Vitamin K2 After 40
After the age of 40, bone density gradually declines and arterial stiffness tends to increase. Vitamin K2 is often promoted as a nutrient that helps direct calcium into bones rather than arteries. Our editorial team looks at what is established, what remains uncertain and how to approach K2 sensibly in midlife.
What vitamin K2 is
Vitamin K is a family of fat-soluble compounds. Vitamin K1 (phylloquinone) comes mainly from green leafy vegetables and is primarily used by the liver to make blood-clotting factors. Vitamin K2 refers to the menaquinones, labelled MK-4 to MK-13 according to the length of their side chain.
MK-4 is found in small amounts in animal foods and is also made in the body from K1. MK-7 and longer menaquinones are produced by bacteria and are found in fermented foods, most famously natto, a Japanese fermented soybean dish, and in some cheeses.
The key function of vitamin K is activating proteins through a process called carboxylation. Besides clotting factors, these include osteocalcin in bone and matrix Gla protein (MGP) in blood vessel walls, which helps inhibit calcification.
The UK does not set a separate recommendation for K2. Government advice suggests about 1 microgram of vitamin K per kilogram of body weight per day for adults, which most people meet through a balanced diet, mostly as K1.
Why it matters more after 40
From midlife, bone loss accelerates, especially in women around and after the menopause, when falling oestrogen speeds up bone turnover. Men also lose bone, more gradually. Osteoporosis affects millions of people in the UK and is a major cause of fractures in later life.
At the same time, arterial calcification and stiffness become more common with age, contributing to cardiovascular risk. Because MGP depends on vitamin K, researchers have asked whether a better vitamin K status might slow vascular calcification.
Studies measuring inactive (uncarboxylated) forms of osteocalcin and MGP suggest that many adults have suboptimal vitamin K status for these extra-hepatic proteins, even when clotting is normal. Whether correcting this improves clinical outcomes is the critical question.
Lifestyle remains the foundation. Weight-bearing and resistance exercise, adequate calcium and protein, sufficient vitamin D, not smoking and moderate alcohol intake all have stronger evidence for protecting bones than any single supplement.
What studies show for bones and arteries
In Japan, MK-4 at a high pharmacological dose of 45 mg per day is approved for osteoporosis. A Cochrane-style meta-analysis by Cockayne and colleagues suggested reduced fracture risk, but many of the included trials were small and from a single country, and some later studies did not confirm the benefits.
A three-year trial by Knapen and colleagues in postmenopausal women found that 180 micrograms per day of MK-7 slowed the decline in bone mineral density and bone strength at certain sites. Results are encouraging, though fracture outcomes were not assessed.
For blood vessels, the observational Rotterdam Study linked higher dietary menaquinone intake with lower coronary calcification and heart disease mortality. Randomised trials testing K2 on vascular calcification have so far shown mixed and mostly modest effects.
| Form | Main sources | Half-life | Research doses |
|---|---|---|---|
| K1 (phylloquinone) | Kale, spinach, broccoli | Hours | Dietary amounts |
| MK-4 | Meat, eggs, butter; supplements | Hours | 45 mg/day (Japan, medical use) |
| MK-7 | Natto, some cheeses; supplements | About 3 days | Typically 90–360 µg/day |
Food, supplements and the vitamin D connection
Western diets contain relatively little MK-7 unless people eat natto or large amounts of hard and soft cheeses such as Gouda, Edam or Brie. Egg yolks, chicken and liver provide some MK-4. Fermented foods such as sauerkraut contain variable amounts.
Supplements usually provide MK-7 at 45–200 micrograms, often combined with vitamin D3. The rationale is that vitamin D increases production of vitamin K-dependent proteins, while K2 activates them, but clinical evidence that the combination is superior is still limited.
In the UK, everyone is advised to consider 10 micrograms (400 IU) of vitamin D daily during autumn and winter, and some groups all year round. This advice applies regardless of whether someone takes K2.
- Include green vegetables daily for K1.
- Consider fermented foods and cheeses as natural K2 sources.
- Take fat-soluble vitamins with a meal containing some fat.
- Do not exceed labelled doses of combined D3 + K2 products.
Safety and the warfarin warning
Vitamin K2 has a good safety record, and no tolerable upper intake level has been set by EFSA due to a lack of reported toxicity. Side effects at usual supplement doses are uncommon.
The critical exception concerns vitamin K antagonists, mainly warfarin in the UK. These anticoagulants work by blocking vitamin K recycling, and even small doses of MK-7 can affect the INR. People on warfarin must not start K2 supplements without consulting their anticoagulation clinic.
Direct oral anticoagulants such as apixaban and rivaroxaban do not act via vitamin K, so K2 is not expected to interfere with them, but it is still wise to tell your doctor about any supplement.
People with liver disease, those with malabsorption conditions or those taking long-term antibiotics or certain cholesterol medicines may have altered vitamin K status and should seek advice rather than self-supplementing.
Editorial conclusions
Vitamin K2 activates proteins involved in bone mineralisation and inhibiting arterial calcification, which makes it relevant to health after 40.
Evidence for bone density is moderately encouraging, while cardiovascular benefits remain uncertain and largely observational.
K2 complements but does not replace exercise, calcium, vitamin D and protein, and anyone on warfarin must seek medical advice first.
Our editorial team suggests reading next about vitamin D in the UK winter, strength training after 40 and calcium intake from food versus supplements.
References
- Knapen MH, Drummen NE, Smit E, et al. Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. Osteoporos Int. 2013;24(9):2499–2507.
- Cockayne S, Adamson J, Lanham-New S, et al. Vitamin K and the prevention of fractures: systematic review and meta-analysis of randomized controlled trials. Arch Intern Med. 2006;166(12):1256–1261.
- Geleijnse JM, Vermeer C, Grobbee DE, et al. Dietary intake of menaquinone is associated with a reduced risk of coronary heart disease: the Rotterdam Study. J Nutr. 2004;134(11):3100–3105.
- Schurgers LJ, Teunissen KJ, Hamulyák K, et al. Vitamin K-containing dietary supplements: comparison of synthetic vitamin K1 and natto-derived menaquinone-7. Blood. 2007;109(8):3279–3283.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Dietary reference values for vitamin K. EFSA J. 2017;15(5):4780.
- Booth SL. Vitamin K: food composition and dietary intakes. Food Nutr Res. 2012;56:5505.
- https://steroidelegalkaufen.com/produkt/anavaros-10-mg-driada-medical/
