Collard.
Collards are a leafy cabbage relative loaded with vitamin K, and their calcium isn't locked up by oxalate the way spinach's is, so more of it actually crosses your gut.
- Category
- Herb
What Collard is, and what it does.
- Does it work
- Suits anyone eating few dark leafy greens, and anyone getting calcium from plants. If you take a blood thinner, keep your greens intake steady and talk to your doctor.
- How much to take
- No supplement amount for collard is on record. As food, a cooked cup is the everyday serving, and eating it with fat is what carries the vitamin K and pigments across.
- Time to feel it
- Not something you feel on a clock. Vitamin K and lutein status shift over weeks of regular eating and show up on a blood panel or a macular pigment reading.
- The first dose
- Day one is a plate of greens. Absorption starts within hours, but the change registers as a blood level rather than as anything you notice at the table.
- With regular use
- Weeks of regular collards raise vitamin K and carotenoid intake and add steady dietary calcium. It's a slow build in nutrient status rather than a switch flipping.
- How well tolerated
- Well tolerated as a food. The high vitamin K load matters if you take a blood thinner, where a steady weekly intake matters more than a low one. Ask your doctor.
- How it feels
- Soft, slightly bitter, deeply savoury once braised. What you feel is a full and comfortable stomach rather than anything nutrient-specific.
- The overlooked benefit
- Long boiling leaches glucosinolates into the water and kills the enzyme that converts them, so a quick steam or a saute keeps far more of that chemistry intact.
The proof, claim by claim.
These words describe the research, not the molecule's worth. Research strength is how much work stands behind one claim, and it is never a product score.
- vitamin K intakeNarrative review
- calcium absorption from a low-oxalate greenRandomised trial
- lutein and zeaxanthin intake and macular pigment densityRandomised trial
- glucosinolate and isothiocyanate intakeIn vitro study
- green vegetable intake and blood pressure already in the normal rangeCohort study
Why these belong in the same formula. Each row says what the basis is, from settled biochemistry through to a trial that measured the pair.
Collard delivers vitamin K1 (phylloquinone), while MK-7 is a menaquinone. Both feed the same gamma-glutamyl carboxylase reaction that carboxylates glutamate residues on vitamin K-dependent proteins. They differ in half-life and tissue distribution rather than in the chemistry they enable. Anyone on a vitamin K antagonist should keep intake steady rather than variable, since it is the swing that matters.
Vitamin D raises the production of osteocalcin and matrix Gla protein, and vitamin K is the cofactor that carboxylates them so they can bind calcium. Collard supplies the K1 side of that pairing along with dietary calcium. The relationship is well established at the biochemical level. Bone density outcomes from food-level intakes are a separate question and less settled.
Collard leaf carries lutein and zeaxanthin in the chloroplast, and these are the same xanthophylls that concentrate in the macula. Supplemental lutein and dietary lutein share the same micellar absorption route and the same transport proteins. Taking both simply raises the pool from two directions. Absorption from raw leaf is low without fat and without cooking or chopping to disrupt the chloroplast.
Lutein, beta-carotene and phylloquinone from collard all need dietary lipid to form mixed micelles and cross the enterocyte. Eating the leaf with no fat leaves much of the carotenoid content unabsorbed. Long-chain fats do this more effectively than medium-chain ones because they drive chylomicron assembly, so olive or another long-chain oil is the closer match. The general principle holds for any added fat.
Brassica vegetables including collard contain glucosinolates that release thiocyanate on hydrolysis, and thiocyanate competes with iodide at the sodium-iodide symporter. This matters only when iodine intake is already low, and cooking reduces the effect substantially. At normal iodine intakes and normal serving sizes it is not a practical concern. It is worth flagging for people eating very large amounts of raw cruciferous leaf.
Collard is a cultivar of Brassica oleracea and carries glucosinolates including glucoraphanin, the direct precursor of sulforaphane. Myrosinase in the plant, released when the leaf is chopped or chewed, performs the hydrolysis. Boiling inactivates myrosinase, which is why cooking method changes the isothiocyanate yield more than the raw glucosinolate content does. Gut bacteria carry out some of the conversion when plant myrosinase is gone.
