Effects of Vitamin K on Medication and Bone Health

Vitamin K is the name of a group of common chemical structures, including: phylloquinone (vitamin K1), menaquinones (vitamin K2) and menadione (vitamin K3). Vitamin K1 is common in leafy green and other vegetables, whereas K2, which is derived primarily from bacteria, is present in large amounts in the fermented soy product natto and in modest amounts in meat and cheese. Vitamin K3 is a synthetic form that may be added to animal feed.

Certain medications and supplements have the potential to interact with any form of vitamin K. For example, the anticoagulant medication warfarin decreases the activity of vitamin K which plays an essential role in the formation of blood clots. Alternatively, an unanticipated increase in vitamin K could decrease the effectiveness of warfarin for those who have been prescribed a specific dose by their medical provider.

For patients on warfarin, current vitamin K nutrition therapy recommendations include keeping intake of vitamin K-rich foods consistent so the effect on coagulation time is as constant and predictable as possible. However, some individuals are advised or choose to avoid vitamin-K rich foods to regulate their intake and keep it consistent. A 2016 study published in the Journal of the Academy of Nutrition and Dietetics suggests that lower than usual intake of vitamin K is common among warfarin users due to the avoidance of green vegetables and other vitamin K-rich foods.

As vitamin K research has evolved over the years, it has led to the discovery of vitamin K-dependent reactions beyond coagulation, including proteins involved in bone metabolism. Vitamin K plays a role as a coenzyme during the synthesis of osteocalcin, a protein derived from osteoblasts involved in bone formation. A study involving natto, a traditional Japanese food made from steamed, fermented, and mashed soybeans, suggested that regular consumption of natto was associated with significantly higher bone mineral density among older Japanese men. Additionally, the study found BMD to be higher both at the femoral neck and total hip, suggesting a possibility for reduced hip-fracture risk among this population with regular natto intake.

Another excellent source of vitamin K are dried plums, also known as prunes, which may be more commonly associated with digestive health. However, during the 2022 World Congress on Osteoporosis, Osteoarthritis, and Musculoskeletal Diseases, results from a randomized, controlled trial were presented demonstrating that participants who were all postmenopausal maintained their hip BMD over a year's time by ingesting 50 grams, or the equivalent of 5 to 6, dried plums daily; whereas, BMD decreased at six and twelve months in the control group.

In comparison, a 2019 systematic review and meta-analysis found little evidence to support the role of supplemental vitamin K in improving BMD or vertebral fractures among individuals who were postmenopausal or diagnosed with osteoporosis. Although the studies reviewed indicated a possible reduction of fractures seen in a clinical setting.

While advances in research on bone health are promising, the exact mechanisms for preserving BMD remain elusive and could be a result of the synergy between several nutrients. In the meantime, obtaining this fat soluble vitamin and other important nutrients from dietary sources, remains a recommended and important part of a healthy eating plan. Registered dietitian nutritionists can assist individuals who may need to modify their intake of vitamin K in order to achieve adequate amounts and in alignment with their treatment goals.

References:

• National Institutes of Health. Office of Dietary Supplements. Vitamin K: Fact Sheet for Health Professionals. Accessed April 8, 2022.
• Leblanc C, Dubé M-P, Presse N, et al. Avoidance of vitamin K_rich foods is common among warfarin users and translates into lower usual vitamin K intakes. J Acad Nutr Diet. 2016;116(6):1000-1007.
• Fujita Y, Iki M, Tamki J, et al. Association Between Vitamin K Intake From Fermented Soybeans, Natto, and Bone Mineral Density in Elderly Japanese Men: The Fujiwara-kyo Osteoporosis Risk in Men (FORMEN) Study. Osteoporos Int. 2012; 23(2):705-14.
• De Souza, M.J. (2022, March 24-26). Prunes preserve hip bone mineral density and FRAX risk in a 12-month randomized controlled trial in postmenopausal women: The Prune Study [Abstract presentation]. World Congress on Osteoporosis, Osteoarthritis and Musculoskeletal Diseases, online. https://virtual.wco-iof-esceo.org/
• Mott A, Bradley T, Wright K. Effect of Vitamin K on Bone Mineral Density and Fractures in Adults: An Updated Systematic Review and Meta-Analysis of Randomised Controlled Trials. Osteoporos Int. 2019; 30(8):1543-1559.