If you have been told you have thinning bones, you have probably been offered calcium and vitamin D. This post looks at a third nutrient, vitamin K2 (MK-7), and what the research says.
The current standard: calcium and vitamin D
Calcium and vitamin D combinations are the cornerstone of NHS bone health prescribing. Common options include Calci-D® (1,000 mg calcium + 1,000 IU vitamin D3, once a day) and Adcal-D3® (600 mg calcium + 400 IU vitamin D3 per chewable tablet, usually twice a day) (North East London Pharmacy and Medicines Optimisation Team, 2023; NHS Highland, 2026). Both help build bone and tackle low vitamin D, which is common in UK adults in autumn and winter.
For people with osteopenia (bones thinner than normal) or osteoporosis, UK guidance supports vitamin D at 800 to 2,000 IU a day (Gregson et al., 2025). The NHS advises adults not to take more than 4,000 IU (100 micrograms) a day (NHS, n.d.).
The missing link: vitamin K2 (MK-7)
Calcium and vitamin D get calcium into your body, but neither decides where it ends up. Researchers are interested in vitamin K2's role in steering calcium into bone and away from soft tissues such as blood vessels (Wasilewski, Vervloet and Schurgers, 2019).
Vitamin K2 switches on two key proteins:
- Osteocalcin: helps bind calcium into bone.
- Matrix Gla protein (MGP): may help stop calcium building up in artery walls.
Key insight
The European Food Safety Authority (EFSA) has accepted that vitamin K contributes to the maintenance of normal bone (EFSA, 2009).
What the research says
- Bone density: a three-year trial found 180 micrograms a day of MK-7 slowed age-related bone loss in healthy women after the menopause (Knapen et al., 2013). A 2024 review found vitamin K supplements increased bone density in the lower spine, with the strongest effects in women (Xie et al., 2024).
- Bone structure: a 12-month trial found MK-7 helped protect the inner, honeycomb-like structure of the shin bone in women with osteopenia after the menopause (Rønn et al., 2016).
- Blood vessels: a three-year trial found MK-7 reduced artery stiffness (Knapen et al., 2015). A 2023 review of 14 trials found vitamin K slowed calcium build-up in the heart's arteries, though only just reaching statistical significance (Li, Wang and Tu, 2023). Another trial found no benefit for calcium build-up in the heart valve in men with aortic valve calcification (Diederichsen et al., 2022). The heart and blood vessel evidence remains mixed.
What current UK guidelines say
The 2024 UK clinical guideline from the National Osteoporosis Guideline Group (NOGG) is the main UK standard for treating osteoporosis (Gregson et al., 2025). It recommends:
- at least 700 mg calcium a day, ideally from food
- at least 800 IU vitamin D a day for people with, or at risk of, low vitamin D
- fracture risk checks using tools such as FRAX® or QFracture®
- bone-strengthening medicines, such as bisphosphonates or denosumab, as the main treatment where needed.
In 2026, NICE published a new guideline on osteoporosis risk assessment (NICE, 2026), and its Clinical Knowledge Summary gives GPs practical guidance on prevention (NICE, n.d.).
Current position
Vitamin K2 (MK-7) is not currently included in NICE or NOGG recommendations. The evidence, while promising for bone density, is not yet seen as strong enough for routine use in UK practice.
What the Royal Osteoporosis Society says
The Royal Osteoporosis Society (ROS) says diets rich in vitamin K are linked to a lower risk of hip fractures in older people. However, it states: "Evidence on the effects of vitamin K supplements on bone health and strength isn't strong, so currently supplements are not recommended" (Royal Osteoporosis Society, 2021).
Since then, the Xie et al. (2024) review has added to earlier evidence, including a 2015 analysis of 19 trials (Huang et al., 2015). This may justify a fresh look.
⚠️ Taking warfarin?
Vitamin K plays a part in blood clotting. If you take warfarin, the ROS advises that you should not take a vitamin K supplement or make big changes to your diet without talking to your GP first (Royal Osteoporosis Society, 2021).
How much is safe?
| Nutrient | Recommended intake | Upper safe limit | Notes |
|---|---|---|---|
| Calcium | At least 700 mg a day (all sources) | 2,500 mg a day (EFSA) | Food first; supplements mainly if diet is low |
| Vitamin D3 | 400 IU a day for most adults; 800 to 2,000 IU for higher-risk groups | 4,000 IU a day (NHS) | D3 preferred; daily dosing preferred |
| Vitamin K2 (MK-7) | 180 micrograms a day (dose used in trials) | No upper limit set (EFSA) | ⚠️ Not suitable with warfarin unless your GP agrees |
| Magnesium | 270 to 300 mg a day (UK reference intake) | 250 mg a day from supplements (EFSA) | Too much can cause diarrhoea; food first |
Sources: EFSA (2006); Gregson et al. (2025); NHS (n.d.); Royal Osteoporosis Society (n.d.).
A practical way forward
For people with osteopenia or osteoporosis and several risk factors, a joined-up approach could include:
- an NHS-approved calcium and vitamin D product, such as Calci-D® or Adcal-D3®
- asking your GP about vitamin K2 (MK-7), 180 micrograms a day, an affordable over-the-counter supplement
- regular checks of your vitamin D and calcium levels.
