Every tissue in your body needs essential nutrients like amino acids, fatty acids, minerals, and vitamins to function properly—and your bones are no exception. For strong, healthy bones, key nutrients like Vitamin K2 are vital.
Recent research has highlighted the importance of Vitamin K2 for both bone health and preventing calcium build-up in the arteries (vascular calcification). This makes it a key nutrient for anyone focusing on longevity.
Why should you consider supplementing with Vitamin K2 as part of your health journey? Let’s explore in this Avea article.
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What is vitamin K?
Vitamin K, the star of the fat-soluble vitamin K family, is a group of compounds sharing the same chemical structure: 2-methyl-1,4-naphthoquinone.
Naturally present in some foods and available as dietary supplements, vitamin K comes in two primary forms:
- phylloquinone (vitamin K1)
- menaquinones (vitamin K2)
The K family of vitamins is essential for blood clotting, calcium regulation, and antioxidant defence.
Whilst these vitamins share a core chemical structure, they differ in their side chains, which affect how they’re absorbed, transported, and utilised in your body.
Types of vitamin K: K1 vs. K2
Vitamin K1 is mostly found in green leafy vegetables—think kale, spinach, and broccoli. It’s the main form of vitamin K in your diet.
On the other hand, K2 is mainly produced by bacteria and found in small amounts in animal-based and fermented foods. Interestingly, your gut bacteria also produce K2.
Vitamin K2 exists in several forms, but the long-chain Menaquinone-7 (MK-7) has been shown to be more effective in humans than the shorter-chain MK-4.
This is largely due to MK-7’s superior bioavailability and longer half-life. Both MK-4 and MK-7 are well absorbed, with MK-4 reaching peak levels in the blood two hours after intake, and MK-7 peaking at four hours.
MK-4 rapidly disappears from the bloodstream, whilst MK-7 remains active in the body for around 72 hours. For those seeking the maximum benefit from vitamin K2, MK-7 is the optimal choice.
Reap the benefits of K2 and more
- Address common nutrient deficiencies like Magnesium, Omega-3, and Vitamin D.
- Support immune and overall health.
- Enhance your energy and vitality.
The Essentials are packed with vegan, essential micronutrients: Vitamin D3, Vitamin K2, Zinc, Magnesium and Omega-3. Support your immune system, brain and heart health, to build your foundation.
Why is Vitamin K2 so important?
Research suggests that calcification in the arteries can start as early as childhood. This makes early supplementation with vitamin K2 crucial for promoting a healthy cardiovascular system and potentially lowering the risk of poor bone health later in life.
Vitamin K makes four proteins among the 13 that are needed for blood clotting (coagulation).
It is now widely accepted that sufficient intake of vitamin K2 is not only key for maintaining strong bones, but also for reducing the risk of vascular issues.
Yet, most of us may be deficient in this vital nutrient due to modern dietary habits and changes in food production.
Beyond bone and heart health, vitamin K2 offers further potential benefits, including supporting cognitive function, eye health, prostate health, and even the immune system (working as a cofactor alongside vitamin D).
How your body absorbs vitamin K
Just like other fat-soluble vitamins, vitamin K needs a bit of digestive help to be absorbed. Bile and pancreatic enzymes mix vitamin K into micelles in your small intestine.
From there, it travels to your liver before being sent off to various tissues in your body, including the brain, heart, pancreas, and bones.
Despite being essential, only small amounts of vitamin K circulate in the blood at any given time, as it’s metabolised quickly and excreted in urine and faeces.
The role of gut bacteria in vitamin K production
Your gut bacteria also produce vitamin K, particularly long-chain menaquinones (K2).
These forms of vitamin K are found in the large intestine, though how much your body absorbs and uses is still up for debate.
Experts believe these gut-made menaquinones contribute to your overall vitamin K requirements, but the exact amount is uncertain [1].
How much vitamin K do you really need?
These numbers vary by age and gender, so there’s no one-size-fits-all approach.
Unlike some other vitamins, there isn’t enough solid evidence to establish an Estimated Average Requirement (EAR) for vitamin K.
Instead, we use Adequate Intake (AI) levels to guide recommendations.
Adequate Intake (AI) levels for vitamin K
Wondering how much vitamin K you need? Here’s a handy chart to break it down for you, based on age and gender:
| Age | Male | Female | Pregnancy | Lactation |
| Birth to 6 months | 2.0 µg | 2.0 µg | — | — |
| 7–12 months | 2.5 µg | 2.5 µg | — | — |
| 1–3 years | 30 µg | 30 µg | — | — |
| 4–8 years | 55 µg | 55 µg | — | — |
| 9–13 years | 60 µg | 60 µg | — | — |
| 14–18 years | 75 µg | 75 µg | 75 µg | 75 µg |
| 19+ years | 120 µg | 90 µg | 90 µg | 90 µg |
So, for most of us, the daily intake of vitamin K ranges from 75 µg during adolescence to 120 µg for adult males. Women, pregnant, or breastfeeding folks need slightly less—around 90 µg per day.
