At this very moment, your bloodstream contains a protein that was produced but never fully activated.
That protein is osteocalcin.
It is released by bone-forming cells and is responsible for binding calcium and incorporating it into the bone matrix. However, when osteocalcin is first made, it is inactive. Before it can perform its function, it must undergo a process called carboxylation, which depends entirely on vitamin K.
When vitamin K levels are insufficient, osteocalcin remains in its inactive form, known as undercarboxylated osteocalcin (ucOC). It continues to circulate through the bloodstream. It is detectable, abundant, but unable to effectively support bone mineralization.
This unfinished protein is one of the most overlooked pieces of the conversation about bone health during menopause.
Why menopause changes the arithmetic?
As estrogen levels decline during menopause, the balance between bone formation and bone resorption begins to shift. Bone is broken down faster than it can be rebuilt, accelerating bone loss (Zhang et al., 2025).
The usual advice at this stage is to increase calcium and vitamin D intake. Both are essential because they ensure the body has the raw materials needed to maintain healthy bones.
Vitamin K2, however, plays a different role. Rather than supplying calcium, it directs where that calcium goes. According to Kim et al. (2024), vitamin K2 activates two key proteins through carboxylation: osteocalcin, which binds calcium and incorporates it into bone tissue, and matrix Gla protein (MGP), which helps prevent calcium from accumulating in the walls of arteries. In other words, while calcium provides the building blocks, vitamin K2 helps ensure they end up in the right place, strengthening bones instead of contributing to vascular calcification.
What the trials actually found (including where they disagree)
Clinical evidence on vitamin K2 and bone health in postmenopausal women has produced mixed findings, with some studies demonstrating structural benefits while others report little effect on bone mineral density.
Knapen et al. (2013) gave 244 healthy postmenopausal women 180 µg of MK-7 daily for three years. The supplemented group showed a significantly slower age-related decline in bone mineral density at the lumbar spine and femoral neck, better bone strength indices, and less loss of vertebral height in the lower thoracic spine. Total hip showed no difference.
Then a Danish team ran a harder test. Ronn et al. (2021) gave 142 postmenopausal women with osteopenia 375 µg of MK-7 daily for three years, on top of calcium and vitamin D. Undercarboxylated osteocalcin fell by roughly 65%. Bone mineral density declined at a rate similar to the placebo group, with no significant differences in bone turnover markers or bone microarchitecture.
Interestingly, an earlier 12-month analysis from the same research group had reported more encouraging results. Women receiving MK-7 maintained trabecular number, spacing, and thickness at the tibia, whereas the placebo group exhibited the gradual deterioration typically associated with age-related bone loss (Ronn et al., 2016). These findings suggested that vitamin K2 might initially preserve bone microstructure, although these effects were not sustained over the longer follow-up period.
Evidence from systematic reviews and meta-analyses offers a more balanced perspective. Ma et al. (2022), in a meta-analysis of 16 randomized controlled trials involving 6,425 women, reported a significant improvement in lumbar spine bone mineral density following vitamin K2 supplementation (p = 0.006). While the overall reduction in fracture risk was not statistically significant, excluding one heterogeneous trial lowered the pooled risk ratio to 0.43, indicating a potential protective effect. Similarly, Zhang et al. (2025), who analyzed data from nine randomized trials involving 2,570 participants, found that vitamin K2 consistently improved biochemical markers of bone metabolism. Supplementation increased osteocalcin and bone-specific alkaline phosphatase levels while significantly reducing undercarboxylated osteocalcin, demonstrating reliable activation of vitamin K-dependent pathways, even when measurable improvements in bone density were less consistent.
K2 consistently changes the chemistry. Whether that shows up on a DXA scan appears to depend on who is being studied, healthy women earlier in the transition responded; women already osteopenic and already supplemented did not.
Not all vitamin K is same
Although vitamin K is often discussed as a single nutrient, its different forms do not behave the same way in the body. Evidence suggests that the specific form of vitamin K, particularly MK-4 versus MK-7 can have a substantial impact on its bioavailability.
Sato et al. (2012) compared these two forms by administering a single 420 µg dose of either MK-4 or MK-7 to healthy women. MK-7 reached peak serum concentrations approximately six hours after ingestion and remained detectable for up to 48 hours. In contrast, MK-4 could not be detected in the blood at any time point. During a subsequent seven-day supplementation period with 60 µg daily, serum MK-7 levels increased consistently in every participant, whereas MK-4 again produced no measurable rise.
These findings indicate that the term “vitamin K2” alone provides limited information. The physiological effects of supplementation depend not only on the dose but also on the specific menaquinone form being consumed.
Recommended Intake and Dietary Sources
The European Food Safety Authority (EFSA, 2017) recommends an adequate intake of 70 µg of vitamin K per day for adults. This recommendation is based on phylloquinone (vitamin K1), as no separate dietary reference value has yet been established for vitamin K2.
