Vitamin K Content in Leafy Greens
Yes, leafy greens are the most abundant dietary source of vitamin K1 (phylloquinone) and should be considered the primary food source for meeting vitamin K requirements. 1
Nutritional Evidence
Leafy greens represent the richest natural source of vitamin K available in the diet. According to the 2022 ESPEN micronutrient guidelines, the most abundant nutritional sources of vitamin K are leafy greens, cruciferous vegetables, asparagus, prunes, peas, and parsley, with leafy greens listed first as the predominant source. 1
Specific Vitamin K Content
Green leafy vegetables constitute the major source of vitamin K in the diet, providing the highest concentrations of phylloquinone (vitamin K1) among all food categories. 2
Raw spinach contains 144.9 μg vitamin K per cup, while frozen cooked spinach contains 1027.3 μg per cup, demonstrating that processing can significantly increase vitamin K concentration. 1
The majority of dietary vitamin K is obtained from a few leafy green vegetables along with certain vegetable oils (soybean, cottonseed, canola, and olive oils). 3
Most foods contain very low vitamin K content (<10 μg/100 g), making leafy greens particularly important as concentrated sources. 3
Clinical Relevance for Vitamin K Requirements
The adequate intake (AI) for vitamin K is 1 mg/kg body weight per day according to EFSA, or 120 mg for male adults and 90 mg for female adults according to IOM. 1
Mean intake of young adults is approximately 80 μg phylloquinone/day, while older adults consume approximately 150 μg/day, indicating that many individuals may not meet optimal requirements without consuming leafy greens. 3
Green leafy vegetables are particularly rich in vitamin K1, which has large effects on osteoblasts and osteocalcin metabolism, contributing to bone health beyond just coagulation function. 4
Important Clinical Considerations
For Patients on Anticoagulation
Patients using vitamin K antagonists (warfarin) should maintain consistent intake of leafy greens rather than avoiding them entirely. 1
An increase in dietary vitamin K intake may result in subtherapeutic INR, increasing the risk for thromboembolic events, while sudden decreases can cause excessive anticoagulation. 1
The most common dietary sources of vitamin K are dark green vegetables, and caregivers should be educated about foods high in vitamin K to develop a plan involving consistency in vitamin K intake from week to week. 1
Maintenance of stable anticoagulation control is possible through dose titration and patient counseling if the patient's vitamin K intake is known. 1
Absorption and Bioavailability
Absorption of phylloquinone from a food matrix is poor, meaning that despite high vitamin K content, the actual bioavailability from leafy greens may be limited. 3
Vitamin K is fat-soluble, so consuming leafy greens with dietary fat improves absorption. 1
Conditions with fat malabsorption (celiac disease, cystic fibrosis, short bowel syndrome) are common causes of vitamin K deficiency despite adequate dietary intake. 1
Additional Dietary Sources
While leafy greens are the primary source, other vegetables and oils also contribute:
Cruciferous vegetables, asparagus, prunes, peas, and parsley are additional plant-based sources. 1
Vegetable oils (soybean, cottonseed, canola, olive) contain high amounts, with soybean oil containing up to 193 μg vitamin K/100 g. 1, 3
Green leafy vegetables are particularly rich in minerals (iron, calcium, zinc) and vitamins (beta carotene, vitamin E, K, B, and C), making them valuable beyond just vitamin K content. 5