Should I take vitamin K2 with vitamin D?

Many experts recommend pairing D3 with K2 (MK-7). Both affect calcium metabolism and their effects may be synergistic — D3 increases calcium absorption while K2 directs it to bones.

Does vitamin K interact with warfarin?

Significantly. Vitamin K and warfarin directly antagonize each other. Patients on warfarin must keep vitamin K intake consistent — not eliminate it, but not dramatically increase it. Discuss with your doctor.

What dose of K2 MK-7 is recommended?

Typically 100–200 mcg/day MK-7 for bone and arterial health. This is above what most diets provide (unless you eat natto regularly).

Is natto the only good K2 source?

It’s by far the richest. Aged cheeses and egg yolks provide modest K2. For vegans not eating natto, a MK-7 supplement (from natto-derived menaquinone) is the practical option.

Can vitamin K reduce bone fracture risk?

A Japanese meta-analysis showed K2 supplementation reduced vertebral fractures by 60% and hip fractures by 77% in postmenopausal women. Western evidence is less consistent — partly because Western diets already have more K than many East Asian diets studied.

Vitamin K: K1 vs K2, Blood Clotting, and Bone Health

K1 vs K2: Two Very Different Vitamins

Vitamin K1 (phylloquinone): found in green vegetables. Primarily used by the liver for clotting factor synthesis. Short half-life — used rapidly. Vitamin K2 (menaquinones, especially MK-4 and MK-7): found in fermented foods and some animal products. Longer half-life (MK-7 lasts 3 days vs hours for K1). Activates proteins that direct calcium to bones and away from arteries.

Blood Clotting

Vitamin K activates clotting factors II, VII, IX, X and anticoagulant proteins C and S. Without vitamin K, blood cannot clot — small cuts bleed profusely. Warfarin (coumadin) works by blocking vitamin K recycling. People on warfarin must maintain consistent vitamin K intake (not eliminate it).

Bone Health: The Underappreciated Role

Osteocalcin is a bone matrix protein that requires vitamin K2 (specifically MK-7) for carboxylation — the process that allows osteocalcin to bind calcium to bone. Uncarboxylated osteocalcin cannot do this job. Low vitamin K2 → calcium floats free → deposits in arteries (calcification) rather than bones. The K2-D3 combination is increasingly recognized as important for bone and cardiovascular health.

Best Food Sources of K1

Kale (100g raw): 704 mcg. Spinach (100g raw): 483 mcg. Collard greens (100g cooked): 623 mcg. Swiss chard (100g cooked): 572 mcg. Brussels sprouts (100g cooked): 140 mcg. Broccoli (100g raw): 102 mcg.

Best Food Sources of K2

Natto (100g fermented soybeans): 1103 mcg MK-7 — extraordinary source. Hard cheeses (Gouda, aged): 49–75 mcg MK-4 per 100g. Egg yolks: 15–25 mcg MK-4. Chicken liver: 13 mcg. Dark chicken meat: 10 mcg. Fermented dairy (kefir): small amounts.

K2 and Arterial Health

Matrix Gla Protein (MGP) is produced by arterial wall cells and requires vitamin K2 to be activated. Activated MGP prevents calcium from depositing in arterial walls. Low K2 → unactivated MGP → arterial calcification → increased cardiovascular risk. Countries with highest natto consumption (Japan) have lowest rates of cardiovascular disease — though confounders exist.