Bok choy: a watery leaf whose calcium is well absorbed

Bok choy is 94.5% water, and its calcium is absorbed well. In a randomized three-way test in 15 women eating labeled vegetables as single meals, the fraction of calcium absorbed was 0.519 from bok choy stems and 0.520 from the leaves, close to broccoli at 0.478 and kale at 0.527. That was one small study of single meals. The amount on the plate is modest. Across 8 USDA samples, raw bok choy averaged 61.9 mg of calcium per 3.5 oz (100 g), with individual samples between 48.8 and 100 mg. The NIH Office of Dietary Supplements lists Chinese cabbage (bok choi) among the nondairy vegetable sources of calcium.

How much is actually in it

• Raw bok choy averages 61.9 mg of calcium per 3.5 oz (100 g) in USDA Foundation samples, but individual samples ranged from 48.8 to 100 mg. — USDA Foundation Foods samples of Cabbage, bok choy, raw (n = 8 samples) Evidence E source
  Calcium mean 61.93 mg per 3.5 oz (100 g), median 56.05, range 48.8-100.0 mg
• Raw bok choy averages 30.3 mg of vitamin C per 3.5 oz (100 g) across USDA Foundation samples, with a range from 16.2 to 43.8 mg. — USDA Foundation Foods samples of Cabbage, bok choy, raw (n = 8 samples) Evidence E source
  Vitamin C mean 30.3 mg per 3.5 oz (100 g), median 29.2, range 16.2-43.8 mg
• Raw bok choy is about 94.5% water and carries 227.8 mg of potassium, 68 micrograms of folate and 1.3 g of fiber per 3.5 oz (100 g) on USDA Foundation averages. — USDA Foundation Foods samples of Cabbage, bok choy, raw (n = 8 samples) Evidence E source
  Water 94.54 g (92.78-96.1); potassium 227.8 mg (165-280); folate 68 micrograms (56-100); fiber 1.26 g (0.77-2.61); protein 1.02 g per 3.5 oz (100 g)

What a real portion looks like

• Among 347 healthy women in Shanghai, habitual Brassica intake averaged 98.3 g a day, mostly as bok choy. — 347 healthy Chinese women in the Shanghai Breast Cancer Study, food frequency questionnaire over prior 5 years (n = 347) Evidence C source
  Mean Brassica intake 98.3 g per day, primarily bok choy

What your body absorbs

• The NIH Office of Dietary Supplements names Chinese cabbage (bok choi) among nondairy vegetable sources of calcium. — general population, US fact sheet Evidence E source
  No effect size; source listing and bioavailability statement
• In a randomized three-way comparison in 15 women, about 52% of the calcium in bok choy stems and leaves was absorbed, close to broccoli (48%) and kale (53%). — 15 normal women, single test meals of intrinsically labeled vegetables, about 83 mg calcium each (n = 15) Evidence B source
  Fractional absorption 0.519 +/- 0.089 (stems), 0.520 +/- 0.074 (leaves); milk reference 0.463 +/- 0.095
• In Filipino schoolchildren fed carrots, pechay (bok choy), squash and kangkong with 7, 15 or 29 g of fat a day for 9 weeks, the share with low liver vitamin A fell from 35% to 7%. — schoolchildren aged 9-12 in the Philippines, meals 3 times a day, 5 days a week for 9 weeks (n = 116 (39, 39, 38)) Evidence B source
  Total-body vitamin A pool about 2-fold in all three fat groups; low liver vitamin A prevalence 35% to 7%

What cooking and storage change

• Laboratory stir-frying of pak choi kept its glucosinolates even at the highest temperature tested. — pak choi (Brassica rapa ssp. chinensis) and Chinese cabbage samples, laboratory cooking Evidence D source
  Glucosinolates retained even at the highest temperature tested

What it does to your health

• Observational data link high Brassica vegetable intake with lower prostate cancer risk in 3 of 6 clearly interpretable studies, with one more borderline. — 12 published epidemiological studies on Brassica vegetables and prostate cancer, 6 clearly interpretable (n = 12 studies) Evidence C source
  3 of 6 significant risk reductions (P < 0.05), 1 borderline (P = 0.06)

