There is no official daily recommendation specifically for vitamin K2 in women. Government guidelines set the adequate intake for all forms of vitamin K combined at 90 mcg per day for women aged 19 and older. That number doesn’t distinguish between K1 (found mainly in leafy greens) and K2 (found in fermented foods, cheese, and egg yolks), because nutrition authorities haven’t collected enough data on K2 alone to issue a separate target. In practice, most women meet the 90 mcg threshold primarily through K1, and the amount of K2 they actually need remains an open question.
What we do have are clinical trials that used specific K2 doses for specific health goals, particularly bone health in postmenopausal women. Those numbers give a practical starting point, even if they haven’t been codified into official guidelines.
What the Official Guidelines Actually Cover
The National Institutes of Health sets an adequate intake (AI) for vitamin K at 90 mcg per day for adult women, including during pregnancy and breastfeeding. For teens aged 14 to 18, the AI drops to 75 mcg. These values are based on the intake levels of healthy populations, not on controlled experiments measuring exactly how much is optimal. There wasn’t enough evidence to establish a more precise requirement, so the AI is essentially a best estimate.
Critically, these numbers were built almost entirely around K1, because food composition data for K2 remains limited. No normal reference ranges for K2 blood levels have been established. So when a supplement label says it provides 100 mcg of K2, there’s no government-set benchmark to measure that against.
Doses Used in Bone Health Research
The most relevant clinical data for women comes from studies on postmenopausal bone loss, where K2 plays a role in activating proteins that help deposit calcium into bones rather than arteries. Two forms of K2 dominate the research: MK-4 and MK-7. They behave quite differently in the body, and the doses used in studies reflect that.
MK-7, the form found in most consumer supplements, has a longer half-life, meaning it stays active in the bloodstream longer and can be taken once daily. The most cited trial for bone health in postmenopausal women used 180 mcg of MK-7 per day and found benefits for bone strength over three years. Other trials have gone higher, using 375 mcg of MK-7 daily alongside calcium and vitamin D. That 100 to 200 mcg range is where most MK-7 supplements land, and it aligns with the doses that have shown measurable effects.
MK-4, the other major form, requires dramatically higher doses because the body clears it much faster. Clinical trials typically use 45 mg per day (that’s milligrams, not micrograms, roughly 500 times the dose of a typical MK-7 supplement), often split into three 15 mg doses. This high-dose MK-4 protocol is common in Japanese research and clinical practice for osteoporosis, but it’s far outside what most Western supplement products offer.
MK-4 vs. MK-7: Why the Dose Gap Is So Large
The difference comes down to how long each form circulates in your body. MK-7 has a half-life of several days, so it accumulates with daily dosing and remains active at relatively low amounts. MK-4 is cleared within hours, which is why researchers use such large doses, often divided across the day, to maintain meaningful blood levels.
For most women buying a supplement off the shelf, MK-7 is the more practical option. It’s the form used in the majority of widely available products, it requires only one daily dose, and effective amounts (100 to 200 mcg) fit into a single small capsule. If you’re specifically looking at MK-4, be aware that the research-backed dose is 45 mg per day, and lower-dose MK-4 supplements haven’t been well studied for bone outcomes.
During Pregnancy and Breastfeeding
The adequate intake for vitamin K doesn’t change during pregnancy or breastfeeding for adult women. It stays at 90 mcg per day. For pregnant or nursing teens, it’s 75 mcg. Intake at these levels is not associated with increased risk of birth defects, preterm delivery, low birth weight, or developmental effects on the child.
Most prenatal vitamins include some vitamin K, though amounts vary. If you’re considering a standalone K2 supplement during pregnancy, the evidence base for doses above the AI is thin. The high-dose trials (180 mcg and above of MK-7) were conducted in postmenopausal women, not pregnant populations.
Is There an Upper Limit?
No tolerable upper intake level has been set for any form of vitamin K, including K2. This doesn’t mean unlimited amounts are safe. It means the research hasn’t identified a clear toxicity threshold, so authorities chose not to set one rather than guess. Vitamin K in its natural forms (K1 and K2) has not shown toxicity in studies even at high doses, which is part of why no ceiling exists.
The major exception involves blood-thinning medications. Vitamin K directly opposes the mechanism of warfarin and similar drugs. Even modest, consistent K2 intake can shift how well these medications work. If you take a blood thinner, your vitamin K intake (from food and supplements combined) needs to stay stable day to day, and any changes should be coordinated with whoever manages your dosing.
Food Sources of K2
K2 is harder to get from food than K1, which is abundant in spinach, kale, and broccoli. The richest dietary source of K2 by a wide margin is natto, a Japanese fermented soybean dish that delivers roughly 1,000 mcg per serving. Few Western diets include natto regularly.
More familiar sources include hard and aged cheeses (like Gouda and Edam), egg yolks, butter from grass-fed cows, and dark meat chicken. These provide meaningful but smaller amounts. A serving of Gouda contains roughly 20 to 75 mcg of K2 depending on the aging process. Egg yolks provide smaller amounts per egg. Your gut bacteria also produce some K2 in the large intestine, though exactly how much of that your body absorbs and uses remains unclear.
Because K2 is fat-soluble, it absorbs best when eaten with a meal containing some fat. The same applies to supplements. Taking a K2 capsule with breakfast or dinner improves absorption compared to taking it on an empty stomach.
Practical Takeaway for Daily Dosing
For general health, 90 mcg of total vitamin K per day is the baseline for adult women, and most of that can come from K1-rich vegetables. If you’re supplementing K2 specifically, the most common and well-studied dose for MK-7 is 100 to 200 mcg per day. Postmenopausal women focused on bone health may see benefits at the higher end of that range or slightly above (up to 375 mcg was used in trials with calcium and vitamin D). For MK-4, the research-supported dose is 45 mg per day split into three doses, a protocol that requires dedicated high-dose supplements rather than typical multivitamins.
K2 supplements are often paired with vitamin D, since the two work together in calcium metabolism. Many combination products reflect this, bundling 100 to 200 mcg of MK-7 with a standard vitamin D3 dose. Taking K2 alongside vitamin D and adequate calcium is the pattern most closely studied for bone outcomes in women.