Vitamin K1: Why It Matters and How to Get Enough
Vitamin K1, also known as phylloquinone, is a fat-soluble vitamin essential for blood clotting and bone health. While most people get adequate K1 from food, athletes and active individuals benefit from understanding how this vitamin works and when supplementation makes sense.
This guide is for anyone who wants to understand K1's role in the body, recognize deficiency signs, and make informed supplement choices.
TL;DR
- Vitamin K1 is the primary vitamin regulating blood clotting
- Best food sources: dark leafy greens (kale, spinach, broccoli)
- Recommended daily intake for adults: 90–120 µg (Booth, 2012)
- Fat-soluble — absorbs better with dietary fat
- Deficiency is rare, but anticoagulants can affect levels
- Athletes may need more due to higher bone stress
How Vitamin K1 Works
Vitamin K1 functions as a coenzyme in carboxylase reactions, activating clotting factors (factors II, VII, IX, and X). Without sufficient K1, your body cannot produce functional clotting proteins (Shearer and Newman, 2008).
Beyond blood clotting, K1 participates in activating osteocalcin — a protein that binds calcium in bone tissue. Research shows that adequate K1 intake is associated with lower fracture risk (Booth et al., 2000).
Bioavailability
K1 bioavailability from food varies significantly. From raw leafy vegetables, it is only 5–10%, but adding fat significantly improves absorption (Gijsbers et al., 1996). Supplemental K1 absorbs much better — approximately 80% (Shearer and Newman, 2008).
Best Food Sources
| Food | K1 Content (µg/100g) | Notes |
|---|---|---|
| Kale | 817 | Best natural source |
| Spinach | 483 | Widely available |
| Broccoli | 141 | Holds up well when cooked |
| Brussels sprouts | 177 | Good winter option |
| Parsley | 1640 | Use as garnish |
| Soybean oil | 184 | For cooking |
Recommended Dosage
| Group | Dose (µg/day) | Notes |
|---|---|---|
| Women 19+ | 90 | EFSA recommendation |
| Men 19+ | 120 | EFSA recommendation |
| Athletes | 120–200 | Higher bone stress (Tsugawa et al., 2006) |
| Pregnant | 90 | Consult your doctor |
Important: If you take blood thinners (e.g., warfarin), talk to your doctor before taking K1 supplements. Vitamin K1 can reduce the effectiveness of these medications.
When to Consider a Supplement
Most people get enough K1 from food. A supplement may help if you:
1. Eat few vegetables — limited leafy green intake
2. Have fat malabsorption issues — celiac disease, Crohn's disease
3. Take long-term antibiotics — these can disrupt gut K-vitamin production
4. Train intensely — to compensate for higher bone stress
MaxFit offers multivitamins and standalone K-vitamin supplements that meet European quality standards.
K1 vs K2: What's the Difference?
| Property | K1 (Phylloquinone) | K2 (Menaquinone) |
|---|---|---|
| Primary function | Blood clotting | Directing calcium into bones |
| Main sources | Leafy vegetables | Fermented foods, animal products |
| Half-life | 1–2 hours | Up to 72 hours (MK-7) |
| Best for | Clotting support | Bone and heart health |
Both forms are important but serve different roles. Many quality supplements contain both. Read more in our Vitamin K2 guide.
Common Mistakes
1. Taking K1 without fat — as a fat-soluble vitamin, it needs dietary fat for absorption. Take with meals.
2. Ignoring warfarin-K1 interactions — this can be dangerous. Always consult your doctor.
3. Confusing K1 and K2 — they are different compounds with different functions.
4. Fearing overdose — no toxicity from dietary K1 has been documented (Booth, 2012).
Frequently Asked Questions
Can you overdose on vitamin K1?
No cases of toxicity from dietary vitamin K1 have been documented in the scientific literature. For supplements, follow manufacturer guidelines (Booth, 2012).
Does vitamin K1 help prevent fractures?
The Framingham study found that low K1 intake was associated with higher fracture risk. Adequate intake (>90 µg/day) was associated with better bone mineral density (Booth et al., 2000).
Do athletes need more vitamin K1?
Some studies suggest that intense training may increase K-vitamin needs due to greater bone stress (Tsugawa et al., 2006). At least 120 µg per day is recommended.
Is vitamin K1 suitable for vegans?
Yes — the best K1 sources are plant-based (leafy greens). It is one of the few vitamins that vegans naturally get in abundance.
Estonia-Specific Considerations
In Estonia's climate, fresh leafy greens are less available during winter months, but frozen spinach and broccoli retain most of their K1 content. Estonian dietary guidelines recommend 75–120 µg of K1 per day for adults. During winter, adding a multivitamin may be sensible, especially when vegetable intake is limited.
References
1. Booth SL. (2012). Vitamin K: food composition and dietary intakes. Food & Nutrition Research, 56(1), 5505.
2. Booth SL, Tucker KL, Chen H, et al. (2000). Dietary vitamin K intakes are associated with hip fracture but not with bone mineral density in elderly men and women. American Journal of Clinical Nutrition, 71(5), 1201-1208.
3. Shearer MJ, Newman P. (2008). Metabolism and cell biology of vitamin K. Thrombosis and Haemostasis, 100(4), 530-547.
4. Gijsbers BL, Jie KS, Vermeer C. (1996). Effect of food composition on vitamin K absorption in human volunteers. British Journal of Nutrition, 76(2), 223-229.
5. Tsugawa N, Shiraki M, Suhara Y, et al. (2006). Vitamin K status of healthy Japanese women: age-related vitamin K requirement for gamma-carboxylation of osteocalcin. American Journal of Clinical Nutrition, 83(2), 380-386.
Browse MaxFit's vitamin K supplements and find the right product for you.
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