Vitamin K AI Table
| Life stage | AI (mcg/day) |
|---|---|
| Infant 0–6 mo | 2.0 |
| Infant 7–12 mo | 2.5 |
| 1–3 years | 30 |
| 4–8 years | 55 |
| 9–13 years | 60 |
| 14–18 years | 75 |
| 19+ years | 120 (M) / 90 (F) |
| Pregnancy | 90 (19+) |
| Lactation | 90 (19+) |
| Upper limit | none has been set |
| Food | Portion | mcg | %DV |
|---|---|---|---|
| Natto (K2, menaquinone) | 3 oz | 850 | 708% |
| Collards, frozen, boiled | 1/2 cup | 530 | 442% |
| Turnip greens, frozen, boiled | 1/2 cup | 426 | 355% |
| Spinach, raw | 1 cup | 145 | 121% |
| Kale, raw | 1 cup | 113 | 94% |
| Broccoli, boiled | 1/2 cup | 110 | 92% |
| Soybeans, roasted | 1/2 cup | 43 | 36% |
| Edamame, cooked | 1/2 cup | 21 | 18% |
| Iceberg lettuce, shredded | 1 cup | 14 | 12% |
| Egg, hard-boiled (MK-4) | 1 large | 4 | 3% |
Vitamin K is the only nutrient on this family of tables where the rows are AIs, not RDAs: the evidence is too thin to pin an exact requirement, so the NIH prints an Adequate Intake instead - 120 mcg a day for men, 90 for women. The practical targets land anyway: average Americans eat 138 and 122 mcg from food, which is why outright deficiency is essentially unheard of outside newborns.
The food story splits in two. Vitamin K1 (phylloquinone) lives in chloroplasts - the darker the green, the fuller the serving: cooked collards at 530 mcg per half cup, turnip greens 426, a cup of raw spinach 145. Vitamin K2 (menaquinone) lives in fermented and animal foods, and one of them laps the entire table: natto, the Japanese fermented soybean dish, delivers 850 mcg in 3 ounces - 708% of the Daily Value from K2 alone.
Two facts make vitamin K unusual. It has no known toxicity - no adverse effects from food or supplements have been reported in humans or animals, so no UL row exists. And it is the nutrient locked in a permanent standoff with warfarin: the drug works by blocking vitamin K's clotting role, so the clinical rule is not avoidance but consistency - same intake, day after day, so the dose stays calibrated.
How to use
- Read your row, with the AI caveat: 120 mcg for men and 90 for women from 19; 75 for teens 14-18; 60 at 9-13; 55 at 4-8 and 30 at 1-3; 2-2.5 mcg in infancy; pregnancy and breastfeeding stay at 90.
- Build the green half-cup habit: one serving of cooked collards or turnip greens clears an adult woman's AI several times over, and a cup of raw spinach or kale, half a cup of broccoli, or even iceberg lettuce adds up across a day - dress greens with oil, because K absorption improves with fat.
- If you take warfarin (or another vitamin K antagonist), do the opposite of avoidance: eat your usual greens in usual amounts every day, tell the clinic about any diet change, and let the dose track your routine - swinging intake swings your INR, which is the actual danger.
Frequently asked questions
How much vitamin K do I need per day?
The NIH sets Adequate Intakes, not RDAs, because healthy-group data is too sparse for an exact requirement: 120 mcg a day for men and 90 for women from 19; 75 for teens 14-18 (and during teen pregnancy/lactation); 60 for ages 9-13; 55 at 4-8; 30 at 1-3; and just 2-2.5 mcg in the first year. Adult pregnancy and breastfeeding stay at 90. Average intakes already sit at 138 mcg (men) and 122 (women), so the gap this table closes is habit, not amount.
What foods are highest in vitamin K?
Natto stands alone at 850 mcg per 3 ounces (708% of the Daily Value) - and it is K2, not the K1 the greens carry. The leafy ladder behind it: cooked collards 530 mcg per half cup (442%), frozen boiled turnip greens 426 (355%), raw spinach 1 cup 145 (121%), raw kale 113 (94%), boiled broccoli half cup 110 (92%). Then the shelf drops an order of magnitude: roasted soybeans 43, edamame 21, blueberries or iceberg lettuce 14, one hard-boiled egg just 4. Pattern: chloroplasts own the top of the K1 list; fermentation owns K2.
Can I eat leafy greens on warfarin?
Yes - the modern teaching is consistency, not elimination. Warfarin thins blood by antagonizing vitamin K, so your dose is calibrated against your habitual intake; suddenly dropping greens raises your INR, and suddenly bingeing them lowers it. What keeps you safe is a flat line: same amounts of vitamin K foods day after day, any diet change flagged to the anticoagulation clinic so they retest. The foods are not the problem; the swing is.
Why do newborns get a vitamin K shot?
Nature sets babies up short: vitamin K barely crosses the placenta, the newborn gut is too sterile to make it, and breast milk carries little - so every infant runs low for weeks. The result can be vitamin K deficiency bleeding, a rare but serious bleeding disorder that peaks 2-12 weeks out in exclusively breastfed babies. The American Academy of Pediatrics has recommended a single 0.5-1 mg intramuscular dose at birth since 1961, which reliably prevents it.
What is the difference between vitamin K1 and K2?
K1 (phylloquinone) comes from plants - it is the green in leafy greens - and is what most Americans eat. K2 covers a family of menaquinones (MK-4 through MK-13) from animal and fermented foods; natto is the outlier source, and the body also makes MK-4 from K1 directly, no bacteria required. Observational data credits K2 with heart and bone associations (the Rotterdam Study found high menaquinone intake linked to less coronary calcification), but the FDA has approved no health claims - Europe's regulator allows a bone-health claim for K alone. No toxicity exists for either form.