Is There Vitamin K in Seaweed? A Look at Marine Nutrients

November 7, 2025 •

4 min read

According to research, seaweed is a notable source of vitamin K, with some varieties offering a significant portion of the daily recommended value in a single serving. This marine vegetable, or more accurately, macroalgae, is packed with a wide range of nutrients, including this essential fat-soluble vitamin.

Quick Summary

Seaweed is a proven source of vitamin K, with varying concentrations depending on the species. Specific types like kelp and wakame offer substantial amounts of vitamin K1. Beyond this vitamin, seaweed provides numerous other nutrients, antioxidants, and fiber, contributing to overall health. It is a versatile addition to many meals.

Key Points

Source of Vitamin K: Seaweed contains vitamin K, particularly the K1 form (phylloquinone), and is a valuable addition to dietary sources.
Variety Matters: The concentration of vitamin K varies significantly by seaweed species, with brown seaweeds like kelp and wakame being among the most notable sources.
Essential for Health: Vitamin K is crucial for proper blood coagulation, bone metabolism, and may offer cardiovascular benefits.
Potential Interactions: Individuals on blood-thinning medication like warfarin should consult a doctor before increasing seaweed intake due to its vitamin K content.
Culinary Versatility: Seaweed can be incorporated into your diet in many ways, including dried snacks, flakes for seasoning, or in soups and salads.
Rich in Other Nutrients: Beyond vitamin K, seaweed is packed with other beneficial compounds, including iodine, iron, calcium, and antioxidants.

A Definitive Yes: Seaweed Contains Vitamin K

Yes, seaweed is a source of vitamin K, particularly vitamin K1 (phylloquinone). While leafy green vegetables are the most common and well-known source, certain seaweeds provide a valuable contribution to your daily intake. The concentration can differ significantly between species, with brown seaweeds like kelp and wakame often being highlighted for their content. This essential nutrient plays a crucial role in the body, primarily in blood coagulation and bone health. Including seaweed in your diet, even in small amounts, can help diversify your nutrient sources and ensure you're getting a broad spectrum of vitamins and minerals.

The Importance of Vitamin K in the Body

Before exploring the specific types of seaweed, it is useful to understand why vitamin K is so vital. It is a fat-soluble vitamin that the body needs for a variety of processes. The two main forms are K1 (phylloquinone) and K2 (menaquinone).

Blood Clotting: Vitamin K is a critical cofactor for proteins that regulate blood clotting. A deficiency can lead to an increased risk of uncontrolled bleeding.
Bone Metabolism: It also plays a key role in binding calcium in the bones, which is essential for maintaining strong and healthy bones and may reduce the risk of osteoporosis.
Cardiovascular Health: Some evidence suggests that vitamin K2 can help prevent the calcification of soft tissues, which is beneficial for cardiovascular health.

Which Seaweeds Contain the Most Vitamin K?

Not all seaweeds are created equal when it comes to vitamin K content. Research and nutritional data highlight several species as particularly good sources:

Kelp (Kombu): This large, brown seaweed is a rich source of vitamin K. One cup of kelp can offer a significant percentage of the daily value. It is often used to make stocks and broths, adding a mineral-rich boost to savory dishes.
Wakame: A popular type of seaweed used in salads and miso soup, wakame is also a reliable source of vitamin K. A small serving can provide a notable amount of this nutrient.
Nori: Best known for its use in sushi rolls, this type of red seaweed provides a source of vitamin K, though the amount can be modest depending on the serving size.

It is important to remember that nutrient levels can vary widely based on the species, growing conditions, and how the seaweed is prepared. Consuming a variety of different seaweeds can help ensure a broader nutritional intake.

Potential Risks and Considerations

While seaweed is a healthy food, there are some important considerations, especially for certain individuals.

