Introduction:
Vitamin K is best known for its role in assisting blood to clot, or coagulate by allowing the body to produce proteins necessary for clotting. Vitamin K is a fat-soluble vitamin found in a number of foods, including leafy green vegetables. The chief source of vitamin K is produced by bacteria in the large intestine, and in most cases, absence of dietary vitamin K does not lead to health problems. Vitamin K deficiency is rare and is may be manifested as a tendency to bleed excessively. Additionally, vitamin K blocks the effects of the blood-thinning medication warfarin. In patients, taking warfarin, it is important to consume consistent amounts of vitamin K in the diet in order for the PTINR to attain and remain within stable range. Vitamin K supplements, or foods containing high amounts of vitamin K, should not be consumed with warfarin. Instead, a diet while on warfarin can include low to moderate amounts of vitamin K containing food sources as long as the same type and amount is consumed every day so that vitamin K intake remains consistently the same. The content of vitamin K in foods may be seen below by clicking the link to the Institute of Medicine website.
Vitamin K interactions:
Vitamin K and use of antibiotics: Vitamin K levels may be reduced by the use of any antibiotics, especially quinolones partly due to the reduction of gut flora which contributes to production of vitamin K. This may be especially be concerning when a patient is taking warfarin with antibiotics which may result in significant elevation of the PTINR and should be monitored by daily PTINR levels. (1)
Vitamin K affected by vitamin E intake:
Vitamin K level may be reduced by vitamin E intake. Researchers conducted a study to determine if vitamin E supplementation affects vitamin K status or blood clotting time in patients not treated with warfarin. Their study involved 38 men and women with rheumatoid arthritis and 32 healthy men participating in two independent 12-week randomized clinical trials of vitamin E supplementation. All trial participants were given 1000 IU/day of natural vitamin-E. The researchers used plasma concentration of proteins induced by vitamin K absence-factor II, or PIVKA-II for short, as a sensitive measure of vitamin K status. A normal value for PIVKA-II is 2.4 ng/mL or less and values higher than this indicate poorer vitamin-K status. At the end of the 12-week supplementation period PIVKA-II had increased from 1.7 to 11.9 ng/mL in the rheumatoid arthritis group and from 1.8 to 5.3 ng/mL in healthy men. Thus, it would appear that supplementation with a high dose of vitamin E does indeed reduce body stores of vitamin K. The researchers concluded that high-dose vitamin E supplementation does reduce vitamin K status, but are uncertain whether this interaction is immaterial, beneficial (reduced stroke risk) or harmful (loss of bone density). (2)
Vitamin K content in green tea:
Green tea extract, which contains vitamin K, may prevent clotting of the blood and thus limit the effect of warfarin. (3)
Taylor JR et al reported that a 44-year-old white male taking warfarin and one-half to one gallon of green tea per day. The PTINR went from 3.79 to 1.37 while drinking ½ to 1 gallon of green tea per day and dropped to as low as 1.14. Removal of the green tea caused normalization of his blood tests with a PTINr of 2.55. Those taking green tea and warfarin together should keep an accurate consistent intake of vitamin K containing foods to maintain therapeutic range of the INR. It was stated by the author that the concentration of the vitamin K in green tea depends on the amount of the green tea leaves brewed and the amount of green tea consumed which was a large amount in this case. Black tea leaves contain only about 18% of the amount of vitamin K found in green tea leaves. (4)
Vitamin K levels in coffee and tea:
An examination of vitamin K in brewed tea and coffee revealed that vitamin K concentrations were about 0.03 μg/100 mL or less. Therefore according to this source brewed tea or coffee contains extremely small amounts of vitamin K and is not a dietary source. (5)
Common Highest Vitamin K Containing Foods:
| Kale, frozen, cooked, boiled, drained, without salt, 1 cup | 1146.6 mcg |
| Kale, cooked, boiled, drained, without salt, 1 cup | 1062.1 mcg |
| Collards, frozen, chopped, cooked, boiled, drained, without salt, 1 cup | 1059.4 mcg |
| Spinach, frozen, chopped or leaf, cooked, boiled, drained, without salt, 1cup | 1027.3 mcg |
| Spinach, canned, regular pack, drained solids, 1 cup | 987.8 mcg |
| Spinach, cooked, boiled, drained, without salt, 1 cup | 888.5 mcg |
| Turnip greens, frozen, cooked, boiled, drained, without salt, 1 cup | 851.0 mcg |
