Cabbage and spinach: two greens, two different catches

Cabbage and spinach share a shelf and very little else in the evidence. The finding with the most trials behind it belongs to cabbage. A meta-analysis of 23 dietary intervention trials found that cruciferous vegetables, cabbage among them, raise the activity of the drug-metabolizing enzyme CYP1A2 by 20 to 40%. Not all of those trials were randomized, and the clinical importance of that change has not been shown. Spinach is not a crucifer and was not part of it. Spinach meets medicines through vitamin K. NIH advises people on warfarin and similar anticoagulants to keep vitamin K intake steady, because sudden changes can raise or lower the drug's effect. Cabbage counts here too, with 59 mcg vitamin K per 3.5 oz (100 g) across 8 USDA samples of raw green cabbage. On paper baby spinach looks like a calcium food at 68 mg per 3.5 oz (100 g). In a crossover trial in 13 healthy adults, only 5.1% of the calcium in a spinach test meal was absorbed, against 27.6% from milk.

How much is actually in it

• In 8 USDA samples, raw baby spinach held 68 mg calcium, 582 mg potassium, 1.26 mg iron and 117 mcg folate per 3.5 oz (100 g). — 8 retail samples, USDA Foundation Foods (n = 8) Evidence E source
  Calcium 68.35 mg (48.2 to 92.1), potassium 581.8 mg (433 to 700), iron 1.261 mg (1.02 to 1.6), folate 116.5 mcg (90.4 to 155) per 3.5 oz (100 g)
• In 8 USDA samples, raw green cabbage held 42 mg calcium, 207 mg potassium, 40 mg vitamin C and 59 mcg vitamin K per 3.5 oz (100 g). — 8 retail samples, USDA Foundation Foods (n = 8) Evidence E source
  Calcium 41.84 mg (23.1 to 64.1), potassium 207.1 mg (184 to 267), vitamin C 40.34 mg (34.8 to 56.3), phylloquinone 59.4 mcg (41.6 to 82.9) per 3.5 oz (100 g)

What your body absorbs

• In a randomized crossover trial in 13 adults, only 5.1% of calcium from spinach was absorbed versus 27.6% from milk. — 13 healthy adults, single test meals with 200 mg calcium (n = 13) Evidence B source
  Absorption 5.1% spinach vs 27.6% milk; within-subject difference 22.5 +/- 9.5%
• Frozen spinach sold in New Zealand held 737 mg soluble oxalate per 3.5 oz (100 g), and 76.7% of its calcium was bound as insoluble oxalate. — 10 volunteers eating 3.5 oz (100 g) grilled spinach (n = 10) Evidence B source
  Soluble oxalate 736.6 mg/100 g; 76.7% of spinach calcium bound as insoluble oxalate
• In isotope trials in 16 women, adding oxalate to a kale meal did not change iron absorption (10.7% vs 11.5%), and absorption from a spinach meal was 24% lower but not significantly. — 16 healthy women aged 18 to 45, Zurich (n = 16) Evidence B source
  Iron absorption 10.7% kale vs 11.5% kale plus oxalate (P=0.86); spinach 24% lower than kale (P>0.16)
• According to NIH, the body absorbs only 4% to 17% as much vitamin K from spinach as from a tablet, and eating vegetables with some fat helps. — General population Evidence E source
  4% to 17% relative absorption

What cooking and storage change

• By the USDA retention table for boiled leafy greens drained with little water, about 60% of vitamin C and 65% of folate remain, against 95% of calcium and iron. — Vegetables and Vegetable Products group, greens boiled in little water and drained Evidence E source
  Retained: vitamin C 60%, folate 65%, potassium 90%, calcium 95%, iron 95%

What it does to your health

• Observational data link high intake of broccoli and cabbage with lower gastric cancer risk (RR 0.64). — 89 observational studies of cruciferous vegetables Evidence C source
  Gastric cancer RR 0.64 (95% CI 0.47 to 0.87) for broccoli and cabbage
• In two cohorts of about 250,000 adults, moderate plant nitrate intake, roughly a cup of baby spinach a day, was linked to 16% lower rates of fatty liver disease. — 53,854 Danish and 197,198 UK Biobank participants, 13.5 to 25.1 years (n = 251052) Evidence C source
  HR 0.84 (0.76 to 0.94), Q3 vs Q1 plant-sourced nitrate

