Vitamin K: Blood Clotting and Bone Health

Vitamin K is an essential fat-soluble vitamin best known for its role in blood clotting—the "K" comes from "Koagulation," the German word for coagulation. However, research over the past two decades has revealed equally important roles in bone health and cardiovascular protection, making vitamin K increasingly recognized as vital for healthy aging.

What makes vitamin K particularly interesting is that it exists in two main forms with distinctly different functions and sources: K1 (phylloquinone) from plants and K2 (menaquinone) from fermented foods and animal products. Understanding these differences is key to optimizing your vitamin K status.

                The Calcium Paradox: Vitamin K2 helps solve the "calcium paradox"—why some populations with high calcium intake still have high rates of osteoporosis and arterial calcification. K2 activates proteins that direct calcium into bones (where it's needed) and keep it out of arteries (where it's harmful). Without adequate K2, calcium may end up in the wrong places.
            

120 mcg

AI for Men (K1)

90 mcg

AI for Women (K1)

No RDA

K2 (Emerging Research)

80%

Suboptimal K2 Status

Forms of Vitamin K

Vitamin K1 (Phylloquinone)

Found in green leafy vegetables, K1 is the primary dietary form in Western diets. It's primarily used by the liver for producing blood clotting factors. Most people consuming vegetables regularly get adequate K1.

Vitamin K2 (Menaquinones)

A family of compounds with varying chain lengths (MK-4 through MK-13). The most studied forms are:

MK-4: Found in animal products; short half-life in the body; used by tissues beyond the liver
MK-7: Found in natto (fermented soybeans); long half-life; accumulates to higher levels; particularly effective for bone and cardiovascular health

Blood Clotting

Vitamin K's original discovered function—and still essential today:

Clotting factor activation: Required for factors II, VII, IX, and X to function
Prevents excessive bleeding: Without vitamin K, minor cuts could become life-threatening
Protein C and S: Also activates these anticoagulant proteins, providing balance

Warfarin Interaction: Blood thinners like warfarin work by blocking vitamin K recycling. If you take warfarin, maintain consistent vitamin K intake (don't suddenly increase or decrease) rather than avoiding it entirely. Talk to your doctor before supplementing with vitamin K.

Bone Health

Vitamin K (especially K2) is increasingly recognized as essential for bone health:

Osteocalcin activation: K2 "carboxylates" osteocalcin, enabling it to bind calcium into bone matrix
Bone mineralization: Directs calcium into bones where it strengthens structure
Fracture prevention: Studies show K2 supplementation reduces fracture risk
Osteoporosis treatment: Used therapeutically in Japan for osteoporosis

                The Japan Example: Japan has long used vitamin K2 (specifically MK-4 at 45mg daily) as an approved treatment for osteoporosis. Studies show it can reduce vertebral fractures by up to 80% in postmenopausal women. While Western guidelines haven't caught up, the evidence for K2's bone benefits is substantial.
            

Cardiovascular Protection

Perhaps the most exciting area of vitamin K research involves cardiovascular health:

Matrix Gla-protein (MGP) activation: K2 activates MGP, a potent inhibitor of arterial calcification
Arterial flexibility: May help maintain elastic arteries by preventing calcium deposits
Heart disease risk: Higher K2 intake associated with reduced cardiovascular mortality
Arterial calcification reversal: Some evidence suggests K2 may help reverse existing calcification

Rotterdam Study: This landmark study followed over 4,800 people for 10+ years and found that those in the highest third of vitamin K2 intake had 52% lower risk of severe arterial calcification and 57% lower risk of dying from heart disease. Vitamin K1 showed no such association—the benefit was specific to K2.

Best Food Sources

Vitamin K1 Sources

Kale

817 mcg per cup cooked. Exceptionally rich—provides nearly 700% of daily K1 needs.

Spinach

888 mcg per cup cooked. Another powerhouse green.

Broccoli

220 mcg per cup cooked. Good source with other nutrients.

Brussels Sprouts

219 mcg per cup cooked. Excellent K1 with fiber.

Vitamin K2 Sources

Natto

1,000+ mcg MK-7 per 100g. By far the richest source—Japanese fermented soybeans.

Hard Cheeses

75-100 mcg per 100g. Gouda and Brie are particularly good sources.

Egg Yolks

15-30 mcg per yolk. Pasture-raised eggs contain more K2.

Chicken Liver

13 mcg MK-4 per 100g. Animal source of K2.

K2 and the D3-K2 Synergy

Vitamins D3 and K2 work together in calcium metabolism and are often recommended as a combination:

D3 increases calcium absorption: More calcium enters the bloodstream
K2 directs that calcium: Ensures calcium goes to bones, not arteries
Complementary benefits: Both support bone density through different mechanisms
Safety consideration: Some experts recommend K2 whenever supplementing with D3

                Recommended Pairing: When taking vitamin D3 supplements, consider adding vitamin K2 (100-200 mcg MK-7 or equivalent) to optimize calcium utilization. This is especially important with higher D3 doses (above 2,000 IU) or if you have cardiovascular concerns.
            

Vitamin K and Longevity

Optimal vitamin K status supports healthy aging through:

Bone preservation: Maintains bone density and reduces fracture risk with age
Arterial health: Protects against arterial calcification and stiffening
Cardiovascular protection: Lower risk of heart disease mortality
Brain health: Emerging research suggests K2 may support cognitive function
Metabolic health: Some evidence for improved insulin sensitivity