Vitamin K: Comprehensive Guide to K1 and K2, Dietary Sources, Fermented Foods, and Gut Bacteria

Introduction

Vitamin K is an essential fat-soluble vitamin that plays a crucial role in blood clotting, bone metabolism, and heart health. It exists in two primary forms:

Vitamin K1 (phylloquinone): Found mainly in plant-based foods, particularly green leafy vegetables. It is crucial for blood coagulation.
Vitamin K2 (menaquinones): Found in animal products and fermented foods. It helps regulate calcium in the body, directing it to bones and teeth while preventing its accumulation in arteries.

This article explores the dietary sources of both Vitamin K1 and K2, the significance of fermented foods, and the contribution of gut bacteria to Vitamin K2 production.

1. Top Dietary Sources of Vitamin K1

Vitamin K1 is abundant in leafy greens, cruciferous vegetables, and certain plant-based oils. It is the primary dietary source of Vitamin K and plays a major role in blood coagulation. Here are some of the best food sources:

Leafy Green Vegetables (Highest in K1)

Kale: 1,062 mcg per cup (cooked)
Spinach: 889 mcg per cup (cooked)
Collard Greens: 772 mcg per cup (cooked)
Swiss Chard: 573 mcg per cup (cooked)

Cruciferous Vegetables

Broccoli: 220 mcg per cup (cooked)
Brussels Sprouts: 219 mcg per cup (cooked)
Cabbage: 76 mcg per cup (cooked)

Herbs (Surprisingly High in K1)

Parsley: 984 mcg per ½ cup
Basil: 130 mcg per tablespoon
Cilantro: 12 mcg per tablespoon

Plant-Based Oils (Moderate Sources of K1)

Soybean Oil: 25 mcg per tablespoon
Canola Oil: 17 mcg per tablespoon
Olive Oil: 8 mcg per tablespoon

2. Best Dietary Sources of Vitamin K2

Vitamin K2 is further divided into subtypes, primarily MK-4 (found in animal-based foods) and MK-7, MK-8, MK-9 (found in fermented foods). The richest dietary sources include:

Fermented Foods (High in MK-7, MK-8, MK-9)

Natto (Fermented Soybeans): 1,000 mcg per 3.5 oz (highest known source)
Fermented Cheeses (Gouda, Brie, Cheddar): 75 mcg per oz
Sauerkraut and Kimchi: Varies based on fermentation process

Animal Products (Rich in MK-4)

Organ Meats (Goose Liver, Chicken Liver): ~369 mcg per 100g
Egg Yolks: ~15 mcg per yolk
Butter (Grass-Fed): 15 mcg per tablespoon
Chicken, Beef, and Pork: 10–25 mcg per serving

3. The Role of Fermented Foods in Vitamin K2 Intake

Fermentation enhances the production of Vitamin K2, but not all fermented foods are equal.

Best Fermented Foods for K2

Natto: Unmatched source of MK-7, crucial for bone and heart health.
Cheese (Gouda, Brie, Edam): Provides MK-7 and MK-9.
Fermented Dairy (Kefir, Yogurt): Contains smaller amounts of MK-7.
Fermented Vegetables (Sauerkraut, Kimchi): May have K2 but in trace amounts.

If you’re looking to boost Vitamin K2 intake, natto and aged cheeses should be prioritized.

4. Can Gut Bacteria Produce Vitamin K2?

Yes, certain gut bacteria synthesize Vitamin K2, primarily MK-10 and MK-11. However, its contribution to overall K2 levels is limited due to:

Absorption Issues: Gut-produced K2 is absorbed in the colon, but the small intestine is more efficient at absorbing nutrients.
Microbiome Variability: The amount of K2 produced varies based on diet, antibiotics, and overall gut health.

Thus, while gut bacteria do contribute, dietary intake remains the most reliable source of Vitamin K2.

5. Health Benefits of Vitamin K1 and K2

Both Vitamin K1 and K2 offer numerous health benefits:

Vitamin K1 Benefits:

Essential for blood clotting (prevents excessive bleeding)
Supports liver function
Contributes to skin health and wound healing

Vitamin K2 Benefits:

Directs calcium to bones and teeth, reducing osteoporosis risk
Prevents arterial calcification, reducing heart disease risk
Supports brain function and cognitive health
May reduce wrinkles and improve skin elasticity

6. How Much Vitamin K Do You Need?

The recommended daily intake (RDI) varies by age and gender:

Adults (Male): 120 mcg/day
Adults (Female): 90 mcg/day
Pregnant/Breastfeeding Women: 90–120 mcg/day
Children (1-18 years): 30–75 mcg/day

No upper toxicity limit has been established, but excessive Vitamin K can interact with blood-thinning medications like warfarin.

7. Best Ways to Maximize Vitamin K Absorption

Vitamin K is fat-soluble, meaning it’s best absorbed with dietary fats. To optimize absorption:

Pair leafy greens with olive oil or avocado.
Eat fermented cheese with nuts or eggs.
Include butter or coconut oil when cooking vegetables.

8. Key Takeaways

Vitamin K1 is mainly found in leafy greens and herbs; it supports blood clotting.
Vitamin K2 is best sourced from natto, organ meats, and aged cheeses; it plays a role in bone and heart health.
Fermented foods, especially natto, are excellent sources of K2, but other fermented foods may provide only small amounts.
Gut bacteria produce some Vitamin K2, but dietary intake is more reliable.
Pair Vitamin K-rich foods with healthy fats to boost absorption.

Final Thoughts

Vitamin K is a powerhouse nutrient with significant health benefits. By incorporating both K1-rich plant foods and K2-rich animal or fermented foods into your diet, you can maximize its benefits for blood health, bone strength, and cardiovascular wellness. Always consult a healthcare provider before making major dietary changes, especially if you’re on blood thinners.

For the best results, aim for a balanced diet rich in both forms of Vitamin K to support overall well-being!