Food sources of vitamin K
Vitamin K comes from a variety of food sources, primarily split into two forms:
1. Vitamin K1 food sources
Phylloquinone is mainly found in green leafy vegetables, vegetable oils, and certain fruits.
Some of the most common food sources in the diet include spinach, broccoli, iceberg lettuce, and oils like soybean and canola oil.
Although meat, dairy, and eggs contain lower levels of phylloquinone, they do have modest amounts of menaquinones, which we’ll get into later.
2. Vitamin K2 food sources
Menaquinones are a bit more niche, often coming from bacterial sources. A prime example is natto, a traditional Japanese dish made from fermented soybeans, which contains particularly high levels of menaquinone-7 (MK-7).
Other fermented foods, such as cheese, also contain menaquinones, though the specific amounts vary based on the bacterial strains used in the fermentation process.
Interestingly, animals can synthesise MK-4 from a synthetic form of vitamin K (menadione), which is sometimes added to poultry and swine feed. As a result, poultry and pork products can contain MK-4 if their feed includes menadione.
Vitamin K bioavailability
Not all vitamin K is absorbed equally. Whilst vitamin K1 in its free form has an absorption rate of around 80%, when it comes from food sources, its absorption is significantly lower.
This is because phylloquinone in plant foods is bound to chloroplasts, making it less bioavailable than when consumed from oils or supplements.
For example, your body absorbs only 4% to 17% of the phylloquinone from spinach compared to a supplement. Eating vegetables with some fat can improve absorption, but it’s still less efficient than oils.
Research suggests that long-chain menaquinones (K2) might have higher absorption rates than phylloquinone from vegetables.
Vitamin K content in common foods
Here’s a quick look at how much vitamin K you’ll find in various foods. Note that the values are mostly for phylloquinone (K1), unless otherwise stated.
| Food | Micrograms (µg) per serving | Percent DV* |
| Natto, 3 ounces (as MK-7) | 850 µg | 708% |
| Collards, frozen, boiled, ½ cup | 530 µg | 442% |
| Turnip greens, frozen, boiled, ½ cup | 426 µg | 355% |
| Spinach, raw, 1 cup | 145 µg | 121% |
| Kale, raw, 1 cup | 113 µg | 94% |
| Broccoli, chopped, boiled, ½ cup | 110 µg | 92% |
| Soybeans, roasted, ½ cup | 43 µg | 36% |
| Carrot juice, ¾ cup | 28 µg | 23% |
| Soybean oil, 1 tablespoon | 25 µg | 21% |
| Edamame, frozen, prepared, ½ cup | 21 µg | 18% |
| Pumpkin, canned, ½ cup | 20 µg | 17% |
| Pomegranate juice, ¾ cup | 19 µg | 16% |
| Okra, raw, ½ cup | 16 µg | 13% |
| Salad dressing, Caesar, 1 tablespoon | 15 µg | 13% |
| Pine nuts, dried, 1 ounce | 15 µg | 13% |
| Blueberries, raw, ½ cup | 14 µg | 12% |
| Iceberg lettuce, raw, 1 cup | 14 µg | 12% |
| Chicken, breast, rotisserie, 3 ounces (as MK-4) | 13 µg | 11% |
| Grapes, ½ cup | 11 µg | 9% |
| Vegetable juice cocktail, ¾ cup | 10 µg | 8% |
| Canola oil, 1 tablespoon | 10 µg | 8% |
| Cashews, dry roasted, 1 ounce | 10 µg | 8% |
| Carrots, raw, 1 medium | 8 µg | 7% |
| Olive oil, 1 tablespoon | 8 µg | 7% |
| Ground beef, broiled, 3 ounces (as MK-4) | 6 µg | 5% |
| Figs, dried, ¼ cup | 6 µg | 5% |
| Chicken liver, braised, 3 ounces (as MK-4) | 6 µg | 5% |
| Ham, roasted or pan broiled, 3 ounces (as MK-4) | 4 µg | 3% |
| Cheddar cheese, 1½ ounces (as MK-4) | 4 µg | 3% |
| Mixed nuts, dry roasted, 1 ounce | 4 µg | 3% |
| Egg, hard boiled, 1 large (as MK-4) | 4 µg | 3% |
| Mozzarella cheese, 1½ ounces (as MK-4) | 2 µg | 2% |
| Milk, 2%, 1 cup (as MK-4) | 1 µg | 1% |
| Salmon, sockeye, cooked, 3 ounces (as MK-4) | 0.3 µg | 0% |
| Shrimp, cooked, 3 ounces (as MK-4) | 0.3 µg | 0% |
The U.S. Food and Drug Administration (FDA) has set the Daily Value (DV) for vitamin K at 120 µg for adults and children aged 4 years and older. Foods providing 20% or more of the DV are considered high in vitamin K.
