Vitamin K2 and Bone Density: What Your DEXA Scan Reveals About the Overlooked Nutrient in Bone Health

You take calcium. You take vitamin D. Your GP has checked your levels and everything looks fine. Yet your DEXA scan still shows bone mineral density lower than expected, or a T-score that has barely shifted after a year of supplementation. What might be missing?

The answer could be vitamin K2. While calcium provides the raw building material for bone and vitamin D helps you absorb it from your gut, vitamin K2 plays a different and equally critical role: it activates the proteins that direct calcium into bone tissue and keep it out of your arteries. Without adequate K2, calcium can end up in the wrong places, leaving bones under-mineralised and soft tissue at risk of calcification.

Despite growing evidence from systematic reviews and clinical trials, vitamin K2 remains one of the most overlooked nutrients in UK bone health practice. This article explains what K2 does at the molecular level, what the research says about its effect on bone mineral density, and how a bone density DEXA scan can track whether optimising your K2 intake is making a measurable difference.

Vitamin K exists in two main forms. Vitamin K1 (phylloquinone) is found in leafy green vegetables and is primarily involved in blood clotting. Vitamin K2 (menaquinone) is a group of related compounds, found in fermented foods and certain animal products, that plays a distinct role in calcium metabolism and bone mineralisation.

The two most studied forms of K2 are MK-4 (menaquinone-4), a short-chain variant found in egg yolks, liver, and dark poultry meat, and MK-7 (menaquinone-7), a long-chain variant produced by bacterial fermentation and found in high concentrations in natto, a traditional Japanese fermented soybean dish.

While K1 is relatively abundant in a balanced diet, K2 is far harder to obtain in meaningful amounts from typical Western eating patterns. This matters because K2 has a specific function that K1 cannot fully replicate: it activates the proteins responsible for depositing calcium into bone and preventing its accumulation in blood vessels.

The mechanism behind K2’s role in bone health centres on a process called gamma-carboxylation. Two proteins in particular depend on vitamin K2 for activation.

The first is osteocalcin, a protein produced by osteoblasts (bone-building cells). In its inactive, undercarboxylated form, osteocalcin cannot bind calcium effectively. Vitamin K2 converts it into its active, carboxylated form, which then binds calcium ions and incorporates them into the hydroxyapatite crystal lattice that gives bone its strength and density. Research published in the Journal of Bone and Mineral Metabolism has confirmed that higher levels of undercarboxylated osteocalcin in the blood are associated with lower bone mineral density and increased fracture risk (Tsugawa et al., 2008).

The second is matrix Gla-protein (MGP), which inhibits calcium deposition in soft tissues, including arterial walls. When MGP remains undercarboxylated due to insufficient K2, calcium that should be going to bone can instead accumulate in arteries. This dual role makes K2 relevant not only to skeletal health but also to cardiovascular risk, a connection explored in the Rotterdam Study, which followed over 4,800 participants for more than seven years (Geleijnse et al., 2004).

In practical terms, taking calcium and vitamin D without adequate K2 may increase calcium absorption from the gut but leave the body less able to direct that calcium where it is needed most.

Both MK-4 and MK-7 activate osteocalcin and matrix Gla-protein, but they differ in dosing, half-life, and the depth of clinical evidence behind them.

MK-4 (menatetrenone) has been used therapeutically in Japan since 1995 as an approved treatment for osteoporosis, typically at a dose of 45 mg per day. At this pharmacological dose, clinical trials have demonstrated reductions in vertebral, hip, and non-vertebral fractures in postmenopausal women. However, MK-4 has a short half-life of around one to two hours, which means it requires multiple daily doses to maintain effective blood levels.

MK-7 has a considerably longer half-life of approximately 72 hours, allowing once-daily dosing at much lower amounts, typically 100 to 200 micrograms. A three-year randomised controlled trial published in Osteoporosis International found that 180 micrograms of MK-7 daily significantly reduced the age-related decline in bone mineral density at the lumbar spine and femoral neck in healthy postmenopausal women, compared with placebo (Knapen et al., 2013).

For most people considering supplementation in the UK, MK-7 is the more practical option due to its longer duration of action, lower dosing requirements, and wider availability in over-the-counter supplements. MK-4 at therapeutic doses requires clinical supervision and is not routinely available outside Japan and parts of Asia.

A 2022 systematic review and meta-analysis published in Frontiers in Public Health, which pooled data from multiple randomised controlled trials, found that vitamin K2 supplementation significantly improved bone mineral density at the lumbar spine in postmenopausal women (Ma et al., 2022). The same review noted a meaningful reduction in fracture incidence among supplemented groups.

An earlier meta-analysis in the Archives of Internal Medicine examined 13 randomised trials and concluded that vitamin K2 reduced vertebral fractures by approximately 60%, hip fractures by approximately 77%, and all non-vertebral fractures by approximately 81% (Cockayne et al., 2006). Most of these trials used MK-4 at the 45 mg therapeutic dose used in Japan.

It is important to note that results across studies are not perfectly uniform. A 2025 review published in Contemporary OB/GYN described the overall evidence as “mixed,” observing that while high-dose MK-4 trials in Japanese populations consistently showed benefit, lower-dose MK-7 trials in Western populations have produced more variable results for fracture endpoints specifically. Bone mineral density improvements, however, were more consistently observed across both forms.

What the evidence consistently supports is that K2 reduces levels of undercarboxylated osteocalcin and improves markers of bone turnover, even when the effect on DEXA-measured bone density takes time to reach statistical significance. This aligns with how bone remodelling works: changes in bone formation markers often precede detectable changes in bone mineral density by 6 to 12 months.

The richest dietary source of vitamin K2 by a wide margin is natto, the Japanese fermented soybean dish, which contains roughly 1,000 micrograms of MK-7 per 100-gram serving. Outside of natto, meaningful K2 intake becomes considerably harder to achieve through diet alone.

