Overview and Importance
Vitamin K2, also called menaquinone, is a special form of vitamin K that helps direct calcium to the right places in your body—to your bones and teeth instead of your arteries and soft tissues. While vitamin K1 is mainly for blood clotting, K2 focuses on bone health and may protect your heart by preventing calcium buildup in arteries. K2 comes in different forms, with MK-4 and MK-7 being the most important. Your gut bacteria can make some K2, but you need to get most of it from food. Fun fact: K2 was only discovered as distinct from K1 in the 1970s, making it a relatively new vitamin in scientific terms!
Natural Sources vs. Supplements
K2 is found in fermented foods and animal products:
Top K2 Sources: Natto (Japanese fermented soybeans) has the highest amounts—about 1000 mcg per 100g. It's by far the richest food source.
Dairy and Eggs: Hard cheeses (50-100 mcg per 100g), soft cheeses (lower amounts), and egg yolks from pasture-raised chickens (10-30 mcg per yolk).
Meat Sources: Liver and other organ meats contain modest amounts of K2. Chicken and beef have smaller amounts.
Fermented Foods: Sauerkraut, kimchi, and other fermented vegetables contain small amounts of K2.
Supplements: Available as MK-4 or MK-7 forms. MK-7 stays in the blood longer and may be more effective. Most supplements provide 45-180 mcg per dose.
Since K2 foods are not common in typical Western diets, many people consider supplements to get adequate amounts.
Recommended Daily Intake and Dosage
There's no official requirement for K2 specifically, but research suggests helpful amounts:
- General Health: 45-180 mcg daily appears beneficial in studies
- Bone Health: Studies often use 180 mcg of MK-7 daily
- Heart Health: Research suggests 90-360 mcg daily may help prevent artery calcification
- Children: No specific recommendations, but smaller amounts would be appropriate
Most people get very little K2 from their regular diet, so even small amounts from supplements or K2-rich foods can be helpful.
K2 vs K1: Different Jobs
K1 and K2 have different roles in your body:
Vitamin K1: Mainly handles blood clotting. Found in leafy green vegetables. Your body uses it quickly and doesn't store much.
Vitamin K2: Manages calcium placement—helps calcium go to bones and stay out of arteries. Found in fermented foods and animal products. Stays in your body longer than K1.
Different Forms: K2 comes as MK-4 (shorter-acting) and MK-7 (longer-acting). MK-7 may be more effective because it lasts longer in your blood.
You need both K1 and K2, but they do different jobs. K1 is easier to get from food (leafy greens), while K2 requires more specific food choices.
Shortage Risks and Symptoms
K2 shortage is hard to detect but may cause long-term problems:
Bone Effects: May contribute to weak bones and increased fracture risk over time. K2 helps activate proteins that build strong bones.
Heart Effects: May allow calcium to build up in arteries instead of going to bones, potentially increasing heart disease risk.
No Obvious Symptoms: Unlike K1 shortage (which causes bleeding), K2 shortage doesn't cause immediate symptoms. Problems develop slowly over years.
High-Risk Groups: People eating few fermented foods, those with gut bacteria problems (from antibiotics), older adults, and people with heart disease risk factors.
Since most people eat very little K2, mild shortage may be common, but we're still learning about the long-term effects.
Possible Side Effects and Harm
K2 is very safe with no known serious side effects:
Food Safety: K2 from foods like natto and cheese is extremely safe. No toxic effects have been reported from food sources.
Supplement Safety: K2 supplements appear very safe even at high doses. Studies using up to 360 mcg daily show no side effects.
Blood Thinner Interactions: K2 may interact with warfarin and similar blood thinners, but this interaction is much weaker than with K1.
K2 is considered one of the safest vitamins, with no upper limit set due to lack of toxicity concerns.
Interactions and Absorption
K2 works with other nutrients and has some interactions:
Works With: K2 works best with vitamin D and calcium. Vitamin D helps your body make the proteins that K2 activates for bone health.
Take With Fat: Like other fat-soluble vitamins, K2 is better absorbed when taken with fat-containing foods.
