614 · checked 2026-09-25
4. grsp-daily-r5-05 · randomized crossover trial
   After normalization for the spinach reference meal absorption, geometric mean iron absorption from wheat bread rolls with kale (10.7%) did not differ significantly from wheat rolls with kale plus 1.26 g OA added as potassium oxalate (11.5%, P=0.86).
   Eur J Clin Nutr, 2008 · checked 2026-09-25
5. grsp-daily-r5-06 · randomized crossover trial
   Fractional calcium absorption (X+/- SD) was 0.391 +/- 0.128 from winged beans, 0.476 +/- 0.109 from ivy gourd, and 0.552 +/- 0.119 from milk.
   J Food Sci, 2008 · checked 2026-09-25
6. grsp-daily-r5-07 · fact sheet
   Phylloquinone in plant foods is tightly bound to chloroplasts, so it is less bioavailable than that from oils or dietary supplements [1]. For example, the body absorbs only 4% to 17% as much phylloquinone from spinach as from a tablet [2].
   NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-09-25
7. grsp-daily-r5-04 · retention factor dataset
   VEG,GREENS,BOILED,WATER COVER DRAIN (USDA-RETN-R6:3005): vitamin_c_mg 55%, folate_total_ug 60%, thiamin_mg 80%; VEG,GREENS,BOILD,LITTLE WATER DRAIN (USDA-RETN-R6:3004): vitamin_c_mg 60%, folate_total_ug 65%, thiamin_mg 85%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Code 3004 and 3005 · checked 2026-09-25
8. grsp-daily-r5-08 · meta-analysis of RCTs
   Trivial but significant benefits were demonstrated for consumption of nitrate and polyphenol-rich foods (SMD=0.15 and 0.17, respectively, p<0.001), including performance in time-trial, time-to-exhaustion and intermittent-type tests, and following both acute and multiple-day supplementation, but no effect of nitrate or polyphenol consumption was found in females. ... Among nitrate-rich foods, beneficial effects were seen for beetroot, but not red spinach or Swiss chard and rhubarb.
   J Int Soc Sports Nutr, 2021 · checked 2026-09-25
9. grsp-daily-r5-09 · meta-analysis of cohorts
   Additionally, green leafy vegetables demonstrated a protective association (pooled HR per serving increment: 0.82; 95% CI: 0.70, 0.96, P-trend = 0.015).
   Am J Clin Nutr, 2026 · checked 2026-09-25
10. grsp-daily-r5-10 · meta-analysis of cohorts
    The pooled RR (95% CI) of incident CVD events from 17 studies was 0.93 (0.92-0.95).
    Cardiovasc J Afr, 2021 · checked 2026-09-25
11. grsp-daily-r5-11 · randomized controlled trial
    Twenty-four healthy adults consumed either L. minor plant material or spinach as vegetable (170 g fresh weight) as part of a warm meal on 11 consecutively days in a randomized controlled parallel trial design. ... Both intervention groups did not show significant differences for these biomarkers.
    Plant Foods Hum Nutr, 2022 · checked 2026-09-25
12. grsp-daily-r5-13 · systematic review
    The available evidence does not support current advice to modify dietary habits when starting therapy with VKAs. Restriction of dietary vitamin K intake does not seem to be a valid strategy to improve anticoagulation quality with VKAs.
    Medicine (Baltimore), 2016 · checked 2026-09-25
13. grsp-daily-r5-14 · claim register
    POL-HC-8442 A combination of red spinach, green spinach, red chicory, green chicory, green leaf chard, red leaf chard, red Swiss chard, golden Swiss chard and white Swiss chard Contributes to the protection of blood lipids from oxidative damage -/- Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-8442, snapshot 2026-09-21 · checked 2026-09-25
14. grsp-daily-r5-12 · agency statement
    In these cases, the Panel considers that for some young children the possibility of a risk of methaemoglobinaemia cannot be excluded.
    EFSA, EFSA assesses possible health risk for children from nitrate in leafy vegetables, 2010 · checked 2026-09-25
15. grsp-daily-r5-15 · meta-analysis of contamination data
    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 2026-09-25
16. sf-vkw-5 · agency advice
    The most common sources of vitamin K in the U.S. diet are spinach; broccoli; iceberg lettuce; and fats and oils, particularly soybean and canola oil [5,7]. ...These drugs antagonize the activity of vitamin K, leading to the depletion of vitamin K-dependent clotting factors. People taking warfarin and similar anticoagulants need to maintain a consistent intake of vitamin K from food and supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect [45].
    NIH Office of Dietary Supplements, Vitamin K Fact Sheet for Health Professionals · checked 2026-10-08
17. grsp-daily-r5-16 · meta-analysis of RCTs
    Further research into food sources, dosage and supplementation duration to optimise the ergogenic response to polyphenol consumption is warranted. Further studies should evaluate whether differential sex-based responses to nitrate and polyphenol consumption are attributable to physiological differences or sample size limitations.
    J Int Soc Sports Nutr, 2021 · checked 2026-09-25