Vitamin K1: What Your Result Means

What is Vitamin K1?

Vitamin K1 (phylloquinone) is the dietary form of vitamin K obtained from green leafy vegetables. The liver uses it to activate several clotting factors and bone proteins. Deficiency can slow clotting and raise bleeding risk; measuring it helps explain unexplained bruising, prolonged bleeding, or why PT/INR behaves unusually in someone with normal liver function.

Typical reference interval: Normal serum vitamin K1 is commonly roughly 0.1–2.5 ng/mL (assays vary widely). Low values with clinical signs (easy bruising, bleeding) are the ones that matter; interpretation always considers liver function and recent antibiotics.. Laboratories differ — the interval printed on YOUR report always governs.

If your Vitamin K1 is high

Common reasons Vitamin K1 runs above the reference interval:

• Supplement use — vitamin K1 supplements (or high-dose multivitamins) raise levels directly
• Frequent greens-heavy diet — high intake of spinach, kale, and broccoli reflects in the blood
• Sample timing — levels fluctuate with recent dietary intake

If your Vitamin K1 is low

Common reasons Vitamin K1 runs below the reference interval:

• Fat malabsorption — vitamin K is fat-soluble — celiac, Crohn's, or bile-flow problems impair uptake
• Long-term antibiotic use — broad-spectrum antibiotics kill gut bacteria that produce a share of vitamin K
• Diet chronically low in greens — a diet without leafy vegetables shortfalls K1 over time
• Liver disease — the liver must activate vitamin K into clotting factors
• Warfarin therapy — blood thinners block vitamin K recycling, which is their intended mechanism — expected low functional K

Symptoms worth knowing

The vitamin itself is silent. Deficiency shows as easy bruising, prolonged nosebleeds, heavier-than-usual bleeding from cuts, and — in infants — a rare bleeding condition. Because symptoms overlap with clotting disorders, the lab helps locate the cause.

What usually happens next

1. Low vitamin K with easy bruising warrants a clinical review — diet, gut, antibiotics, and medications are all candidates
2. Always interpret vitamin K with liver function (the liver activates it) and PT/INR
3. If you take a blood thinner, do NOT change vitamin K intake without your prescriber — stable intake is what they manage around

Frequently asked questions about Vitamin K1 results