Safety, limits and interactions

• A meta-analysis of 23 dietary intervention trials found cruciferous vegetables, including cabbage, raise CYP1A2 drug-metabolizing activity by 20% to 40%. — Humans in dietary intervention trials with broccoli, Brussels sprout, cabbage, cauliflower, radish, watercress (n = 23 trials) Evidence B source
  CYP1A2 activity +20 to 40%; GST-alpha +15 to 35%
• In Ethiopian farm and market surveys, parasites were found on 54.2% of raw spinach and 52.9% of raw cabbage samples. — 29 cross-sectional studies, 6659 vegetables and fruits, Ethiopia (n = 6659) Evidence C source
  Parasitic contamination: spinach 54.2%, cabbage 52.9%
• Spinach grown with untreated wastewater averaged 2.86 mg/kg cadmium across studies, over 9.5 times the EU limit, while treated wastewater kept levels near controls. — 35 studies of wastewater-irrigated soils and crops, 2000 to 2021 (n = 35 studies) Evidence C source
  Spinach pooled mean Cd 2.86 mg/kg vs EU limit 0.2 to 0.3 mg/kg

What people believe that the data does not support

• The EU refused to authorize a claim that a mix of black cabbage, chard, spinach and savoy cabbage protects blood lipids from oxidative damage. — EU labeling Evidence E source
  Non-authorized

Who this works differently for

• NIH advises people on warfarin to keep vitamin K intake steady, because sudden changes can raise or lower the drug's effect. — People taking warfarin and similar anticoagulants Evidence E source
  Direction only

The bottom line

Per 100 g raw, 8 USDA samples of baby spinach averaged 582 mg potassium, 1.26 mg iron and 117 mcg folate. Eight samples of green cabbage averaged 207 mg potassium and 40 mg vitamin C, and their calcium ranged from 23.1 to 64.1 mg around a mean of 42 mg. Oxalate explains part of the spinach calcium problem. Frozen spinach sold in New Zealand held 737 mg soluble oxalate per 3.5 oz (100 g), and 76.7% of its 90 mg of calcium was bound as insoluble oxalate. For iron, a trial in 16 women in Zurich found absorption from a spinach meal 24% lower than from a kale meal, a gap that did not reach significance. Adding oxalate to the kale meal did not change iron absorption (10.7% against 11.5%). Kale is a Brassica relative of cabbage, and head cabbage itself was not tested. The body takes up only 4% to 17% as much vitamin K from spinach as from a tablet, NIH says, and eating the vegetables with some fat improves it. Cooking costs vitamins more than minerals. By the USDA retention table for leafy greens boiled in a little water and drained, about 60% of vitamin C and 65% of folate remain, against 90% of potassium and 95% of calcium and iron. That is one factor for the whole group of greens, from a table dating to 1975. The health signals are observational. High intake of broccoli and cabbage, counted together, was linked to lower gastric cancer risk (RR 0.64, 95% CI 0.47 to 0.87) in a meta-analysis of observational studies. In two cohorts of 251,052 Danish and UK adults followed for 13.5 to 25.1 years, moderate nitrate intake from plants was linked to lower rates of fatty liver disease (HR 0.84, 0.76 to 0.94). The authors illustrate that level as about a cup of baby spinach a day, and the nitrate came from plants in general. The EU refused a claim that a mix of black cabbage, chard, spinach and savoy cabbage protects blood lipids from oxidative damage, and neither vegetable has an authorized claim in its register. Who should be careful. If you take warfarin, the NIH advice means keeping your spinach and cabbage intake steady from week to week and raising any big change with the person managing the drug. If you take a medicine cleared by CYP1A2, the cabbage finding above is worth mentioning to your prescriber, though its clinical effect is unproven. Contamination depends on where the greens grew. In 29 Ethiopian surveys of raw produce from farms and markets, parasites were found on 54.2% of spinach and 52.9% of cabbage samples, and washing was not assessed. Spinach irrigated with untreated wastewater averaged 2.86 mg/kg cadmium across studies, more than 9.5 times the EU limit of 0.2 to 0.3 mg/kg, which describes wastewater-irrigated crops only. We found no human study comparing cabbage with spinach directly.