Other food sources include aged hard cheeses such as Gouda and Emmental (which provide MK-8 and MK-9 in moderate amounts), egg yolks, liver, dark chicken meat, and butter from grass-fed animals. Fermented vegetables like sauerkraut contain small amounts of MK-7, though far less than natto.

There is no official UK recommended daily intake for vitamin K2 specifically. The NHS recommends approximately 1 microgram of vitamin K per kilogram of body weight per day, but this refers to total vitamin K (primarily K1 for clotting function) rather than K2 for bone and vascular health. Based on the clinical trial evidence, most researchers and supplementation guidelines suggest 100 to 200 micrograms of MK-7 daily for bone health support, or 45 mg of MK-4 daily under clinical supervision for therapeutic use.

Important note for patients on anticoagulants: vitamin K2, like vitamin K1, can interact with warfarin and other vitamin K antagonist anticoagulants. If you take warfarin, you should consult your doctor before starting any vitamin K2 supplement. Newer anticoagulants such as apixaban, rivaroxaban, and edoxaban (DOACs) do not interact with vitamin K in the same way, but medical advice before supplementation is always prudent.

Vitamin D, calcium, and vitamin K2 each address a different step in the process of building and maintaining bone. Calcium is the mineral that forms bone’s structural framework. Vitamin D increases calcium absorption from the gut, which is why deficiency leads to poor mineralisation regardless of how much calcium you consume. Vitamin K2 then activates the proteins that incorporate that absorbed calcium into bone tissue.

When any one of these three nutrients is missing, the others cannot fully compensate. A person with adequate calcium and vitamin D but insufficient K2 may absorb calcium well but deposit it poorly, leading to suboptimal bone mineralisation and, in some cases, arterial calcification. This is one reason why some studies have raised concerns about high-dose calcium supplementation without concurrent attention to K2 status.

If you have already read our guides on vitamin D and bone density, calcium and bone density, and how magnesium affects bone density and osteoporosis risk, adding K2 to the picture completes the full nutrient strategy for skeletal health. All three nutrients work best in concert, and a DEXA scan performed at 12 to 24 month intervals is the most reliable way to confirm that the combination is producing measurable results in your bone mineral density.

A DEXA (dual-energy X-ray absorptiometry) scan measures bone mineral density at key skeletal sites, typically the lumbar spine, femoral neck, and total hip. It produces a T-score that compares your bone density to that of a healthy 30-year-old adult, and a Z-score that compares it to others of your age and sex.

For someone who has optimised their vitamin K2 intake alongside vitamin D and calcium, a follow-up DEXA scan after 12 to 24 months can reveal whether bone mineral density has stabilised, improved, or continued to decline. This is particularly valuable for postmenopausal women, individuals with osteopenia, and anyone whose initial scan showed accelerated bone loss relative to their age.

It is worth noting that bone remodelling is a slow process. A single cycle of bone resorption and formation takes approximately four to six months, so meaningful changes in DEXA-measured density typically require at least a year to become detectable. This is why your clinician will normally recommend a repeat scan at 12 to 24 month intervals rather than every few months.

What a DEXA scan cannot tell you is your vitamin K2 status directly. Blood tests for undercarboxylated osteocalcin (ucOC) can provide an indirect marker of K2 sufficiency, and some clinicians use this alongside DEXA results to build a more complete picture of bone turnover and nutrient status.

Can I get enough vitamin K2 from diet alone?
It depends on your dietary pattern. If you regularly eat natto, aged hard cheeses, and egg yolks, you may obtain meaningful amounts of K2. However, most Western diets provide well under 50 micrograms of K2 per day, which is below the levels shown to benefit bone density in clinical trials. For many people, supplementation with MK-7 at 100 to 200 micrograms daily is a practical option.

Is vitamin K2 safe if I take blood thinners?
If you take warfarin or another vitamin K antagonist, you should not start K2 supplementation without consulting your prescribing doctor, as K2 can reduce the drug’s effectiveness. If you take a direct oral anticoagulant (DOAC) such as apixaban or rivaroxaban, the interaction risk is much lower, but medical advice before supplementation is still recommended.

Should I take vitamin K2 with vitamin D?
There is strong biological rationale for combining K2 with vitamin D. Vitamin D increases calcium absorption and stimulates osteocalcin production, while K2 activates that osteocalcin so it can bind calcium into bone. Taking one without the other may limit the overall benefit to your bones.

How soon will a DEXA scan show the effect of K2 supplementation?
Bone remodelling is slow. Most clinicians recommend waiting at least 12 months before a follow-up DEXA scan to assess the impact of any nutritional or pharmacological intervention. Blood markers of bone turnover may change sooner, but measurable bone density shifts typically require one to two years.

Is MK-7 or MK-4 better for bone health?
Both forms activate the same bone-building proteins. MK-4 at high therapeutic doses (45 mg/day) has the strongest fracture-reduction evidence, but it requires multiple daily doses and clinical supervision. MK-7 at 100 to 200 micrograms daily offers a longer half-life and practical once-daily dosing, with good evidence for improving bone mineral density markers. For most people in the UK, MK-7 is the more accessible choice.

If you are concerned about your bone health, or if you have already started supplementing with vitamin K2, vitamin D, and calcium and want to know whether your bones are responding, a DEXA scan provides the objective measurement you need. At DEXA London, our Harley Street clinic offers comprehensive bone density and body composition DEXA scans with detailed clinical reporting.

To book your scan or discuss whether a bone density assessment is right for you, call us on 0207 637 8227 or book online through our website. Your scan results will give you a clear, evidence-based picture of where your bone health stands today and a baseline against which to measure future progress.