Safety, limits and interactions

• A worldwide meta-analysis of vegetable nitrate and nitrite found bok choy among the highest, at a mean of 3,407 mg per kg, behind only rocket and mizuna. — published measurements of nitrate and nitrite in vegetables and fruits worldwide Evidence C source
  Bok choy mean 3407.40 mg/kg (95% CI 2841.39-3973.42)
• In China, pak choi supplied 33.9% of dietary cypermethrin intake overall and 30.7% for children, whose extreme exposure exceeded the acute reference dose. — Chinese population, 65,915 consumers aged 2-100 and 3,701 children aged 2-6, with 14,096 monitored samples from 2001-2006 (n = 65915) Evidence C source
  Pak choi 33.9% of cypermethrin intake (general), 30.7% (children); 99.99th percentile for children far above ARfD
• NIH lists green leafy vegetables, a group that includes bok choy, as a main food source of vitamin K and advises people on warfarin to keep vitamin K intake consistent rather than change it suddenly. — 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

The bottom line

The same 8 USDA samples averaged 30.3 mg of vitamin C per 3.5 oz (100 g), anywhere from 16.2 to 43.8 mg, along with 227.8 mg of potassium, 68 micrograms of folate and 1.26 g of fiber. Fiber varied most, from 0.77 to 2.61 g. In Shanghai, 347 healthy women reported eating 3.5 oz (98.3 g) of Brassica vegetables a day, mostly as bok choy, a self-reported figure for a Chinese diet. In a laboratory, stir-frying pak choi kept its glucosinolates even at the highest pan temperature tested, which is a food chemistry result with no people involved. For health outcomes we have only a 2002 review of Brassica vegetables as a group. Of 12 observational studies on prostate cancer, 6 could be clearly interpreted, and 3 of those found a significantly lower risk with high Brassica intake, with one more borderline (P = 0.06). There was no pooled estimate. In Filipino schoolchildren aged 9 to 12, meals with carrots, pechay (bok choy), squash and kangkong gave 4.2 mg of provitamin A carotenoids a day for 9 weeks with 7, 15 or 29 g of fat. The share with low liver vitamin A fell from 35% to 7%, and bok choy was one of four vegetables, so its own part is unknown. Two cautions come from the growing conditions. A worldwide meta-analysis of measured nitrate and nitrite put bok choy third among vegetables, at a mean of 3,407 mg per kg (95% CI 2,841 to 3,973), behind rocket and mizuna, with levels that depend on climate and fertilizer. We have no card on what that level means for infants, so this page cannot say whether bok choy is suitable for home-made baby food. In China in 2001 to 2006, pak choi supplied 33.9% of dietary cypermethrin pesticide intake for the general population and 30.7% for children aged 2 to 6. That figure is about pesticide residue on the crop, and children's extreme exposure exceeded the acute reference dose. We have no card on how washing or cooking changes that residue. We also have no card on the vitamin K in bok choy, on pregnancy, on kidney disease or on medicines such as warfarin, so this page cannot answer those questions. Anyone taking warfarin should ask the clinician who manages the dose before changing how much bok choy or other leafy greens they eat.

