Vitamin K: The Forgotten Bone Builder

Most people know vitamin K as "the clotting vitamin" — that nutrient doctors mention when you're on blood thinners. And while that role is real and important, it sells vitamin K profoundly short. This fat-soluble vitamin is a master director of calcium in the body, telling it where to go and, just as critically, where not to go. The result: stronger bones, more elastic arteries, healthier metabolism, and for women specifically, meaningful support across the entire arc of reproductive and post-reproductive life.

At Wild Witch Wellness, we believe that understanding why a nutrient matters is just as important as knowing it exists. So let's go deeper.

Vitamin K doesn't just stop bleeding. It is the body's calcium traffic director — building up bones and keeping arteries clear at the same time.

Two forms, two jobs

Vitamin K comes in more than one form — and understanding the difference helps you make better choices at both the table and the supplement shelf.

Plant sources

Vitamin K1 (Phylloquinone)

Found in dark leafy greens, broccoli, Brussels sprouts, and vegetable oils. The dominant form in diet — making up 75–90% of most people's vitamin K intake. Primarily directs blood clotting in the liver. It's relatively well absorbed but sensitive to light; store greens in a cool, dark spot.

Animal & fermented sources

Vitamin K2 (Menaquinone)

Found in aged cheeses, egg yolks, butter, natto, and some meats. Comes in several subtypes (MK-4 through MK-13) — MK-7 is the longest-acting and best-studied for supplementation. K2 is the form that works in bones, arteries, and soft tissues. Most people are low in it.

Why K2 gets the spotlight

You can eat plenty of K1-rich greens and still be functionally low in K2 — the form that does the most for your bones and heart. K1 and K2 are absorbed and used differently; K1 goes mostly to the liver for clotting, while K2 travels to peripheral tissues like bones and blood vessels. Food sources of K2 are limited in Western diets, which is why many practitioners consider supplementation worth discussing — especially for women at higher risk of bone loss or cardiovascular issues.

What Vitamin K does for your body

Vitamin K's defining role is activating a family of proteins called Gla proteins — at least 17 of them in the human body. These proteins can only do their jobs once vitamin K activates them, which is why adequate levels matter far beyond blood clotting alone:

🩸Blood Clotting

Vitamin K activates four of the thirteen proteins needed for blood coagulation. Without it, even small wounds can bleed excessively. This is also why people on blood-thinning medications like warfarin are told to keep vitamin K intake consistent — the drug works by blocking vitamin K's clotting activity.

🦴Bone Building & Preservation

Vitamin K activates osteocalcin, a protein made by bone-building cells that binds calcium and locks it into bone tissue. Without enough K2 to activate it, osteocalcin sits in the bloodstream inactive — and calcium doesn't make it into bones efficiently, no matter how much you take.

🫀Arterial health & anti-calcification

Vitamin K2 activates Matrix Gla Protein (MGP), the body's most potent inhibitor of soft-tissue calcification. MGP prevents calcium from depositing in artery walls — a process that stiffens vessels and dramatically raises cardiovascular risk. Higher K2 intake is consistently associated with greater arterial elasticity and lower coronary heart disease risk.

🍬Blood sugar & insulin sensitivity

Emerging research shows vitamin K2 activates osteocalcin as a hormone that stimulates insulin secretion and enhances insulin sensitivity in peripheral tissues. This makes vitamin K relevant not just for bone and heart health, but for metabolic balance — particularly for women with PCOS or insulin resistance

🧠Neurological function

Vitamin K activates Gas6, a protein involved in neuron survival and the maintenance of the myelin sheath that protects nerve fibers. It also supports the synthesis of sphingolipids — key fats in brain tissue. Vitamin K is concentrated in the brain, and research is beginning to examine its role in cognitive aging and neurological health.

Where to find it in food

K1 is abundant in dark leafy greens — eat them regularly with a fat (olive oil, avocado, nuts) to maximize absorption, since K is fat-soluble. K2 is the harder one to source from a Western diet, and where fermented and traditional foods shine.

Food	Serving	Amount	% Daily Value	Source
Natto (fermented soy beans)	3 oz	850 mcg	708	K2 as MK-7
Collards, frozen, boiled	1/2 cup	530 mcg	442	K1
Spinach, raw	1 cup	145 mcg	121	K1
Kale, raw	1 cup	113 mcg	94	K1
Broccoli, boiled	1/2 cup	110 mcg	92	K1
Edamame from frozen	1/2 cup	21 mcg	18	K1
Pumpkin, canned	1/2 cup	20 mcg	17	K1
Chicken, breast, rotisserie	3 oz	13 mcg	11	K2 as MK4
Cheddar Cheese	1.5 oz	4 mcg	3	K2 as MK4

Source: https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/

---

How much do you actually need?

