Does Spirulina Contain Vitamin K? What to Know on Blood Thinners

For most people on a vitamin K antagonist, steady daily intake matters more than strict avoidance.

If you take warfarin or another vitamin K antagonist, you have probably been handed a printed list of foods to watch. Spirulina is a blue-green algae that looks and sounds very green, so it is reasonable to wonder whether it belongs on that list alongside kale and chard.

The honest answer has two halves. Spirulina does carry vitamin K1, and the amount is not zero. It is also small compared with the leafy vegetables most households already cook with, which changes the conversation from avoidance to consistency.

Does spirulina contain vitamin K?

Yes. Spirulina is a photosynthetic organism, and vitamin K1 is part of the photosynthetic machinery in anything that turns light into energy. Any green or blue-green food built around chlorophyll will carry some phylloquinone, and spirulina is no exception.

Published values cluster around 25 to 30 micrograms of vitamin K1 per 10 grams of dried spirulina, though numbers shift with strain, harvest and drying method. Treat any single figure as an approximation rather than a label guarantee, and ask the brand you buy from for their own assay if the exact number matters to your care plan.

How much vitamin K is in a daily spirulina serving?

Most people do not eat 10 grams of spirulina. A common daily serving sits at roughly 3 grams, which works out to about 10 tablets of ENERGYbits spirulina. At the midpoint of the published range, that is somewhere near 8 to 9 micrograms of vitamin K1.

For context, the adult daily value for vitamin K sits at 120 micrograms. So a standard spirulina serving contributes under a tenth of a day's worth. It is a real contribution, measurable and worth disclosing, but it is not the kind of number that tends to move an INR on its own.

How does spirulina compare with kale, spinach and other greens?

Context is the most useful thing a table can give you here. The figures below are approximate and will vary by variety, cooking method and portion size, but the ranking is stable across food databases.

A single cup of cooked kale carries well over a hundred times the vitamin K1 of a 3 gram spirulina serving. Even a cup of romaine, which is one of the lighter greens, comes in roughly five times higher. That is the practical scale most clinicians are already working with when they talk to you about greens.

Why does consistency matter more than avoidance?

Warfarin works by interfering with vitamin K recycling, so the dose is calibrated to your habitual vitamin K intake. Wild swings in that intake are what unsettle an INR. A steady, predictable amount, whether that amount is high or low, is easier to dose around than an erratic one.

This is why modern anticoagulation guidance leans toward consistency rather than elimination. If you decide, with your prescriber, to add spirulina, the useful move is to take the same amount at roughly the same time each day instead of three days on and four days off. The same logic applies to the broader question of how spirulina may interact with medications you already take.

Direct oral anticoagulants such as apixaban and rivaroxaban do not work through vitamin K, so dietary K is a different conversation for those drugs. Even then, tell your prescriber what you are adding. They are the only person with your full chart in front of them.

Does spirulina supply vitamin K2?

Not meaningfully. Vitamin K2, the menaquinone family that includes MK-4 and MK-7, comes mostly from fermented foods such as natto and from certain animal foods and cheeses. Spirulina is a K1 food, and anyone looking specifically for K2 will need to look elsewhere.

That distinction matters because K1 and K2 are often discussed interchangeably in supplement marketing. Spirulina's nutritional case rests on other things entirely: protein density, phycocyanin, iron and chlorophyll. If you are curious about where its other vitamin claims hold up, our piece on whether spirulina is a reliable B12 source walks through a similar nuance.

What should you ask your prescriber before starting spirulina?

Go in with specifics rather than a general question. Name the product, the daily gram amount, and the approximate vitamin K1 that amount represents. Ask whether they would like an extra INR check two to four weeks after you start, and whether they want you to hold off entirely.

It also helps to mention everything else in your routine at the same time, since stacking is where unexpected interactions usually hide. Our guide on taking spirulina alongside other supplements is a reasonable checklist to bring with you, and if your interest in algae started with circulation, the research summarized in what studies say about spirulina and heart health gives you the background your clinician may ask about.

If the answer is no for now, that is a legitimate answer. Anticoagulation is one of the few areas where the margin for improvisation is genuinely thin, and a cautious prescriber is doing their job.

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