Vitamin K in supplements
200 µg of highly bioavailable K2
- Boost Vitamin K2 levels.
- Address common nutrient deficiencies like Magnesium, Omega-3, and Vitamin D.
- Support immune and overall health.
- Enhance your energy and vitality.
What is the best form of vitamin K in supplements?
When it comes to supplementing with vitamin K, the best form for optimal health benefits is Vitamin K2 (as MK-7).
Despite its importance, many of us are deficient in K2 due to modern diets and food processing.
Here’s why MK-7 stands out for different life stages:
- For children:
Vitamin K2 (MK-7) is essential for proper bone development during childhood. Without it, calcium can’t be efficiently utilised, leading to weaker bones. - For active adults:
By our mid-20s, we reach peak bone mass. Maintaining bone health beyond this point requires more than just calcium intake; Vitamin K2 ensures that calcium is effectively incorporated into bones. - For women in menopause:
During menopause, hormonal changes increase the risk of bone loss and cardiovascular issues. Vitamin K2 is crucial for supporting bone density and preventing arterial calcification. - For healthy ageing:
As we age, the risk of bone and heart problems rises. Vitamin K2 helps regulate calcium, preventing it from accumulating in the arteries and contributing to conditions like atherosclerosis.
Vitamin K deficiency
Vitamin K deficiency becomes clinically significant when prothrombin time (how long it takes for blood to clot) increases due to a drop in prothrombin activity.
Severe cases can lead to bleeding and haemorrhage, the hallmark symptoms of vitamin K deficiency.
Because vitamin K is essential for osteocalcin carboxylation in bone, a deficiency may also reduce bone mineralisation and contribute to osteoporosis.
Who is at risk of inadequate vitamin K levels?
- Newborns without vitamin K treatment
Newborns are at higher risk of vitamin K deficiency because vitamin K doesn’t easily cross the placenta. Without treatment, this can cause bleeding in various parts of the body. It’s especially dangerous if it results in sudden intracranial bleeding, which has a high mortality rate.
- People with malabsorption disorders
Those with conditions like cystic fibrosis, celiac disease, ulcerative colitis, and short bowel syndrome often struggle to absorb vitamin K properly. Besides, those who have had bariatric surgery may have low vitamin K levels, though clinical signs aren’t always apparent. These folks may need to monitor their vitamin K levels and, in some cases, take supplements.
Symptoms of vitamin K deficiency
- Feeling sleepy
- Throwing up
- Seizures
- Bruising
- Small red spots (petechiae)
- Nosebleeds
- Yellowing of the skin and eyes (jaundice)
- Pale skin
- Bloody, dark, sticky poop
Health benefits of vitamin K supplements
Vitamin K is a key player in two major health concerns: bone health and heart health. Let’s explore how it may contribute to each.
1. Role of vitamin K in bone health and osteoporosis
Osteoporosis, characterised by weak and brittle bones, is a significant public health issue affecting over 10 million adults in the U.S., with women making up 80% of the cases.
Whilst calcium and vitamin D are often the focus when it comes to bone health, vitamin K has also garnered attention for its potential role in reducing the risk of osteoporosis.
Vitamin K acts as a cofactor for the gamma-carboxylation of several proteins, including osteocalcin, a major protein in bone.
Some studies have linked high levels of undercarboxylated osteocalcin (which indicates insufficient vitamin K activity) with lower bone mineral density.
Whilst some research supports a connection between higher vitamin K intake and better bone mineral density or a lower incidence of hip fractures, the findings are mixed.
Does vitamin K supplementation help with osteoporosis?
Research on vitamin K supplementation’s impact on osteoporosis is inconclusive.
A 2006 meta-analysis reviewed 13 trials and found that vitamin K, particularly MK-4, improved bone mineral density in postmenopausal women and reduced fracture rates. These trials were mostly conducted in Japan, using pharmacological doses of MK-4 (45 mg/day).
Recent studies on MK-7, a more bioavailable form of vitamin K2, have also shown positive results. In one trial, MK-7 supplementation (180 µg/day for 3 years) improved bone strength and reduced vertebral height loss in postmenopausal women.
However, other studies, such as one involving 381 postmenopausal women supplemented with either phylloquinone or MK-4, found no significant effect on bone mineral density despite lowering levels of undercarboxylated osteocalcin.
The inconsistent results across studies may be due to the inclusion of vitamin D and calcium in some trials, making it difficult to isolate the effects of vitamin K on bone health.
In Japan and parts of Asia, MK-4 is used in pharmacological doses (45 mg) to treat osteoporosis.
