Someone once asked me why I recommend taking Vitamin D3 with K2? Truth be told, I was told in one of my clinical nutrition lectures that the two work better together synergistically. Anecdotally, I have been taking this combination and have been able to successful raise my vitamin D to about 80ng/ml. But I have not really done formal research in their benefits taken together. The point of this blog is to review them to see what the hype is all about.
Vitamins D and K are both fat-soluble vitamins and play a central role in calcium metabolism, and optimal concentrations of both vitamins are beneficial for both bone and cardiovascular health (van Ballegooijen, Pilz, Tomaschitz, Grubler, & Verheyen, 2017). Vitamin D is a fat-soluble vitamin that can be ingested by foods such as fatty fish, dairy products, and eggs, but is mainly synthesized by the human skin when exposed to sunlight (van Ballegooijen et al., 2017). Vitamin D plays a main role in regulating calcium metabolism by increasing intestinal calcium absorption. Vitamin K is another fat-soluble vitamin that exists in two forms of vitamin K: vitamin K1 (phylloquinone, mainly found in green leafy vegetables, role is to regulate coagulation factors) and vitamin K2 (menaquinone, mainly found in fermented dairy and produced by lactic acid bacteria in the intestine, regulating proteins involved in bone maintenance) (van Ballegooijen et al., 2017). “The current recommendation for vitamin K1 intake is 70 μg/day for all adults defined by an adequate intake (van Ballegooijen et al., 2017). (Interesting according to van Ballegooijen et al, this amount is solely based on maintaining coagulation function and might not be enough for optimal carboxylation of other vitamin K-dependent proteins, which require higher amounts of vitamin K).
So here are some of the ways vitamin D and K2 can work synergistically together:
- Bone Health-Vitamin D supplementation may stimulate intestinal calcium absorption with prevention of the abnormal elevation of serum PTH concentrations, preventing hypocalcemia. “Taken together the evidence for combined vitamin D and K supplementation, the majority of the studies found beneficial effects for BMD among postmenopausal women” (van Ballegooijen et al., 2017).
- Cardiovascular Health-low vitamin D levels and uncarboxylated MGP (due to low vitamin K) can increase the risk of hypertension compared to subjects with low vitamin D and normal MGP carboxylation suggesting that vitamin K may have a role in regulating hypertension (Vitamin Council, n.d.). Also researchers discovered that vitamin K supplementation in conjunction to vitamin D supplementation reduced the progression of atherosclerosis in patients with chronic kidney disease (CKD) significantly more so than supplementing with vitamin D alone (Vitamin Council, n.d.).
- Glucose metabolism and inflammation-The joint supplementation of vitamins D and K might improve insulin metabolism through an effect on upregulation of the insulin receptor genes, the regulation of insulin secretion from the pancreatic beta-cell, the enhancement of β-cell proliferation, and suppression of parathyroid hormone (van Ballegooijen et al., 2017). Vitamins D and K has also shown to have beneficial effects on endocrine and oxidative stress markers.
Other interesting facts about vitamin K. Vitamin K is carried in lipoprotein and very small amounts circulate in the blood, as it is rapidly metabolized and excreted. The body only retains about 30-40% of oral physiological dose. Research indicates that substantial quantities of long-chain menaquinones are present in the large bowel. Antibiotics can destroy vitamin K-producing bacteria in the gut, potentially decreasing vitamin K status (NIH, n.d.). This effect might be more pronounced with cephalosporin antibiotics because these antibiotics might also inhibit the action of vitamin K in the body (NIH, n.d.).
A subsequent clinical trial found that MK-7 supplementation (180 mcg/day for 3 years) improved bone strength and decreased the loss in vertebral height in the lower thoracic region of the vertebrae in postmenopausal women (NIH, n.d.). But in general, the studies are conflicting to date. The most widely used vitamin K form for supplementation is vitamin K2 and more specifically menaquinone-4 and menaquinone-7. Menaquinone-7 has a higher bioavailability and may be of particular importance for extrahepatic tissue. The table provided by the NIH gives a nice list of different foods and their vitamin K content, with collards, natto, turnip greens, kale and spinach listed at the top.
National Institute of Health. (n.d.) Vitamin K. Retrieved (2018, March 23) from https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/
van Ballegooijen, A. J., Pilz, S., Tomaschitz, A., Grubler, M. R., & Verheyen, N. (2017). The Synergistic Interplay between Vitamins D and K for Bone and Cardiovascular Health: A Narrative Review. Int J Endocrinol, 2017, 7454376. doi:10.1155/2017/7454376
Vitamin Council (n.d.) The synergistic relationship between vitamin D and vitamin K. Retrieved (2018, March 23) from https://www.vitamindcouncil.org/the-synergistic-relationship-between-vitamin-d-and-vitamin-k/