Broccoli and spinach: 5 percent of the calcium in spinach is absorbed

In 13 healthy adults given test meals carrying 200 mg of labeled calcium, 5.1 percent of the calcium in spinach was absorbed against 27.6 percent from milk, in a single-meal isotope study. On paper spinach holds more calcium than broccoli, 68 against 46 mg per 3.5 oz (100 g) in USDA samples, with much of the spinach calcium bound to oxalate. The NIH Office of Dietary Supplements reads the same work as showing that calcium from broccoli, kale and cabbage is absorbed about as well as from milk, though each serving holds much less of it. A second belief was tested directly. In randomized crossover isotope studies in 16 young women, adding the oxalic acid content of 5.3 oz (150 g) of spinach to a kale meal did not change iron absorption (11.5 against 10.7 percent, P = 0.86) in single test meals. The spinach meal itself absorbed 24 percent less iron than kale, a difference that did not reach significance. Broccoli leads on vitamin C, at 91 mg per 3.5 oz (100 g) raw in USDA samples against 27 to 30 mg in spinach, whose values spread widely. A cup is a poor unit for comparing them, because a cup of raw broccoli weighs 3.2 oz (90 g) and a cup of raw spinach 25 g.

How much is actually in it

• USDA samples put raw broccoli at about 91 mg vitamin C per 3.5 oz (100 g), roughly three times the 27 to 30 mg measured in baby and mature spinach. — USDA FoodData Central Foundation Foods: Broccoli, raw (5 samples); Spinach, baby and Spinach, mature (8 samples each) (n = 21 samples) Evidence E source
  Broccoli 91.3 mg/100 g (range 56.7-105.0); spinach baby 26.52 mg (9.87-54.7); spinach mature 30.27 mg (17.05-44.2)
• Per 100 g raw, USDA samples put spinach at 1.1 to 1.3 mg iron and 460 to 580 mg potassium, against 0.7 mg iron and 303 mg potassium in broccoli. — USDA Foundation Foods: Spinach, baby and Spinach, mature; Broccoli, raw (8 samples each) (n = 24 samples) Evidence E source
  Iron spinach baby 1.261 mg, mature 1.054 mg, broccoli 0.69 mg; potassium spinach baby 581.8 mg, mature 459.7 mg, broccoli 303.0 mg
• USDA samples show baby spinach far richer in beta-carotene (3400 vs 93 micrograms per 3.5 oz (100 g)) and somewhat richer in calcium (68 vs 46 mg) than raw broccoli. — USDA Foundation Foods: Spinach, baby (8 samples); Broccoli, raw (6-8 samples) (n = 16 samples) Evidence E source
  Beta-carotene 3400 vs 93 ug/100 g; calcium 68.35 vs 46.0 mg/100 g; broccoli vitamin K1 102 ug/100 g

What a real portion looks like

• In the USDA survey food table a cup of raw broccoli weighs 3.2 oz (90 g) but a cup of raw spinach only 25 g, so cup-for-cup comparisons favor broccoli. — USDA FNDDS household measures, Broccoli, raw (72201100) and Spinach, raw (72125100) Evidence E source
  Broccoli 1 cup 90 g, 1 floweret 10 g; spinach 1 cup 25 g, salad guideline amount 50 g

What your body absorbs

• In a randomized crossover trial in 13 adults, calcium absorption from spinach averaged 5.1% vs 27.6% from milk. — 13 healthy adults, test meals with 200 mg labeled calcium (n = 13) Evidence B source
  5.1% spinach vs 27.6% milk; within-subject difference 22.5 +/- 9.5%, P<0.0001
• According to NIH ODS, calcium from spinach is only about 5% absorbed, while calcium from broccoli, kale and cabbage is absorbed about as well as from milk. — general population Evidence E source
  Spinach 5% vs milk 27% (primary data: brsp-r6-06)

