Most people have heard of vitamin D for bones and omega-3 for the heart, but vitamin K2 rarely gets the same attention, despite playing a surprisingly central role in both. Specifically, the MK-7 form of K2, a long-chain menaquinone found in fermented foods and animal products, has a longer half-life in the body than shorter-chain forms, which means it stays active for longer and reaches more tissues. That biological persistence is a large part of why researchers have focused on it.
The core function of K2 MK-7 is directing calcium traffic. It activates two proteins, osteocalcin and matrix Gla protein (MGP), that respectively pull calcium into bone and prevent it from depositing in blood vessel walls. Without adequate K2, both processes can become inefficient, regardless of how much calcium or vitamin D you consume. That distinction matters particularly as you age, when the risk of both bone thinning and arterial stiffness increases.
K2 tends to be overlooked partly because it is not the form of vitamin K most people encounter. Vitamin K1, found in green leafy vegetables, is well-established as essential for blood clotting and is the form referenced in most general nutrition guidance. K2 comes mostly from fermented and animal foods that are less common in many modern diets, which is one reason dietary intake can fall short without anyone realising it.
What K2 MK-7 Actually Does in the Body
When you eat calcium-rich foods or take a calcium supplement, the mineral needs to go somewhere. Vitamin K2 MK-7 activates osteocalcin, the protein responsible for binding calcium into bone matrix. Without sufficient K2 to carboxylate (activate) this protein, osteocalcin circulates in an undercarboxylated form and becomes far less effective at mineralising bone. A meta-analysis reviewed in NutraIngredients noted that prospective data link poorer osteocalcin carboxylation, a marker of lower vitamin K status in tissues outside the liver, with higher fracture risk.
The cardiovascular side of K2 function works through a different protein. MGP is the most potent known inhibitor of vascular calcification, and it also requires vitamin K2 to become active. This is why the Rotterdam Study, published in 2004 in the Journal of Nutrition, was significant: it was one of the first large prospective studies to show that adequate menaquinone intake was associated with less aortic calcification and lower all-cause mortality. The finding pointed to K2 as something relevant to arterial health, not only bone density.
Beyond bone and cardiovascular research, a peer-reviewed review on the molecular pathways of K2-7 found that MK-7 also upregulates osteoprotegerin, a protein that inhibits bone resorption, and that emerging evidence links it to potential benefits in peripheral neuropathy, diabetes management, and neurodegenerative conditions including Alzheimer's disease. These areas are at earlier stages of research than the bone and cardiovascular evidence, but they indicate that K2's biological reach extends further than its traditional role.
K1 Versus K2: Not the Same Vitamin
The "vitamin K" label groups together compounds with meaningfully different behaviour. Vitamin K occurs in two primary natural forms: phylloquinone (K1), concentrated in green leafy vegetables and algae, and menaquinones (K2), found in fermented and animal foods. K1 is absorbed efficiently from dietary sources and is rapidly used by the liver, primarily for clotting factor production. K2, especially the long-chain MK-7 form, is transported more widely through the bloodstream and reaches bone and vascular tissue in meaningful concentrations.
This difference in distribution explains why eating plenty of spinach and kale does not guarantee adequate K2 status. The two forms are not interchangeable at a tissue level, even though both contribute to overall vitamin K activity in the body. A safety evaluation published in Scientific Reports confirmed that MK-4 and MK-7, the two most studied forms of K2, both support bone and cardiovascular health, but noted that MK-7's superior bioavailability distinguishes it from shorter-chain forms including MK-4.
Food Sources of Vitamin K2
The richest dietary source of MK-7 is natto, a Japanese fermented soybean product, which contains substantially more K2 than any other food. It is an acquired taste that many people outside Japan find strong, but it remains the most concentrated whole-food source available. Beyond natto, K2 is present in fermented cheeses, egg yolks, chicken liver, and certain fermented dairy products. MK-7 is found in foods long consumed by humans, including cabbage and yogurt, though at lower concentrations than natto.
