Vitamin D3 is one of the most supplemented nutrients in the UK, and for good reason: deficiency is widespread, the consequences for immune function, bone health, and mood are well documented, and supplementation is safe and inexpensive. What is less commonly understood is the relationship between vitamin D3 and vitamin K2, a nutrient that regulates where calcium goes once vitamin D has ensured it is absorbed. Without adequate K2, the increased calcium uptake driven by D3 supplementation has no molecular direction, and calcium may accumulate in soft tissues, blood vessel walls, and kidneys rather than bone.
Vitamin K2 and Calcium Trafficking
Vitamin K2 activates two calcium-binding proteins through a process called carboxylation. Osteocalcin, produced by osteoblasts, is carboxylated by K2 and then binds calcium ions within the bone matrix, anchoring calcium in bone. Matrix Gla-protein, present in arterial walls and soft tissues, is also K2-dependent and, when activated, prevents calcium deposition in vascular tissue. Deficiency of K2 leaves osteocalcin and matrix Gla-protein in their inactive, undercarboxylated form, impairing bone mineralisation and leaving arterial calcium unchecked. Arterial calcification is a significant and independent cardiovascular risk factor.
The Rotterdam Study
The Rotterdam Study, a large population cohort study in the Netherlands, found that dietary vitamin K2 intake was inversely associated with coronary calcification, aortic calcification, and cardiovascular mortality. Participants in the highest tertile of K2 intake had 57 percent lower risk of dying from heart disease compared to those in the lowest tertile. Dietary vitamin K1, the form found in leafy greens, showed no significant association. The specific K2 form associated with the strongest cardiovascular benefit was MK-7, which has the longest half-life and best tissue distribution of all K2 forms.
Supplementing D3 and K2 Together
The most practical approach for most adults supplementing D3 is to use a combined D3 and K2 preparation or to take them simultaneously. The K2 form MK-7, derived from natto or synthetic sources, is preferable to MK-4 due to its longer half-life and better evidence base. Doses studied in clinical trials range from 90 to 360 micrograms of MK-7 daily. Adults taking anticoagulant medications, particularly warfarin, should consult their prescriber before adding K2 as it may affect coagulation monitoring.
- Take D3 and K2 MK-7 together, either as a combined supplement or simultaneously
- Target 90 to 180 micrograms of K2 MK-7 daily alongside 1000 to 2000 IU of D3
- Take with a meal containing fat: both D3 and K2 are fat-soluble and absorption is substantially improved with dietary fat
- If you take warfarin, consult your anticoagulation clinic before starting K2
- Natto, a Japanese fermented soya product, is the richest dietary source of MK-7 at approximately 1000 micrograms per 100g
Sources
- Geleijnse, J.M., et al. (2004). Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease. Journal of Nutrition, 134(11), 3100-3105.
- Schurgers, L.J., & Vermeer, C. (2001). Determination of phylloquinone and menaquinones in food. Haemostasis, 30(6), 298-307.