What cooking and storage change

• By the USDA retention table, greens boiled in covering water and drained keep 55% of vitamin C and 60% of folate, while steamed vegetables keep 85% of both. — USDA Table of Nutrient Retention Factors Release 6, group Vegetables and Vegetable Products, method codes 3005 and 3784, table dated Sep-75 Evidence E source
  Boiled greens: vitamin C 55%, folate 60%, potassium 85%; steamed other vegetables: vitamin C 85%, folate 85%, potassium 100%
• In a randomized crossover trial in 12 adults, adding 1 g mustard powder to 200 g cooked broccoli raised sulforaphane uptake more than fourfold (44.7 vs 9.8 umol/g creatinine). — 12 healthy adults, 24-hour urine after 200 g cooked broccoli with or without 1 g brown mustard powder (n = 12) Evidence B source
  Urinary SF-NAC 9.8 +/- 5.1 vs 44.7 +/- 33.9 umol per g creatinine

What it does to your health

• In a randomized crossover trial in 18 older adults with raised blood pressure, 300 g a day of cruciferous vegetable soup for 2 weeks lowered glycemic variability by 2.0% vs root and squash vegetables. — 18 non-diabetic adults with elevated blood pressure, median age 68, 89% women (n = 18) Evidence B source
  Glycemic variability MD -2.0% (95% CI -2.8 to -1.1); 2-h postprandial glucose -2.5 mg/dL (-0.14 mmol/L)

Safety, limits and interactions

• According to NIH ODS, spinach and broccoli are among the most common US sources of vitamin K, but the body absorbs only 4% to 17% as much from spinach as from a tablet. — US diet; relevant to people on warfarin who need steady vitamin K intake Evidence E source
  Spinach phylloquinone 4-17% of tablet absorption; fat with vegetables improves absorption
• Observational data link eight or more spinach servings a month with about 30% higher kidney stone risk in men and older women. — HPFS men and NHS I older women; 8+ spinach servings per month vs fewer than 1 (n = 138857) Evidence C source
  RR 1.30 (95% CI 1.08-1.58) men; RR 1.34 (95% CI 1.10-1.64) older women
• In a small uncontrolled study, eating 18 oz (500 g) broccoli daily for 6 days significantly raised the activity of CYP1A2, a drug-metabolizing enzyme, in men and women. — five men and five women, non-smokers, Jordan (n = 10) Evidence C source
  CYP1A2 activity after the broccoli diet: men 52.5 +/- 6.6, women 36.6 +/- 8.4 (P<0.005)

What people believe that the data does not support

• In randomized crossover isotope studies in young women, adding the oxalic acid content of 150 g spinach to a kale meal did not change iron absorption (11.5% vs 10.7%). — 16 healthy women aged 18-45 years, 13 completed both studies (n = 16) Evidence B source
  10.7% kale vs 11.5% kale plus 1.26 g oxalic acid, P=0.86; spinach meal 24% lower than kale, not significant
• The EU did not authorize a claim that broccoli helps maintain a healthy immune system. — EU nutrition and health claims register Evidence E source
  Status Non-authorized

Who this works differently for

• In a randomized crossover trial in 10 people eating 11 oz (300 g) broccoli soup, only 2% to 15% of glucoraphanin came out as sulforaphane in urine, varying by person. — 10 participants, three broccoli genotypes, plant myrosinase denatured in the soup (n = 10) Evidence B source
  24-h sulforaphane excretion 2-15% of glucoraphanin consumed; 3- and 5-fold higher plasma sulforaphane from high-glucoraphanin genotypes

What is still unknown

• Observational data from 12 cohorts (about 700,000 people) link higher broccoli intake with an 11% lower cancer risk, and the authors call for more cohort studies. — 12 cohort studies (699,482 individuals) and 23 case-control studies (n = 699482) Evidence C source
  Cohorts RR 0.89 (95% CI 0.82-0.96); case-control OR 0.64 (0.58-0.70)

