Kale: 325 percent on the label, 4.7 percent in the blood

Kale's vitamin K figure is the biggest number on any vegetable label we hold, 325 percent of the Daily Value per 100 grams. Seven people ate 400 grams of it with oil, with the vitamin K labelled so it could be tracked, and the modelled bioavailability came out at 4.7 percent. The peak arrived 6 to 10 hours later and then fell away. Vitamin K deficiency is rare and this does not mean kale fails to supply it. It means the percentage on a nutrition table describes the leaf rather than the person, and that gap is larger for kale than for almost anything else.

The numbers, per 100 g

How much is actually in it

• Less than a twentieth of kale's vitamin K actually reaches the blood. — 7 healthy volunteers, of whom 6 showed detectable labelled phylloquinone (n = 7) Evidence B source
  Plasma labelled phylloquinone peaked between 6 and 10 hours at an average of 2.1 nmol/L and then fell rapidly; modelled bioavailability of phylloquinone from kale was 4.7%; plasma and tissue half-times were 8.8 and 215 hours

What your body absorbs

• Iron absorption from kale was measurably better than from spinach, and the oxalate everyone blames was not the reason. — 16 apparently healthy women aged 18 to 45 under 60 kg, 13 completing both studies (n = 16 women, 13 completers) Evidence B source
  Absorption from bread with kale was 10.7% against 11.5% with kale plus 1.26 g of added potassium oxalate (p = 0.86); absorption from the spinach meal was 24% lower than from the kale meal without added oxalate, a difference that did not reach significance (p>0.16), and spinach was significantly higher in calcium and polyphenols than kale

What cooking and storage change

• Cooked kale protected cells from a carcinogen better than raw, and raw did something cooked did not. — 22 healthy subjects (n = 22) Evidence B source
  Cooked leaves reduced aflatoxin-induced DNA damage against baseline by 35% with metabolic activation and 33% without (p at or below 0.01), while raw leaves reduced it by 21% only in the activated condition and not significantly (p = 0.08); raw leaves significantly lowered plasma prostaglandin E2; plasma antioxidant capacity was unchanged in both
• Nobody can tell you how much of kale's active compound is in a given bunch, because measuring it cheaply is still an open problem. — published studies applying infrared spectroscopy to Brassica vegetables and oilseeds Evidence D source
  Near-infrared spectroscopy has been used to predict glucosinolates in broccoli, kale, rocket, cabbage, Brussels sprouts, brown mustard, rapeseed and pennycress, but only one study predicted isothiocyanates, in broccoli; the major limitation was the absence of critical evaluation of errors in the reference methods used for calibration

What it does to your health

• The equivalent of 340 grams of kale a day for twelve weeks lowered HbA1c in people with type 2 diabetes. — 30 patients with type 2 diabetes (n = 30) Evidence B source
  HbA1c, insulin resistance, body weight and calorie intake all fell significantly in the kale group against control, with positive trends in fasting blood glucose

What people believe that the data does not support

• The oestrogen-balancing effect attributed to kale and its relatives did not appear when it was tested directly. — 78 healthy premenopausal women aged 38 to 50 with a screening ratio of 3.0 or below (n = 78) Evidence B source
  Intention-to-treat analysis found no treatment effect (p = 0.9) and no treatment-by-time interaction (p = 0.6), with a significant time effect (p = 0.02); per-protocol analysis gave the same pattern (p = 1 for treatment)

The bottom line

Two beliefs about kale come apart when tested. Raw is not automatically better: cooked Ethiopian kale cut aflatoxin-induced DNA damage by a third while the raw version managed 21 percent and missed significance, though raw did lower an inflammatory marker that cooked did not. And the oestrogen story, that cruciferous vegetables shift hormone metabolism into a protective ratio, was tested head-on in 78 women for eight weeks and produced nothing at all. The trial worth knowing is the diabetes one: the equivalent of 341 grams of kale a day for twelve weeks lowered HbA1c and insulin resistance in 30 patients, and calorie intake fell too, which may be doing some of the work.

Sources

1. kal-dr-01 · stable isotope absorption study
   Modelling results demonstrated a mean (n 6) bioavailability of phylloquinone from kale to be 4.7%.
   Br J Nutr, 2010 · checked 2026-09-22
2. kal-dr-05 · randomised crossover stable isotope absorption study
   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 2026-09-22
3. kal-dr-02 · randomised controlled crossover trial
   Cooked B. carinata significantly reduced DNA damage induced by AFB1 as compared to baseline levels (+S9 mix: 35%, -S9 mix: 33%, p ≤ 0.01, respectively). Raw B. carinata only reduced DNA damage by S9-activated AFB1 by 21% (p = 0.08).
   Nutrients, 2018 · checked 2026-09-22
4. kal-dr-06 · systematic review of analytical methods
   Cruciferous vegetables and oilseeds are rich in glucosinolates that can transform into isothiocyanates upon enzymic hydrolysis during post-harvest handling, food preparation and/or digestion.
   Crit Rev Food Sci Nutr, 2024 · checked 2026-09-22
5. kal-dr-03 · randomised double-blind placebo-controlled trial
   A significant reduction in HbA1c, insulin resistance, body weight, and calorie intake was observed in the intervention group compared to control.
   Nutrients, 2024 · checked 2026-09-22
6. kal-dr-04 · randomised placebo-controlled trial
   Intent-to-treat repeated measures-ANOVA with multiple imputation (n=100) for missing values identified no treatment effect (P=0.9) or treatment-by-time interaction (P=0.6); however, a significant time effect was noted (P=0.02).
   Int J Vitam Nutr Res, 2024 · checked 2026-09-22