Sources

1. bkc-daily-r5-01 · USDA FoodData Central Foundation Foods, dataset
   Cabbage, bok choy, raw (FDC 2685572, Foundation Foods, release 2026-04-30): Calcium, Ca 61.93 mg per 100 g, range 48.8-100.0 (median 56.05), samples 8
   USDA FoodData Central, Foundation Foods, FDC 2685572 (release 2026-04-30) · checked 2026-09-29
2. bkc-daily-r5-02 · USDA FoodData Central Foundation Foods, dataset
   Cabbage, bok choy, raw (FDC 2685572, Foundation Foods, release 2026-04-30): Vitamin C, total ascorbic acid 30.3 mg per 100 g, range 16.2-43.8 (median 29.2), samples 8
   USDA FoodData Central, Foundation Foods, FDC 2685572 (release 2026-04-30) · checked 2026-09-29
3. bkc-daily-r5-03 · USDA FoodData Central Foundation Foods, dataset
   Cabbage, bok choy, raw (FDC 2685572, Foundation Foods, release 2026-04-30): Water 94.54 g (92.78-96.1); Potassium, K 227.8 mg (165.0-280.0); Folate, total 68.0 ug (56.0-100.0); Fiber, total dietary 1.259 g (0.77-2.61); Protein 1.02375 g per 100 g; samples 8
   USDA FoodData Central, Foundation Foods, FDC 2685572 (release 2026-04-30) · checked 2026-09-29
4. bkc-daily-r5-09 · cohort study
   Mean habitual Brassica intake was 98.3 g/day, primarily as bok choy, and Brassica intake significantly increased across quartile categories of ITC levels.
   Cancer Epidemiol Biomarkers Prev, 2003 · checked 2026-09-29
5. bkc-daily-r5-04 · agency fact sheet
   Nondairy sources include canned sardines and salmon with bones as well as certain vegetables, such as kale, broccoli, and Chinese cabbage (bok choi).
   NIH Office of Dietary Supplements, Calcium fact sheet for health professionals · checked 2026-09-29
6. bkc-daily-r5-05 · randomized crossover trial
   Absorption of calcium from three intrinsically labeled Brassica sp. vegetables was measured in 15 normal women in a three-way randomized design. ... Fractional calcium absorption from broccoli averaged 0.478 +/- 0.089, from bok choy stems, 0.519 +/- 0.089, from bok choy leaves, 0.520 +/- 0.074, and from kale 0.527 +/- 0.091.
   Heaney RP, Weaver CM et al., J Food Sci, 1993 · checked 2026-09-29
7. bkc-daily-r5-06 · randomized controlled trial
   The meals provided 4.2 mg provitamin A carotenoids/d (mainly beta-carotene) from yellow and green leafy vegetables [carrots, pechay (bok choy), squash, and kangkong (swamp cabbage)] and 7, 15, or 29 g fat/d (2.4, 5, or 10 g fat/meal) in groups A, B, and C (n = 39, 39, and 38, respectively). ... The overall prevalence of low liver vitamin A (<0.07 mumol/g) decreased from 35% to 7%.
   Am J Clin Nutr, 2007 · checked 2026-09-29
8. bkc-daily-r5-07 · laboratory cooking study
   Stir-frying retains the glucosinolates even at the highest temperature applied.
   Plant Foods Hum Nutr, 2017, 72:439-444 · checked 2026-09-29
9. bkc-daily-r5-10 · review of observational studies
   Twelve published studies give some information about Brassica vegetables and prostate cancer risk; six of these studies can be clearly interpreted. Of these, three reported statistically significant reduced risks (P < 0.05) and one reported a borderline significant reduced risk (P = 0.06) with high Brassica vegetable consumption.
   Nutr Cancer, 2002 · checked 2026-09-29
10. bkc-daily-r5-08 · meta-analysis of occurrence data
    The highest concentration (mean and 95%CI) of nitrate/nitrite was determined in Rocket (4825.15; 3044.14-6606.16), Mizuna (3500; 2702.48-4297.52), and Bok choy (3407.40; 2841.39-3973.42) in vegetable group
    Ecotoxicol Environ Saf, 2023 · checked 2026-09-29
11. bkc-daily-r5-11 · exposure assessment
    Pak-choi and Chinese cabbage contributed 33.9 and 13.2%, respectively, to the cypermethrin intake for the general population, while pak-choi and citrus covered 30.7 and 22.5% of the total intake for children, respectively.
    Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2011 · checked 2026-09-29
12. sf-vkw-3 · agency advice
    Food sources of phylloquinone include vegetables, especially green leafy vegetables, vegetable oils, and some fruits. ...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