Dear Dietitian,
Thank you for your recent article on vitamin D and COVID-19. There is so much information out there, and I appreciate your common-sense approach. Recently, I’ve read about studies on vitamin K and COVID-19. Is there a connection?
David
Dear David,
Thank you for your kind words. It sounds like you have been doing your homework! Vitamin K has made headlines recently for a possible link to the novel virus, COVID-19. There are two main types of this vitamin: K1 and K2. K1 is the main dietary source and is found naturally in dark green, leafy vegetables, such as spinach, kale, green leaf lettuce and broccoli. K2 is primarily bacterial in origin, and is produced in the human intestines. It is also found in modest amounts in fermented foods like sauerkraut and natto, a soy dish. Meat, cheese, and beef liver are animal sources of K2.
The primary function of vitamin K is blood clotting, or coagulating. Its name is derived from the German “Koagulations” vitamin. When you suffer a cut on your finger, it’s vitamin K’s job to help that wound stop bleeding.
Recent research points to a possible link between vitamin K and heart and lung health. These studies are early in their conception, and many more are needed before a sound scientific conclusion can be made. Vitamin K has also been indicated in bone health, but studies are conflicting. There isn’t enough evidence to recommend supplementing vitamin K for osteoporosis.
An observational study in the Netherlands found a possible link to low levels of vitamin K and severe cases of COVID. Scientists suggest that poor Vitamin K status may be linked to the breakdown of lung tissues, which is often seen in patients with severe cases of COVID (1). Remember that observational studies do not show cause and effect, and more research is needed to explore the possible link.
We are blessed to have a rich food supply in America, and most of us obtain adequate amounts of vitamin K in our diet. Consequently, vitamin K deficiencies in adults are very rare. Vitamin K is stored in body fat, so if you don’t consume enough of it one day, you have reserves to draw from. While it is possible to take too much of a fat-stored vitamin, vitamin K toxicities are extremely rare.
There is not enough data for a Recommend Daily Allowance (RDA) of vitamin K. In this case, an Adequate Intake (AI) is established. The AI for men is 120 micrograms (mcg) per day, and women should consume 90 mcg per day.
The table below lists foods that contain vitamin K.
| Food | Vitamin K content (micrograms) |
| Kale, raw (1 cup) | 548 |
| Spinach, cooked (1/2 cup) | 444 |
| Lettuce, green leaf (1 cup) | 97 |
| Collard greens, cooked (1/2 cup) | 418 |
| Turnip greens, cooked (1/2 cup) | 265 |
| Broccoli, cooked (1/2 cup) | 110 |
Does vitamin K help prevent severe cases of COVID-19? Frankly, we need more information. Supplementing vitamin K is not recommended since most Americans get enough of this nutrient in their diets. If you are taking Coumadin® (warfarin), DO NOT supplement Vitamin K, as it can interfere with the action of warfarin and increase the risk of a stroke. Talk to your doctor if you have more questions about Vitamin K.
Until next time, be healthy!
Dear Dietitian
References
1. Dofferhoff, A.S.; Piscaer, I.; Schurgers, L.J.; Walk, J.; van den Ouweland, J.M.; Hackeng, T.M.; de Jong, P.A.; Gosens, R.; Lux, P.; van Daal, H.; Maassen, C.; Maassen, E.G.; Kistemaker, L.E.; Vermeer, C.; Wouters, E.F.; Janssen, R. Reduced Vitamin K Status as A Potentially Modifiable Prognostic Risk Factor in COVID19. Preprints 2020, 2020040457 (doi: 10.20944/preprints202004.0457.v2)