Collard is a low-oxalate green compared with spinach, so the calcium it contains is not locked into insoluble calcium oxalate. Measured fractional calcium absorption from low-oxalate Brassica greens is high, in the range reported for milk. This is a real distinction between leafy greens that is often collapsed into one category. The amount per serving is still modest compared with a dairy or supplement dose.
Collard contains both non-heme iron and ascorbate in the same leaf. Ascorbate reduces ferric to ferrous iron and keeps it soluble past the duodenum. Cooking degrades part of the ascorbate, so the internal pairing weakens with long boiling. Adding a separate vitamin C source at the meal restores the effect.
Collard carries beta-carotene alongside lutein in the same chloroplast membranes, and both compete for the same micellar and transport capacity. At high supplemental doses of one carotenoid the absorption of the others can fall, which is a known competition rather than a synergy. From food-level amounts in a mixed leaf this competition is not a practical problem. It becomes relevant when a single isolated carotenoid is dosed heavily.
Long-chain fats promote chylomicron formation, and phylloquinone and xanthophylls from collard ride out of the enterocyte in chylomicrons. Taking a leaf-derived carotenoid or a green-vegetable meal with an omega-3 oil raises the absorbed fraction relative to a fat-free meal. The mechanism is transport, not any interaction between the omega-3 and the carotenoid itself.
Nothing specific on file for Collard. Match the label to the daily amount above, and tell your doctor what you take.
Not medical advice. Show the label to your pharmacist.What Collard actually does.
Collard greens are the same plant species as kale, cabbage and broccoli, just bred for big open leaves, and it shares that family's typical makeup of glucosinolates, vitamin K and pigments, with less oxalate than spinach or chard.
The glucosinolates in the leaf are kept apart from the enzyme that activates them until you chop or chew the leaf, which brings them together and creates various breakdown products. Boiling deactivates that enzyme and washes the glucosinolates into the cooking water instead.
Vitamin K in collard is bound up inside the leaf's plant cell membranes, which is why you absorb little of it raw, and why cooking plus some added fat, which break down that membrane and give it a fat carrier, improves absorption.
Lutein and zeaxanthin in the leaf are pigments involved in photosynthesis, and once absorbed they travel on lipoproteins to the eye's macula, where they filter certain light and settle into the retinal membranes.
Where Collard comes from.
Collards are a leafy cabbage relative, the kind you'd braise. Two things make them worth knowing about: they're loaded with vitamin K, which matters a lot if you're on a blood thinner, and their calcium isn't locked up by oxalate the way spinach's is, so you actually absorb it. Eat them with some fat. The pigments and the vitamin K don't cross your gut wall without it.
Made from a plant. What ends up in the capsule tracks the harvest, so batch testing and a stated marker matter more here than with a made molecule.
Large flat leaves of the acephala (non-heading) group, harvested before the plant bolts. Cool weather raises sugar content and alters glucosinolate profile.
Heat inactivates myrosinase and softens cell walls. This is a deliberate compositional step, not incidental, since it changes which compounds the eater actually receives.
Low-temperature drying and milling gives leaf powder. Aqueous or hydroalcoholic extraction gives concentrates when a specific fraction is targeted.
Extracts are assayed by HPLC against a named marker, most often glucoraphanin or total lutein, because field variation in the raw leaf is wide.
Sold as a vegetable, as green-blend powder, or as a standardised extract in capsule form.
Getting Collard from food.
The whole-food sources on file. A supplement closes the gap, it does not replace dinner.
A gram-for-gram figure (how much of each you would eat to match a dose) will appear here once it is sourced and reviewed. This page will not print a number it cannot cite.
The forms it comes in.
The essence, in one line each.
- GC-MS profiling of Brassica oleracea identified the bioactive constituent classes present in the leaf material analysed.In vitro study. Ikuomola et al., 2025 (F1000Research). PMID 41098508 ↗
- Nutritional value, biochemical traits and growth of Brassica oleracea varied with red and blue light growing conditions, indicating that cultivation conditions shift leaf composition.In vitro study. Haghighi et al., 2025 (Plants). PMID 41375410 ↗
These are the studies our verdict leans on, chosen from the 2 we read for Collard. The full linked list is below.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. This information is for educational purposes only and is not intended to diagnose, treat, cure, or prevent any disease. Consult your healthcare provider before starting any supplement regimen.