The European Food Safety Authority has recognised vitamin K’s role in maintaining normal bones, but no such health claim has been approved by the FDA in the U.S.
2. Role of vitamin K in heart health and coronary heart disease
Vascular calcification, a known risk factor for coronary heart disease (CHD), reduces the elasticity of arteries and increases the likelihood of heart problems.
One vitamin K-dependent protein, matrix Gla-protein (MGP), might play a role in preventing vascular calcification.
Animal studies suggest that inadequate vitamin K levels lead to undercarboxylated MGP, which could increase vascular calcification and the risk of coronary heart disease, particularly in those with chronic kidney disease.
Can vitamin K2 supplement help with heart health?
Observational studies have found promising links between menaquinone (vitamin K2) intake and heart health.
In a Dutch study of 564 postmenopausal women, higher vitamin k2 intake (but not vitamin k1) was associated with less coronary calcification.
Another study of over 4,800 men and women found that those with higher vitamin K2, intake had a lower risk of severe aortic calcification and coronary heart disease mortality.
Those in the highest tertile of K2 intake had up to 57% lower risk of CHD mortality compared to those with the lowest intake. However, vitamin K1 intake showed no effect on coronary health.
Despite these observational findings, few clinical trials have tested whether vitamin K supplementation can reduce arterial calcification or coronary heart disease risk.
One notable study involving 388 healthy men and postmenopausal women found that whilst vitamin K1 supplementation didn’t significantly reduce coronary artery calcification overall, participants who adhered to the protocol had less calcification progression compared to the control group. The effect was even more pronounced in participants with pre-existing calcification.
Though the data suggest that K2 may protect against arterial calcification and coronary heart disease, more research is needed. The role of different forms of vitamin K in heart health, particularly in those with chronic kidney disease, remains an active area of investigation.
3. How does vitamin K2 work with D3 and Magnesium?
- Vitamin D3 helps your body absorb calcium from the diet. However, without enough vitamin K2, the calcium absorbed may not be properly directed to the bones and could deposit in arteries or soft tissues, potentially leading to calcification and health problems. Vitamin K2 activates proteins (like osteocalcin and Matrix Gla-protein) that guide calcium to the bones and prevent it from depositing in the arteries, thus working synergistically with D3.
- Magnesium supports the activation of vitamin D3. It is necessary for converting inactive vitamin D into its active form, which the body can then use to regulate calcium absorption. Magnesium also supports healthy bones by helping in calcium metabolism, and it works alongside vitamin K2 and D3 to maintain the balance between calcium being used for bone strength and preventing calcium build-up in soft tissues.
In short, Vitamin K2 ensures that the calcium absorbed through vitamin D3 is deposited in the right places (bones, not arteries), whilst magnesium enhances both vitamin D3 function and overall calcium metabolism. Together, they form a vital combination for bone and heart health.
Safety and side effects of vitamin K supplements
The Food and Nutrition Board has not set an upper limit for vitamin K because of its low toxicity risk.
In fact, it is reported that no adverse effects have been observed from consuming vitamin K in either food or supplements, in humans or animals.
This makes vitamin K one of the safer nutrients to consume, with no established risks from excessive intake.
Vitamin K interactions with medications
Although vitamin K itself poses little toxicity risk, it does interact with several medications.
Besides, some drugs can impact vitamin K levels in the body. If you’re taking any of the medications listed below, it’s important to discuss your vitamin K intake with your healthcare provider to avoid potential complications.
- Warfarin (Coumadin) and similar anticoagulants
One of the most significant interactions is between vitamin K and anticoagulants like warfarin (Coumadin) and its European cousins, phenprocoumon, acenocoumarol, and tioclomarol. These drugs work by antagonising vitamin K, thereby depleting the body of vitamin K-dependent clotting factors.
- Antibiotics
Certain antibiotics can disrupt vitamin K status by destroying the bacteria in the gut that produce it. This risk is higher with antibiotics like cephalosporins (e.g. cefoperazone) that not only kill bacteria but might also inhibit vitamin K activity directly.
- Bile acid sequestrants
Medications such as cholestyramine (Questran) and colestipol (Colestid) are used to lower cholesterol by preventing the reabsorption of bile acids. Unfortunately, this also reduces the absorption of fat-soluble vitamins like vitamin K.
- Orlistat
Orlistat, a popular weight-loss drug available as both Alli (over-the-counter) and Xenical (prescription), works by reducing the absorption of dietary fat. Because vitamin K is a fat-soluble vitamin, orlistat can also reduce its absorption.
FAQs
Why is vitamin K3 (menadione) is no longer used?
Once upon a time, menadione (aka vitamin K3) was a synthetic form of vitamin K. However, lab studies in the ’80s and ’90s showed that it could damage liver cells, so it’s no longer used in supplements or fortified foods.
References
