Vitamin K is the clotting and bone vitamin, and leafy greens supply most of it. The NIH Office of Dietary Supplements sets daily targets of 120 micrograms for men and 90 for women. A serving of kale or spinach comes close. Warfarin is the catch, and it makes consistency a medical matter.
Vitamin K often arrives on the same plate as foods that carry other nutrition debates. Related reading appears in the explainer on eggs and cholesterol, which sorts cohort findings from guidelines.
This article sits in the nutrition section, a running file on food science, labels, and everyday diets. Figures here come from named agencies and journals.
What Vitamin K Does in the Body
Vitamin K is a fat-soluble vitamin that works as a coenzyme. A coenzyme is a helper that an enzyme needs to run. Per the NIH, it powers the proteins that clot blood and build bone. Prothrombin, clotting factor II, is one of those proteins. Osteocalcin, a bone protein, depends on it too. For related coverage, see How Much Protein Do Adults Need? Daily Amounts, Explained.
Which Foods Carry Vitamin K1 and Vitamin K2
Two main forms sit on the plate. Phylloquinone, called vitamin K1, sits mainly in green leafy vegetables. The NIH names spinach, kale, broccoli, and lettuce, and lists vegetable oils alongside. Menaquinones, called vitamin K2, appear in animal-based and fermented foods. The standouts form a short list:
- Spinach, kale, broccoli, and lettuce for vitamin K1.
- Vegetable oils and fruits such as blueberries and figs for smaller K1 amounts.
- Natto, a fermented soybean dish, for the richest K2 load.
- Cheese, meat, eggs, and dairy for modest menaquinone levels.
Kitchen variety covers both forms easily. Spinach salads and broccoli sides stack the day quickly. Frozen greens count the same.
How Much Vitamin K Adults Need
The NIH Office of Dietary Supplements lists adequate intakes of 120 micrograms a day for men. Women carry a target of 90 micrograms, including pregnancy and breastfeeding. An adequate intake is a benchmark set from healthy population diets. It is not a strict requirement. Most people in the United States already reach it. Deficiency is rare in healthy adults.
What Studies Found About Bones
Bone findings arrive with mixed designs. A 2000 analysis in the American Journal of Clinical Nutrition drew on the Framingham Heart Study. Low vitamin K intake was associated with more hip fractures among 888 older adults. The top intake quartile showed a relative risk of 0.35 against the bottom. A 2013 randomized trial in Osteoporosis International found a bone effect. Taking 180 micrograms of menaquinone-7 daily for three years slowed density loss in 244 postmenopausal women. One trial does not settle the field.
What Remains Uncertain
Gut bacteria make menaquinones on their own, and the NIH notes their share is hard to measure. The 2000 cohort saw no link between intake and bone density itself, only fracture counts. Supplement evidence rests on limited trials at specific doses. Form, dose, and food matrix still lack head-to-head answers.
When to See a Clinician About Vitamin K
Warfarin sits at the center of the medical questions. The NIH explains that warfarin works against vitamin K. People on that drug and similar blood thinners need a steady intake from food and supplements. A clinician sets the dose to the usual diet. Planned reviews also fit long antibiotic courses or orlistat use. Bile acid sequestrants can cut absorption too. Unusual bleeding or easy bruising calls for prompt medical attention. We covered a connected angle in Sodium Intake Guidelines: How Much Is Too Much?.
Conclusion: Eat the Greens, Keep the Intake Steady
Vitamin K foods run from spinach and kale to natto and cheese, and they cover the NIH benchmarks of 120 micrograms for men and 90 for women. Bone evidence is encouraging but incomplete. The firm rule belongs to warfarin patients, whose intake must stay level. Greens often, consistency always.