Blood Thinners: K2 may slightly affect blood-thinning medications, but much less than K1. Still, people on warfarin should discuss K2 with their doctor.
Gut Health: Healthy gut bacteria can make some K2, so antibiotics or gut problems may reduce natural K2 production.
K2 generally has fewer interactions than K1 and is considered safer for people on blood thinners.
Who Benefits Most from K2
K2 supplements may be especially helpful for:
- Older Adults: Risk for both bone loss and heart disease increases with age, and K2 may help with both.
- People with Heart Disease Risk: Those with high calcium scores in arteries or family history of heart disease.
- Postmenopausal Women: At higher risk for bone loss and may benefit from K2 for bone health.
- People Taking Vitamin D and Calcium: K2 helps direct the calcium to bones instead of soft tissues.
- Those Eating Few Fermented Foods: Most Western diets are very low in K2.
Since K2 foods are uncommon in typical diets, many health-conscious people consider K2 supplements.
How to Choose a Quality K2 Supplement
When selecting a K2 supplement:
- Look for Testing: Choose products with USP, NSF, or ConsumerLab testing for quality assurance.
- Choose MK-7 over MK-4: MK-7 stays in your blood longer and may be more effective. Most studies use MK-7.
- Appropriate Dosing: Look for 45-180 mcg of MK-7. Higher doses aren't necessarily better.
- With Other Nutrients: K2 works well with vitamin D3 and magnesium. Some supplements combine these.
- Form Options: Capsules, softgels, or liquid drops all work. Take with fat for better absorption.
Many bone health supplements now include K2 along with vitamin D and calcium.
Practical Tips for Getting More K2
Boost K2 intake through food and supplements:
Food Sources: Try natto if you can handle the strong taste and texture—it's by far the best source. Include hard cheeses and pasture-raised eggs in your diet.
Fermented Foods: Add sauerkraut, kimchi, or other fermented vegetables to meals for modest amounts of K2.
Supplements: Take K2 supplements with meals containing fat for better absorption. Morning or evening both work fine.
Gut Health: Support healthy gut bacteria with probiotic foods, as they can make some K2.
Since K2 foods are limited, a combination of occasional K2-rich foods plus supplements works well for most people.
Myths and Wrong Ideas
Let's clear up K2 confusion:
Myth: K2 is just a marketing gimmick—K1 is enough. Truth: K2 has different functions than K1, particularly for bone and heart health.
Myth: You can convert K1 to K2 in your body. Truth: Humans can convert very small amounts, but not enough to meet K2 needs.
Myth: All K2 supplements are the same. Truth: MK-7 and MK-4 have different properties, with MK-7 generally being more effective.
Myth: K2 alone will fix bone problems. Truth: K2 works best as part of a complete approach including vitamin D, calcium, and exercise.
K2 is a legitimate nutrient with specific benefits, but it's not a magic bullet—it works best with other bone and heart-healthy practices.
Latest K2 Research
Recent studies on K2 focus on:
Heart Health: Research suggests K2 may help prevent calcium buildup in arteries, but more long-term studies are needed.
Bone Health: Studies show K2 may help maintain bone density, especially when combined with vitamin D and calcium.
Optimal Dosing: Researchers are still determining the best doses of K2 for different health goals.
MK-7 vs MK-4: Studies increasingly focus on MK-7 due to its longer action in the body.
K2 research is growing rapidly, with most evidence supporting its role in bone and heart health.
Call to Action and Next Steps
Ready to explore K2 for bone and heart health? Consider trying natto if you're adventurous, or add more fermented foods and hard cheeses to your diet. If you're taking vitamin D and calcium supplements, talk to your doctor about adding K2 to help direct calcium to your bones. Choose MK-7 supplements if you decide to supplement, and take them with fat-containing meals. Pay attention to your overall bone health approach—K2 works best with vitamin D, calcium, and weight-bearing exercise. Share your experiences with K2 foods or supplements in the comments! For more on bone health, check out our posts on vitamin D, calcium, and magnesium.