The bottom line

Per 100 g raw, USDA samples put spinach at 1.1 to 1.3 mg iron and 460 to 580 mg potassium against 0.7 mg and 303 mg in broccoli, and a cup of raw spinach weighs far less than a cup of broccoli. Baby spinach held 3400 micrograms of beta-carotene per 3.5 oz (100 g) against 93 in broccoli. By the USDA retention table, greens boiled in water and drained keep 55 percent of vitamin C and 60 percent of folate, while steamed vegetables keep 85 percent of both, group factors never measured on these two vegetables. In 10 people eating 11 oz (300 g) of broccoli soup in which the plant enzyme myrosinase had been denatured, 2 to 15 percent of the glucoraphanin came out as sulforaphane in 24-hour urine, varying by person, in a very small trial. In 12 adults, adding 1 g of brown mustard powder to 7.1 oz (200 g) of cooked broccoli raised the urinary sulforaphane marker from 9.8 to 44.7 micromoles per gram of creatinine, a small study that measured a urine marker and no health outcome. In 18 adults with raised blood pressure, median age 68, a cruciferous vegetable soup eaten at 300 g a day for 2 weeks lowered glycemic variability by 2.0 percent (95% CI -2.8 to -1.1) against root and squash vegetables. That was a secondary outcome from mixed crucifers, and its clinical meaning is unclear. Observational data from 12 cohorts of about 700,000 people link higher broccoli intake with an 11 percent lower cancer risk (RR 0.89, 95% CI 0.82 to 0.96), an association the authors want tested in more cohort studies. The EU did not authorize a claim that broccoli helps maintain a healthy immune system. On safety, no card here tests either vegetable for harm directly, and three findings bear on it. According to the NIH Office of Dietary Supplements, spinach and broccoli are among the most common sources of vitamin K in the US diet, and the body absorbs only 4 to 17 percent as much from spinach as from a tablet. That matters to anyone on warfarin who needs a steady vitamin K intake. Observational data from 138,857 people link eight or more spinach servings a month, against fewer than one, with a higher kidney stone risk. The relative risk was 1.30 in men (95% CI 1.08 to 1.58) and 1.34 in older women (95% CI 1.10 to 1.64), with no association in younger women. In 10 non-smokers in Jordan eating 18 oz (500 g) of broccoli a day for 6 days, activity of CYP1A2, an enzyme that breaks down some drugs, rose significantly, to 52.5 in men and 36.6 in women after the broccoli diet. That study had no control group and tested no medicine.

