The Vitamin K Content in Green Tea
When examining what tea has vitamin K, green tea is often the first to be mentioned. It is true that the dried leaves of the Camellia sinensis plant, used to make green tea, contain significant quantities of vitamin K1 (phylloquinone). A study from the Journal of the Academy of Nutrition and Dietetics reported that dried green tea leaves contained a higher amount of vitamin K1 per 100 grams compared to dried black tea leaves. However, this is only part of the story.
Vitamin K and the Brewing Process
Vitamin K is a fat-soluble vitamin, meaning it does not dissolve well in water. This is why the brewing process, which uses hot water to steep the leaves, extracts only a minimal amount of the vitamin from the leaves into the final beverage. Research confirms that brewed green tea is not a significant dietary source of vitamin K1. For the average, moderate tea drinker, the vitamin K content in a cup of brewed green tea is generally considered negligible and won't impact their overall intake.
High Consumption and Warfarin Interactions
Despite the low concentration in a single cup, excessive consumption of green tea has been known to interfere with anticoagulant medications like warfarin. There are documented cases where patients on warfarin who drank very large quantities of green tea (half a gallon to a full gallon daily) experienced a decrease in their International Normalized Ratio (INR), a measure of blood clotting. For most people, this is not a concern, but it is a critical consideration for those taking blood thinners.
Black Tea and Other True Teas
Black tea, which also comes from the Camellia sinensis plant, contains vitamin K in its dried leaf form, although typically less than green tea. Similar to green tea, the vitamin K in black tea is not effectively transferred to the water during brewing. Therefore, a standard cup of brewed black tea is also not a meaningful source of vitamin K. Oolong and white teas, from the same plant, follow this same principle.
Dandelion Tea: A Notable Herbal Exception
When exploring herbal teas, the situation is different and depends heavily on the plant used. Dandelion is one of the most prominent examples of a plant known to be rich in vitamin K, especially its greens. A single cup of raw dandelion greens contains several times the recommended daily dose of vitamin K. While the vitamin K content in a brewed dandelion tea will be less than in the raw greens, a tea made from dandelion leaves or roots may still contain a more significant amount than standard green or black tea, depending on the concentration. This makes it a potential factor for individuals on blood thinners.
Other Herbal Teas
For many other herbal teas, such as chamomile or mint, the vitamin K content in the brewed form is also negligible. Some herbs, like mint, have been noted to have vitamin K in their raw state. However, the extraction during brewing remains inefficient. Some herbal teas may also be a source of K2, the type of vitamin K produced by gut bacteria and found in fermented foods, but this is distinct from the K1 found in plants.
Comparison of Vitamin K Content
To illustrate the difference, the following table compares the vitamin K1 content of dried leaves versus the brewed infusion, based on available research.
| Sample | Dried Leaf/Grain (μg/100g) | Brewed Infusion (μg/100g) |
|---|---|---|
| Green Tea | 482 ± 81 | 0.03 ± 0.02 |
| Black Tea | 312 ± 3.9 | 0.02 ± 0.001 |
| Dandelion Greens | Up to 428 | Variable, more than true teas |
| Chamomile Tea | Not specified | 0 |
This table highlights why a person on warfarin is primarily concerned with consuming the leaves, not simply drinking the brewed liquid. The difference in concentration is several orders of magnitude.
Implications for Individuals on Blood Thinners
For most people, the vitamin K in tea is not a dietary concern. However, for those on anticoagulant medications like warfarin, it is crucial to understand these distinctions. Consuming large, inconsistent amounts of green tea or certain potent herbal preparations can alter blood clotting and interfere with medication effectiveness. Physicians and registered dietitians often advise maintaining a consistent daily intake of vitamin K, rather than completely avoiding it. Anyone with health concerns should consult their doctor before making significant dietary changes, including incorporating large amounts of any herbal tea.
The Final Word on Tea and Vitamin K
Ultimately, a typical cup of brewed tea—whether green, black, or most herbals—contains a negligible amount of vitamin K. This is because vitamin K is fat-soluble and does not readily extract into water during the brewing process. While the dried leaves of green and black tea contain the vitamin, and certain herbs like dandelion are rich in it, the final beverage is not a significant dietary source. The only exceptions are cases of extremely high consumption or specialized preparations using potent herbs.
Conclusion
While dried tea leaves, especially green tea, contain vitamin K, the brewing process prevents the vast majority of this nutrient from ending up in your cup. The fat-soluble nature of vitamin K means that standard, moderate tea consumption does not significantly contribute to your daily intake. Herbal teas, particularly those from dandelion greens, may contain more, but most brewed varieties remain low. For individuals on blood-thinning medication, it is high-volume green tea consumption that has been linked to potential issues, not normal daily intake. Always consult a healthcare professional regarding dietary changes if you are on medication. The core lesson is to differentiate between the nutritional content of the raw plant and the brewed liquid to understand what tea has vitamin K.