Sources

1. casp-daily-r1-01 · dataset
   Spinach, baby (Foundation Foods 2026-04-30): Calcium, Ca 68.35 MG, range 48.2-92.1, samples 8; Potassium, K 581.8 MG, range 433.0-700.0, samples 8; Iron, Fe 1.261 MG, range 1.02-1.6, samples 8; Folate, total 116.5 UG, range 90.4-155.0, samples 8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 (Spinach, baby) · checked 2026-09-28
2. casp-daily-r1-02 · dataset
   Cabbage, green, raw (Foundation Foods 2026-04-30): Calcium, Ca 41.84 MG, range 23.1-64.1, samples 8; Potassium, K 207.1 MG, range 184.0-267.0, samples 8; Vitamin C, total ascorbic acid 40.34 MG, range 34.8-56.3, samples 8; Vitamin K (phylloquinone) 59.4 UG, range 41.6-82.9, samples 8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 (Cabbage, green, raw) · checked 2026-09-28
3. casp-daily-r1-04 · RCT
   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 2026-09-28
4. casp-daily-r1-05 · RCT
   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 frozen spinach contained 90mg total calcium/100g WM, 76.7%of this calcium was unavailable as it was bound to oxalate as insoluble oxalate.
   Asia Pac J Clin Nutr, 2003 · checked 2026-09-28
5. casp-daily-r1-06 · RCT
   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). Spinach was significantly higher in calcium and polyphenols than kale and absorption from the spinach meal was 24% lower compared to the kale meal without added OA, but the difference did not reach statistical significance (P>0.16).
   Eur J Clin Nutr, 2008 · checked 2026-09-28
6. casp-daily-r1-07 · fact sheet
   For example, the body absorbs only 4% to 17% as much phylloquinone from spinach as from a tablet [2]. Consuming vegetables at the same time as some fat improves phylloquinone absorption from the vegetables, but the amount absorbed is still lower than that from oils.
   NIH Office of Dietary Supplements, Vitamin K Health Professional Fact Sheet · checked 2026-09-28
7. casp-daily-r1-03 · dataset
   USDA-RETN-R6:3004 VEG,GREENS,BOILD,LITTLE WATER DRAIN, group Vegetables and Vegetable Products: vitamin_c_mg 60% retained, folate_total_ug 65%, potassium_mg 90%, calcium_mg 95%, iron_mg 95%
   USDA Table of Nutrient Retention Factors, Release 6 (2007), code 3004 · checked 2026-09-28
8. casp-daily-r1-10 · meta-analysis of observational studies
   High intake of broccoli and cabbage was associated with a decreased risk of gastric cancer (RR: 0.64; 95% CI: 0.47-0.87) and gallbladder cancer (RR: 0.46; 95% CI: 0.29-0.75).
   Crit Rev Food Sci Nutr, 2024 · checked 2026-09-28
9. casp-daily-r1-13 · cohort
   Moderate plant-sourced nitrate intake was associated with lower MASLD rates [pooled HRQ3vsQ1 (95%CI): 0.84 (0.76-0.94)] with similar patterns for plant- and vegetable-sourced nitrite. ... CONCLUSION: The health impact of nitrate and nitrite depends on source: moderate plant-sourced intakes (∼1 cup baby spinach/day) were linked to lower MASLD rates, while higher intakes from animal and additive sources were associated with higher rates.
   Clin Nutr, 2026 · checked 2026-09-28
10. casp-daily-r1-09 · meta-analysis of trials
    The meta-analyses performed demonstrated a significant effect on CYP1A2 and glutathione S-transferase-alpha (GST-α), with consumption of Cruciferae increasing the activities of these enzymes by 20-40% and 15-35%, respectively.
    Clin Pharmacol Ther, 2020 · checked 2026-09-28
11. casp-daily-r1-11 · meta-analysis of prevalence studies
    Lettuce (61.0%), salad (57.4%), spinach (54.2%), and cabbage (52.9%), were the vegetables most contaminated by parasites, while salad (73.8%), green pepper (35.3%), lettuce (26.0%), and cabbage (20.0%), were the most contaminated by bacteria.
    BMC Infect Dis, 2025 · checked 2026-09-28
12. casp-daily-r1-12 · meta-analysis
    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 2026-09-28
13. casp-daily-r1-14 · regulatory register
    POL-HC-8440 A combination of Tuscan black cabbage, ’tri-coloured‘ Swiss chard, ’bi-coloured‘ spinach and ’blu savoy‘ cabbage Contributes to the protection of blood lipids from oxidative damage -/- Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-8440, snapshot 2026-09-21 · checked 2026-09-28
14. casp-daily-r1-08 · fact sheet
    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 Health Professional Fact Sheet · checked 2026-09-28