Always speak to your GP or pharmacist before starting any new supplement, especially if you take warfarin or another blood thinner, have kidney disease, have high calcium levels in your blood (hypercalcaemia), or have had kidney stones.
The bottom line
Calcium and vitamin D remain essential. Vitamin K2 (MK-7) has a growing case as their partner, particularly for bone density. But NICE, NOGG and the ROS do not currently recommend it, and larger trials measuring broken bones across wider populations are still needed.
As the evidence grows, prescribing guidance deserves a fresh look. In the meantime, if your GP agrees it is safe for you, vitamin K2 is a low-cost option worth discussing.
Calci-D® and Adcal-D3® are registered trademarks of their respective manufacturers.
References
Diederichsen, A.C.P. et al. (2022) 'Vitamin K2 and D in patients with aortic valve calcification: a randomized double-blinded clinical trial', Circulation, 145(18), pp. 1387–1397. Available at: https://doi.org/10.1161/CIRCULATIONAHA.121.057008
EFSA (2006) Tolerable upper intake levels for vitamins and minerals. Parma: European Food Safety Authority. Available at: https://www.efsa.europa.eu/sites/default/files/efsa_rep/blobserver_assets/ndatolerableuil.pdf
EFSA (2009) 'Scientific opinion on the substantiation of health claims related to vitamin K and maintenance of bone', EFSA Journal, 7(9), p. 1228. Available at: https://doi.org/10.2903/j.efsa.2009.1228
Gregson, C.L. et al. (2025) 'The 2024 UK clinical guideline for the prevention and treatment of osteoporosis', Archives of Osteoporosis, 20(1), p. 119. Available at: https://doi.org/10.1007/s11657-025-01588-3
Huang, Z.B. et al. (2015) 'Does vitamin K2 play a role in the prevention and treatment of osteoporosis for postmenopausal women: a meta-analysis of randomized controlled trials', Osteoporosis International, 26(3), pp. 1175–1186. Available at: https://link.springer.com/article/10.1007/s00198-014-2989-6
Knapen, M.H.J. et al. (2013) 'Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women', Osteoporosis International, 24(9), pp. 2499–2507. Available at: https://pubmed.ncbi.nlm.nih.gov/23525894/
Knapen, M.H.J. et al. (2015) 'Menaquinone-7 supplementation improves arterial stiffness in healthy postmenopausal women: a double-blind randomised clinical trial', Thrombosis and Haemostasis, 113(5), pp. 1135–1144. Available at: https://pubmed.ncbi.nlm.nih.gov/25694037/
Li, T., Wang, Y. and Tu, W.P. (2023) 'Vitamin K supplementation and vascular calcification: a systematic review and meta-analysis of randomized controlled trials', Frontiers in Nutrition, 10, p. 1115069. Available at: https://doi.org/10.3389/fnut.2023.1115069
NHS (n.d.) Vitamin D. Available at: https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-d/
NHS Highland (2026) Calcium and vitamin D (Formulary: Endocrine). Right Decisions. Available at: https://rightdecisions.scot.nhs.uk/tam-treatments-and-medicines-nhs-highland/formularies/highland-formulary/endocrine-system/drugs-affecting-bone-metabolism/osteoporosis/calcium-and-vitamin-d-formulary/
NICE (2026) Osteoporosis: risk assessment (NICE guideline NG259). Available at: https://www.nice.org.uk/guidance/ng259
NICE (n.d.) Osteoporosis – prevention of fragility fractures. Clinical Knowledge Summary. Available at: https://cks.nice.org.uk/topics/osteoporosis-prevention-of-fragility-fractures/
North East London Pharmacy and Medicines Optimisation Team (2023) Calcium and vitamin D (colecalciferol) preparations for adults at risk of osteoporosis. NHS North East London. Available at: https://primarycare.northeastlondon.icb.nhs.uk/wp-content/uploads/2024/01/Calcium-and-vitamin-D-colecalciferol-preparations-for-adults-at-risk-of-osteoporosis-guidance-NEL_12.2023.pdf
Rønn, S.H. et al. (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), pp. 541–549. Available at: https://doi.org/10.1530/EJE-16-0498
Royal Osteoporosis Society (2021) Further food facts and bones. Available at: https://strwebprdmedia.blob.core.windows.net/media/v2pdyew4/ros-further-food-facts-and-bones.pdf
Royal Osteoporosis Society (n.d.) Vitamin D for bones. Available at: https://theros.org.uk/information-and-support/bone-health/vitamin-d-for-bones/
Wasilewski, G.B., Vervloet, M.G. and Schurgers, L.J. (2019) 'The bone–vasculature axis: calcium supplementation and the role of vitamin K', Frontiers in Cardiovascular Medicine, 6, p. 6. Available at: https://doi.org/10.3389/fcvm.2019.00006
Xie, C. et al. (2024) 'Effects of vitamin K supplementation on bone mineral density at different sites and bone metabolism in the middle-aged and elderly population', Bone & Joint Research, 13(12), pp. 750–763. Available at: https://doi.org/10.1302/2046-3758.1312.BJR-2024-0053.R1
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