For people living in Hong Kong, natto is available in Japanese supermarkets and some health food stores. Hard and semi-hard aged cheeses, common in European-style dining, also contribute MK-2 in the MK-4 to MK-9 range depending on bacterial strains used in fermentation. Animal liver and egg yolks provide modest amounts. The challenge is that, unlike vitamin K1 from vegetables, K2 is not widely distributed across staple foods, and a diet low in fermented products can easily result in low intake without any obvious sign of deficiency in the short term.
Vitamin K2 Deficiency: Who Is at Greater Risk
Overt vitamin K deficiency, meaning clinically significant bleeding due to impaired clotting, is uncommon in healthy adults. But inadequate K2 status, where extrahepatic tissues including bone and blood vessels have insufficient supply, is a subtler and more common problem. Because the liver preferentially retains K1 for clotting purposes and extrahepatic tissues depend more heavily on circulating K2, someone can have normal clotting function while still having suboptimal bone and vascular K2 activity.
Populations likely to have lower K2 intake include people who eat little or no fermented food, those on long-term antibiotic courses that disrupt gut bacteria (which synthesise small amounts of K2), people with fat malabsorption conditions since K vitamins are fat-soluble, and older adults whose dietary variety may have narrowed. A clinical perspective review identifies osteoporosis, cardiovascular disease, chronic kidney disease, and diabetes among the conditions where vitamin K2 status is thought to be particularly relevant, though this reflects an area of active research rather than established clinical protocol in all settings.
Supplementation: What the Evidence Supports on Dosage
For people who cannot or do not regularly eat K2-rich foods, MK-7 supplements are widely available. The question of dosage has become clearer following a November 2025 analysis by the Council for Responsible Nutrition (CRN), which established for the first time a supplemental Highest Observed Intake (HOI) level of 375 µg per day for adults. This figure is not a recommended dose but a safety ceiling derived from observed intake data, confirming that MK-7 supplements used within this range carry a strong safety record.
Dr Cees Vermeer, Professor at the Cardiovascular Research Institute Maastricht and widely regarded as among the most published researchers on vitamin K2, has noted that MK-7 "has a much higher efficacy than other forms of vitamin K" and that it is the only form of K2 found to be effective for preventing bone loss at doses below 200 micrograms per day. That observation highlights why MK-7 has attracted more clinical research attention than shorter-chain menaquinones: meaningful effects appear at relatively modest doses. The Scientific Reports safety study also confirmed that MK-7 is well tolerated in toxicological evaluation.
One important practical note: vitamin K2 supplements interact with warfarin (and other vitamin K antagonist anticoagulants). If you take a blood-thinning medication of this type, the decision to supplement with any form of vitamin K is one to discuss with the doctor managing your medication, since even modest changes in K intake can affect your INR levels.
Reading the Labels: MK-7 Versus MK-4
Supplements labelled "vitamin K2" may contain MK-4, MK-7, or a blend. The distinction matters. MK-4 has a much shorter half-life, meaning it clears the bloodstream faster and requires higher or more frequent doses to maintain tissue-level activity. MK-7, derived from fermented sources such as natto, remains active for significantly longer, which is why it has become the preferred form in most current K2 research and many commercially available supplements.
When comparing products, look for the specific form listed on the label rather than treating all K2 supplements as equivalent. Dose, form, and whether the supplement is taken with a fat-containing meal (necessary for absorption, since K2 is fat-soluble) all affect how much K2 your body actually absorbs and uses.
What Type of Practitioner to Consult
If your interest in K2 stems from concerns about bone density, a conversation with a doctor who manages osteoporosis or metabolic bone disease, or a registered dietitian who can assess your overall nutrient intake, is a reasonable starting point. Bone density concerns are typically evaluated through DEXA scanning, and K2 status can be assessed indirectly through markers like undercarboxylated osteocalcin, though this test is not part of standard routine blood panels in most Hong Kong clinics.
For cardiovascular concerns related to arterial calcification, a cardiologist or internist is better placed to contextualise K2 within your broader cardiovascular risk profile. K2 is one piece of a larger picture that includes blood pressure, lipid levels, glucose metabolism, and lifestyle factors. No single nutrient addresses that picture alone.
If you want to explore practitioners with relevant specialisations across Hong Kong and the Greater Bay Area, you can find and compare them by specialty on Healwith.