Iodine Levels: Seaweed is famously high in iodine, which is crucial for thyroid function. However, excessive intake can lead to thyroid issues, so those with existing thyroid conditions should be cautious and monitor their intake.
Blood-Thinning Medication Interactions: Due to its vitamin K content, seaweed can interfere with the effectiveness of blood-thinning medications like warfarin. Individuals on such medication should maintain a consistent intake of vitamin K and consult their doctor before making significant dietary changes.
Heavy Metals: Depending on where it is harvested, seaweed can absorb heavy metals from its environment. Choosing organic and reputable sources can help mitigate this risk.

Incorporating Seaweed for Vitamin K and More

Adding seaweed to your diet is simple and can be a delicious way to boost your nutrient intake. Here are some practical tips:

Flavoring Agent: Use kelp or dulse flakes as a replacement for table salt to season dishes.
Snacks: Enjoy roasted nori sheets as a crispy, savory snack.
Salads and Soups: Add rehydrated wakame or arame to salads, or drop a strip of kombu into soups and broths for extra flavor and nutrients.
Smoothies: Blend kelp or spirulina powder into your smoothies for a vitamin and mineral boost.
Sushi and Wraps: Use nori sheets to create your own sushi rolls or healthy wraps.

Comparison of Seaweed Types and Vitamin K Content


Seaweed Type	Common Uses	Vitamin K Content (approximate)	Other Notable Nutrients
Wakame	Salads, Miso Soup	~7.2 mcg per 1/8 cup (raw)	Calcium, Magnesium, Folate
Kelp (Kombu)	Broths, Soups, Seasoning	~6.6 mcg per 1/8 cup (raw)	Very High Iodine, Folate, Iron
Nori	Sushi Wraps, Snacks	Variable, can be less concentrated	Iron, Iodine, Protein, B Vitamins
Dulse	'Vegan Bacon,' Seasoning	Less data available, but contains vitamin K	Magnesium, Iron, Antioxidants
Spirulina	Powdered Supplement	~12.7 mcg/g (dry weight)	Protein, Iron, B Vitamins

Conclusion

Seaweed is indeed a valuable and natural source of vitamin K, complementing other well-known sources like leafy green vegetables. The amount of vitamin K varies significantly by species, with kelp and wakame being reliable options. Beyond vitamin K, seaweed offers a wealth of other essential nutrients, including iodine, iron, calcium, and antioxidants, which contribute to its reputation as a superfood. It is a versatile ingredient that can be easily incorporated into a variety of dishes to boost nutritional intake. While it's important to be mindful of iodine levels and potential interactions with certain medications, seaweed remains a highly nutritious addition to a balanced diet. As the world continues to explore sustainable food sources, the potential of marine macroalgae as a nutritional powerhouse becomes ever more apparent.

Learn more about the diversity of nutrients in seaweed from this comprehensive review.

Frequently Asked Questions

Brown seaweeds, such as kelp and wakame, are generally known for having higher concentrations of vitamin K compared to other species. However, the exact amount can vary based on growing conditions.

Yes, because seaweed contains vitamin K, it can interfere with blood-thinning medications like warfarin. Patients on these medications should maintain a consistent intake of vitamin K and consult their doctor about any dietary changes.

The vitamin K from seaweed, like other dietary sources, primarily aids in proper blood coagulation (clotting) and is also essential for bone metabolism and binding calcium.

While some seaweeds like certain microalgae can be exceptionally high in vitamin K1, green vegetables like kale and spinach are typically considered the richest and most common dietary sources. Seaweed is a great complementary source.

Easy methods include using dried flakes as a seasoning, snacking on roasted nori sheets, making soup broth with kombu, or adding rehydrated wakame to salads.

Besides the potential interaction with blood thinners, excessive intake of seaweed can lead to too much iodine, which can cause thyroid issues. It's also important to source seaweed from clean environments to avoid heavy metal absorption.

Most edible seaweeds contain some amount of vitamin K, but the levels vary significantly. Brown seaweeds are often higher in concentration than red or green varieties, though green microalgae can also be a potent source.