Sources

1. brsp-r6-01 · food composition dataset
   Broccoli, raw: Vitamin C, total ascorbic acid 91.3 MG range 56.7-105.0 median 99.3 n=5 · Spinach, baby: 26.52 MG range 9.87-54.7 median 26.35 n=8 · Spinach, mature: 30.27 MG range 17.05-44.2 median 32.22 n=8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
2. brsp-r6-02 · food composition dataset
   Spinach, baby: Iron, Fe 1.261 MG range 1.02-1.6 n=8 · Potassium, K 581.8 MG range 433.0-700.0 n=8; Spinach, mature: Iron, Fe 1.054 MG range 0.63-1.62 n=8 · Potassium, K 459.7 MG range 320.0-644.0 n=8; Broccoli, raw: Iron, Fe 0.69 MG range 0.51-0.98 n=8 · Potassium, K 303.0 MG range 272.0-326.0 n=8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
3. brsp-r6-03 · food composition dataset
   Spinach, baby: Carotene, beta 3400.0 UG range 3030.0-4000.0 n=8 · Calcium, Ca 68.35 MG range 48.2-92.1 n=8; Broccoli, raw: Carotene, beta 93.0 UG range 54.0-118.0 n=6 · Calcium, Ca 46.0 MG range 34.0-58.0 n=8 · Vitamin K (phylloquinone) 102.0 UG range 76.6-136.0 n=8
   USDA FoodData Central, Foundation Foods, release 2026-04-30 · checked 2026-10-02
4. brsp-r6-04 · food survey portion dataset
   FNDDS 72201100 Broccoli, raw: 1 cup 90 g · 1 piece 10 g · 1 floweret 10 g · Quantity not specified 45 g; FNDDS 72125100 Spinach, raw: 1 cup 25 g · 1 leaf 10 g · 1 baby leaf 1 g · Guideline amount in salad 50 g
   USDA FNDDS 2021-2023, codes 72201100 and 72125100 · checked 2026-10-02
5. brsp-r6-06 · randomized 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 2026-10-02
6. brsp-r6-07 · agency fact sheet
   As a result, absorption of calcium is only 5% for spinach, whereas it is much higher, at 27%, for milk [3]. ... The bioavailability of calcium from other plants that do not contain these compounds—including broccoli, kale, and cabbage—is similar to that of milk, although the amount of calcium per serving is much lower [3].
   NIH Office of Dietary Supplements, Calcium Fact Sheet for Health Professionals (snapshot 2026) · checked 2026-10-02
7. brsp-r6-05 · retention factor dataset
   USDA-RETN-R6:3005 VEG,GREENS,BOILED,WATER COVER DRAIN: vitamin_c_mg 55% retained, folate_total_ug 60%, thiamin_mg 80%, potassium_mg 85%, iron_mg 95%; USDA-RETN-R6:3784 VEG,OTHER,STEAMED: vitamin_c_mg 85% retained, folate_total_ug 85%, thiamin_mg 90%, potassium_mg 100%, iron_mg 100%
   USDA Table of Nutrient Retention Factors, Release 6, 2007, Retn_Codes 3005 and 3784 · checked 2026-10-02
8. brsp-r6-10 · randomized crossover trial
   When study subjects ingested cooked broccoli alone, mean urinary SF-NAC excreted was 9.8 ± 5.1 μmol per g creatinine, and when cooked broccoli was consumed with mustard powder, this increased significantly to 44.7 ± 33.9 μmol SF-NAC per gram creatinine.
   Mol Nutr Food Res, 2018 · checked 2026-10-02
9. brsp-r6-12 · randomized crossover trial
   Glycaemic variability was lower in the active versus control (mean difference: -2.0%, 95% CI -2.8, -1.1, p < 0.001). Overall PPGR 2-h and AUC were lower in the active versus control (mean difference: -0.14 mmol/L, 95% CI -0.24, -0.04, p = 0.005 and -20.1 mmol/L × min, 95% CI -34.1, -6.1, p = 0.005, respectively), driven by the dinner PPGR (p = 0.004 and p = 0.003, respectively).
   Diabetes Obes Metab, 2025 · checked 2026-10-02
10. brsp-r6-08 · agency fact sheet
    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]. ... 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 Fact Sheet for Health Professionals (snapshot 2026) · checked 2026-10-02
11. brsp-r6-14 · prospective cohorts
    The relative risks for participants who ate eight or more servings of spinach per month compared with fewer than 1 serving per month were 1.30 (95% CI 1.08 to 1.58) for men and 1.34 (95% CI 1.10 to 1.64) for older women. Oxalate intake and spinach were not associated with risk in younger women.
    J Am Soc Nephrol, 2007 · checked 2026-10-02
12. brsp-r6-15 · nonrandomised trial
    These activities were significantly induced in both men (52.5+/-6.6) and women (36.6+/-8.4) after a standard diet of broccoli (P<0.005).
    Curr Drug Metab, 2007 · checked 2026-10-02
13. brsp-r6-09 · 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). 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 2026-10-02
14. brsp-r6-16 · regulatory register
    POL-HC-6817 Brassica olaracea var italica (broccoli) Helps maintain a healthy immune system. Non-authorised
    EU Register on nutrition and health claims, claim POL-HC-6817, snapshot 2026-09-21 · checked 2026-10-02
15. brsp-r6-11 · randomized crossover trial
    The percentage of sulforaphane excreted in 24 h relative to the amount of glucoraphanin consumed varies among volunteers from 2 to 15%, but does not depend on the broccoli genotype.
    Mol Nutr Food Res, 2018 · checked 2026-10-02
16. brsp-r6-13 · meta-analysis of observational studies
    The results suggest an inverse association between broccoli consumption and the risk of cancer both in case-control studies (OR: 0.64, 95% CI from 0.58 to 0.70, p < 0.001; Q = 35.97, p = 0.072, I2 = 30.49%-moderate heterogeneity; τ2 = 0.016) and cohort studies (RR: 0.89, 95% CI from 0.82 to 0.96, p = 0.003; Q = 13.51, p = 0.333, I2 = 11.21%-low heterogeneity; τ2 = 0.002). ... More studies, especially cohort studies, are necessary to clarify the possible beneficial effect of broccoli on several types of cancer.
    Nutrients, 2024 · checked 2026-10-02