Adult women need 90 micrograms (mcg) of vitamin K per day, and adult men need 120 mcg. These values, set by the National Institutes of Health, apply to all adults 19 and older, including during pregnancy and breastfeeding. Most people can hit these targets with a single serving of leafy greens, though the specific amount varies by age, and certain medications make consistency just as important as quantity.
Daily Intake by Age and Sex
Vitamin K recommendations are set as “Adequate Intakes” rather than Recommended Dietary Allowances, which means there wasn’t enough data to establish a precise average requirement. Still, these are the numbers nutrition experts use as targets:
- Birth to 6 months: 2.0 mcg
- 7 to 12 months: 2.5 mcg
- 1 to 3 years: 30 mcg
- 4 to 8 years: 55 mcg
- 9 to 13 years: 60 mcg
- 14 to 18 years: 75 mcg
- Adult women (19+): 90 mcg
- Adult men (19+): 120 mcg
Pregnancy and breastfeeding don’t change the requirement. Pregnant or nursing women follow the same targets for their age group: 75 mcg for those 14 to 18, and 90 mcg for those 19 and older.
K1 vs. K2: What Counts Toward Your Daily Target
Vitamin K comes in two main forms. K1 (phylloquinone) is found in plant foods, especially green vegetables, and makes up the majority of what most people eat. K2 (menaquinones) shows up in fermented foods, some cheeses, and animal products, and is also produced by bacteria in your gut. The official daily intake values don’t distinguish between the two forms. Both contribute to your total.
K1 is primarily used by your liver to make proteins that help blood clot. K2 appears to play a larger role in directing calcium into bones and away from blood vessels. Research on K2 supplements for bone health has used doses well above the standard adequate intake. In studies of postmenopausal women, doses of 180 mcg per day of one K2 form (MK-7) slowed age-related bone loss over three years, while higher doses of another form (MK-4) at 15 to 45 mg per day influenced bone turnover markers in a dose-dependent way. These are supplemental doses studied in clinical trials, not general dietary recommendations.
Best Food Sources of Vitamin K
Leafy greens are by far the richest sources. A single half-cup of cooked spinach delivers about 445 mcg, nearly five times the daily target for women and close to four times the target for men. Cooked Swiss chard provides 572 mcg per cup. Even a cup of raw spinach gives you 145 mcg. You don’t need to eat large quantities of greens to meet your needs.
Other high-vitamin-K foods (over 100 mcg per serving):
- Collard greens, cooked from frozen: 530 mcg per half cup
- Turnip greens, cooked from frozen: 425 mcg per half cup
- Mustard greens, cooked: 415 mcg per half cup
- Beet greens, cooked: 350 mcg per half cup
- Kale, cooked: 247 mcg per half cup
- Broccoli, cooked: 110 mcg per half cup
- Brussels sprouts, cooked: 109 mcg per half cup
If you’re not a big greens eater, moderate sources can add up. A cup of shredded romaine lettuce has 48 mcg. A half cup of cooked asparagus has 46 mcg. A kiwi has 30 mcg. Even a tablespoon of raw parsley contributes 62 mcg. Oils also contain small amounts: a tablespoon of soybean oil has 25 mcg, olive oil about 8 mcg.
Fruits, root vegetables, and most grains are relatively low in vitamin K. A cup of grapes has 22 mcg, a medium pear about 8 mcg, and a half cup of carrots around 10 mcg. These foods contribute something, but greens do the heavy lifting.
No Known Upper Limit for Toxicity
There is no established tolerable upper intake level for vitamin K. Unlike vitamins A and D, which can build up to toxic levels, naturally occurring vitamin K from food has not been shown to cause harm at high doses in healthy people. This is partly why a single serving of spinach can deliver several times the daily target without concern.
That said, the absence of a formal upper limit doesn’t mean more is always better, especially if you take blood-thinning medication.
Why Consistency Matters on Blood Thinners
If you take warfarin (a common blood thinner), vitamin K intake is a serious practical concern. Warfarin works by blocking vitamin K’s role in clotting. Eating significantly more vitamin K than usual can reduce the drug’s effectiveness and increase clotting risk. Eating significantly less than usual can make the drug too potent and raise bleeding risk.
The goal is not to avoid vitamin K. It’s to keep your intake steady from day to day and week to week. If you normally eat a salad with romaine lettuce at lunch, keep doing that. If you want to start eating kale regularly, or stop eating it, let your prescriber know first so they can adjust your dose. The same applies to multivitamins, which vary in their vitamin K content between brands. If you take one, take it every day and don’t switch brands without a conversation with your provider.
Signs of Vitamin K Deficiency
Deficiency is uncommon in healthy adults who eat a varied diet, but it does happen, particularly in people with conditions that impair fat absorption (since vitamin K is fat-soluble), those on long-term antibiotics that disrupt gut bacteria, or newborns who have very low vitamin K stores at birth.
The hallmark symptom is unusual bleeding. This can show up as easy bruising, nosebleeds, bleeding gums, blood in urine or stool, or tarry black stools. In newborns, deficiency can cause life-threatening bleeding in or around the brain, which is why infants typically receive a vitamin K injection shortly after birth. Over time, low vitamin K may also weaken bones.
Diagnosis usually starts with blood tests that measure how quickly your blood clots. If clotting is slower than normal in someone with risk factors, vitamin K deficiency is a likely explanation. Direct measurement of blood vitamin K levels is possible but less commonly used.