Unlike most vitamins, vitamin K doesn't have a formal Recommended Dietary Allowance (RDA) — there isn't enough data to set one. Instead, the National Academy of Medicine uses an Adequate Intake (AI) level, based on observed intakes in healthy populations.

These are for total vitamin K (K1 + K2 combined):

Adult women (19+) - 90 mcg/day (AI)

Adult men (19+) - 1120 mcg/day (AI)

Pregnant & Breastfeeding Women - 90 mcg/day

Signs you might be running low

Vitamin K deficiency is rare in healthy adults — but suboptimal K2 status is common in Western populations that eat few fermented foods. Subclinical deficiency may not show up as obvious symptoms but can quietly undermine bone and cardiovascular health over time. Watch for:

• Easy bruising

• Heavy periods

• Bone density loss

• Arterial stiffness

• Calcium supplementing without K2

  • If you take calcium or vitamin D supplements without K2, it's worth reassessing — K2 is needed to direct that calcium where it belongs.

⚠️ If you take blood thinners

Vitamin K directly counteracts the action of warfarin (Coumadin) and similar anticoagulant medications. If you take a blood thinner, the key is consistency — not avoiding vitamin K entirely, but keeping your intake stable from day to day so your medication can be dosed appropriately. Sudden large changes in vitamin K intake (like starting a daily green juice) can affect how the medication works. Always discuss any dietary changes or supplement plans with your prescribing provider

---

Vitamin K & the female body

*Not so fun, fun fact: Women were largely excluded from medical research until the late 20th century, with most studies conducted on men. In 1993, the NIH Revitalization Act of 1993 officially required women to be included in federally funded clinical research. Therefore, on this page, we will ALWAYS talk about women's bodies.

Most existing research on vitamin K and women has focused on bone health in postmenopausal women — a critical area, but only part of the picture. Newer research is uncovering significant roles in PCOS, cardiovascular health, pregnancy, and hormonal metabolism. The field is growing, and the evidence is promising.

Cycle Support

Vitamin K plays a direct role in regulating menstrual blood flow through its clotting activity. Women who experience heavy periods (menorrhagia) may have dysregulated clotting, and some research suggests vitamin K status is relevant here. Additionally, vitamin K's role in reducing inflammation may help ease menstrual cramping and discomfort.

PCOS & Insulin Sensitivity

A randomized controlled trial found that K2 (as MK-7) supplementation at 180 mcg/day for 8 weeks significantly improved insulin sensitivity in women with PCOS — a condition defined in part by insulin resistance and hormonal dysregulation. This makes vitamin K2 a compelling, underutilized tool in an integrative approach to PCOS management.

Pregnancy & Newborn Health

Vitamin K is essential for preventing hemorrhagic disease in newborns — which is why all babies receive a vitamin K injection at birth. During pregnancy, vitamin K supports maternal bone health and healthy blood clotting. K1 crosses the placenta only in small amounts, making colostrum and early breast milk important early sources for the newborn. The recommended intake stays the same during pregnancy (90 mcg/day), but food sources are especially important.

Perimenopause

The years around menopause bring accelerating bone loss as estrogen declines — estrogen normally suppresses bone breakdown, and without it, bones can lose density quickly. Vitamin K2 directly counteracts this: it activates osteocalcin to bind calcium into bone matrix and suppresses osteoclast (bone-breakdown) activity. Observational studies consistently show lower bone loss rates in postmenopausal women with higher K1 intake, and RCTs show K2 (MK-4) improves bone mineral density over 3 years.

Post-Menopause & Heart Health

Women's cardiovascular risk rises significantly after menopause, and arterial calcification is a major contributor. Vitamin K2 — through its activation of Matrix Gla Protein — actively inhibits calcium deposits in artery walls. A large cohort study found higher K2 intake, but not K1, was associated with meaningfully reduced coronary heart disease risk. A 3-year RCT in postmenopausal women also showed K2 (MK-7) supplementation improved arterial elasticity.

---

🌿 The Wild Witch approach

• Eat dark leafy greens daily — kale, spinach, collards, and chard are among the richest K1 sources. Always pair them with a fat (olive oil, avocado, nuts) to maximize absorption.

• Include fermented foods regularly for K2, like fermented soy products, if they work for your body.

• If you supplement with vitamin D3, consider pairing it with K2 (MK-7, 100–200 mcg). They work together — D3 increases calcium absorption, K2 makes sure that calcium goes to bones and not arteries.

• If you eat meat and dairy, prioritize grass-fed sources — animals that graze on green plants have meaningfully higher K2 in their fat and organs.

• If you're perimenopausal or postmenopausal, or if you have PCOS or insulin resistance, a conversation with your practitioner about K2 specifically is worth having — the evidence is growing and the applications are practical.

As always, the most powerful thing you can do is pay attention to your own body. These are patterns and guidelines — not prescriptions. If you suspect you're running low or want to understand your levels more precisely, a simple blood panel and a conversation with an integrative health practitioner can tell you a great deal.