Natural dietary sources of vitamin K2 are relatively limited. Foods such as natto (fermented soybeans), aged cheeses, egg yolks, and organ meats provide meaningful amounts, but these are consumed infrequently in many Western dietary patterns. Consequently, habitual vitamin K2 intake tends to be low in these populations (Kim et al., 2024).
An important clinical consideration is the interaction between vitamin K and warfarin, an anticoagulant whose effectiveness depends on vitamin K metabolism. Because supplemental vitamin K can interfere with warfarin therapy, individuals taking this medication should consult their healthcare provider before starting any vitamin K supplement.
Where TerraQuino comes in
TerraQuino produces an allergen-free Vitamin K2-7 (MK-7) ingredient through a controlled fermentation process, supplying nutraceutical brands rather than consumers directly. The focus is on the variables i.e. the long-chain MK-7 form, stability, and bioavailability across formats including tablets, capsules, soft gels, sachets and liquids.
For a formulator, that means the finished product delivers the form the trials actually tested. For a shopper, it means the sensible question at the shelf is which menaquinone is in there and at what dose.
Frequently asked questions
Does vitamin K2 replace calcium or vitamin D?
No. They do different jobs. Calcium is raw material, vitamin D helps you absorb it, and K2 activates the proteins that decide where it ends up. In the Ronn et al. (2021) trial, K2 was tested as an add-on to calcium and vitamin D, not as a substitute.
MK-4 or MK-7 — does the difference matter?
Measurably. In Sato et al. (2012), nutritional doses of MK-4 never reached detectable serum levels, while MK-7 did in every participant and stayed detectable for two days.
How long before anything changes?
Blood markers move fast; undercarboxylated osteocalcin dropped within three months in Ronn et al. (2016). Bone density is slower; the trials that measured it ran for three years.
Can I get enough vitamin K2 from food?
Possible if you eat natto regularly. Difficult otherwise, which is the reason Kim et al. (2024) argue for supplementation alongside diet in Western populations.
Is the evidence settled?
Not yet. The biochemical effect is consistent across trials; the bone density effect is not. Zhang et al. (2025) call explicitly for longer studies before claiming clinical benefit. That uncertainty is worth knowing before you buy anything.
References
European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies. (2017). Dietary reference values for vitamin K. EFSA Journal, 15(5), e04780. https://doi.org/10.2903/j.efsa.2017.4780
Kim, T.-H., Kim, H., Lee, H. H., & Sang, J. H. (2024). Vitamin K: Calcium metabolism modulator for menopausal women. Journal of Menopausal Medicine, 30(3), 152–163. https://doi.org/10.6118/jmm.24023
Knapen, M. H. J., Drummen, N. E., Smit, E., Vermeer, C., & Theuwissen, E. (2013). Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporosis International, 24(9), 2499–2507. https://doi.org/10.1007/s00198-013-2325-6
Ma, M.-L., Ma, Z.-J., He, Y.-L., Sun, H., Yang, B., Ruan, B.-J., Zhan, W.-D., Li, S.-X., Dong, H., & Wang, Y.-X. (2022). Efficacy of vitamin K2 in the prevention and treatment of postmenopausal osteoporosis: A systematic review and meta-analysis of randomized controlled trials. Frontiers in Public Health, 10, 979649. https://doi.org/10.3389/fpubh.2022.979649
Rønn, S. H., Harsløf, T., Pedersen, S. B., & Langdahl, B. L. (2016). Vitamin K2 (menaquinone-7) prevents age-related deterioration of trabecular bone microarchitecture at the tibia in postmenopausal women. European Journal of Endocrinology, 175(6), 541–549. https://doi.org/10.1530/EJE-16-0498
Rønn, S. H., Harsløf, T., Oei, L., Pedersen, S. B., & Langdahl, B. L. (2021). The effect of vitamin MK-7 on bone mineral density and microarchitecture in postmenopausal women with osteopenia, a 3-year randomized, placebo-controlled clinical trial. Osteoporosis International, 32(1), 185–191. https://doi.org/10.1007/s00198-020-05638-z
Sato, T., Schurgers, L. J., & Uenishi, K. (2012). Comparison of menaquinone-4 and menaquinone-7 bioavailability in healthy women. Nutrition Journal, 11, 93. https://doi.org/10.1186/1475-2891-11-93
Zhang, Z., Li, Y., Li, J., Yuan, Y., Liu, K., & Shi, X. (2025). The effect of vitamin K2 supplementation on bone turnover biochemical markers in postmenopausal osteoporosis patients: A systematic review and meta-analysis. Frontiers in Endocrinology, 16, 1703116. https://doi.org/10.3389/fendo.2025.1703116