| Mustard greens, cooked, boiled, drained, without salt, 1 cup | 829.8 mcg |
| Collards, cooked, boiled, drained, without salt, 1 cup | 772.5 mcg |
| Beet greens, cooked, boiled, drained, without salt, 1 cup | 697.0 mcg |
| Dandelion greens, cooked, boiled, drained, without salt, 1 cup | 579.0 mcg |
| Turnip greens, cooked, boiled, drained, without salt, 1 cup | 529.3 mcg |
| Brussels sprouts, frozen, cooked, boiled, drained, without salt, 1 cup | 299.9 mcg |
| Broccoli, cooked, boiled, drained, without salt, 1 cup | 220.1 mcg |
| Brussels sprouts, cooked, boiled, drained, without salt, 1 cup | 218.9 mcg |
| Onions, spring or scallions (includes tops and bulb), raw, 1 cup | 207.0 mcg |
| Spinach soufflé, 1 cup | 172.0 mcg |
| Lettuce, butterhead (includes boston and bibb types), raw, 1 head | 166.7 mcg |
| Parsley, fresh, 10 sprigs | 164.0 mcg |
| Cabbage, cooked, boiled, drained, without salt, 1 cup | 163.1 mcg |
| Broccoli, frozen, chopped, cooked, boiled, drained, without salt, 1 cup | 162.1 mcg |
| Noodles, egg, spinach, cooked, enriched, 1 cup | 161.8 mcg |
| Spinach, raw, 1 cup | 144.9 mcg |
| Asparagus, frozen, cooked, boiled, drained, without salt, 1 cup | 144.0 mcg |
| Lettuce, iceberg (includes crisphead types), raw, 1 head | 129.9 mcg |
| Endive, raw, 1 cup | 115.5 mcg |
| Broccoli, raw, 1 cup | 89.4 mcg |
| Okra, frozen, cooked, boiled, drained, without salt, 1 cup | 88.0 mcg |
| Lettuce, green leaf, raw, 1 cup | 70.7 mcg |
| Fast foods, coleslaw, 3/4 cup | 70.2 mcg |
| Plums, dried (prunes), stewed, without added sugar, 1 cup | 64.7 mcg |
Adapted from: Nutritive Value of Foods, United States Department of Agriculture, Agricultural Research Service, Home and Garden Bulletin Number 72. May be accessed at:
https://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25w430.pdf and http://www.nal.usda.gov/fnic/foodcomp/Data/HG72/hg72_2002.pdf
Assessment and Plan: Vitamin K
- Vitamin K is best known for its role in assisting blood to clot, or coagulate. Vitamin K is a fat-soluble vitamin found in a number of foods, including leafy green vegetables. Vitamin K deficiency is rare.
- In patients, taking warfarin, it is important to consume consistent amounts of vitamin K in the diet in order for the PTINR to attain and remain within stable range. Vitamin K supplements, or foods containing high amounts of vitamin K, should not be consumed with warfarin. Instead, a diet while on warfarin can include low to moderate amounts of vitamin K containing food sources as long as the same type and amount is consumed every day so that vitamin K intake remains consistently the same.
- Vitamin K levels may be reduced by the use of antibiotics, especially concerning for patient taking warfarin which may result in significant elevation of the PTINR and should be monitored by daily PTINR levels (1).
- High dose of vitamin E reduced body stores of vitamin K (2).
- For patients taking warfarin, brewed black tea or green tea in consistent small amounts (up to 2 cups per day) will not affect PTINR. However, it may be an overlooked source of vitamin K (3,4,5). If the whole ground leaves are used, vitamin K is present in much higher amounts
- The research the vitamin K content in foods, please see: Nutritive Value of Foods, United States Department of Agriculture, Agricultural Research Service, Home and Garden Bulletin Number 72. May be accessed at: https://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25w430.pdf
References:
1.Jones CB, Fugate SE. Levofloxacin and warfarin interaction. Ann Pharmacother. 2002 Oct;36(10):1554-7. http://www.ncbi.nlm.nih.gov/pubmed/12243605
2.Booth SL, Golly I, Sacheck JM, Roubenoff R, Dallal GE, Hamada K, Blumberg JB. Effect of vitamin E supplementation on vitamin K status in adults with normal coagulation status. Am J Clin Nutr. 2004 Jul;80(1):143-8. http://www.ncbi.nlm.nih.gov/pubmed/15213041
3.Agency for Healthcare Research and Quality. Comparative Effectiveness of Dietary Supplement Versus No Dietary Supplement Use in Adults Taking Cardiovascular Drugs. April 2012. http://www.effectivehealthcare.ahrq.gov/ehc/products/223/596/DietarySupplement_Amended_Protocol_20110428.pdf
4.Taylor JR, Wilt VM. Probable antagonism of warfarin by green tea. Ann Pharmacother. 1999 Apr;33(4):426-8. http://www.ncbi.nlm.nih.gov/pubmed?term=10332534
5.Booth SL, Madabushi HT, Davidson KW, Sadowski JA. Tea and coffee brews are not dietary sources of vitamin K-1 (phylloquinone). J Am Diet Assoc. 1995 Jan;95(1):82-3. http://www.ncbi.nlm.nih.gov/pubmed/7798585
6.Nutritive Value of Foods, United States Department of Agriculture, Agricultural Research Service, Home and Garden Bulletin Number 72. May be accessed at: https://www.ars.usda.gov/SP2UserFiles/Place/12354500/Data/SR25/nutrlist/sr25w430.pdf