Vitamin D3 vs K2
Vitamin D3 and Vitamin K2 are two of the most important fat-soluble vitamins for long-term health. While they serve different primary functions, they work synergistically — especially when it comes to calcium metabolism and bone health.
Vitamin D3: The Sunshine Vitamin
D3 is essential for calcium absorption, immune regulation, and mood. Without adequate D3, your body absorbs only 10–15% of dietary calcium. With sufficient D3, absorption jumps to 30–40%. It's also a key player in immune defense and has been linked to lower rates of respiratory infections.
Vitamin K2: The Traffic Director
K2 (specifically the MK-7 form) activates proteins that direct calcium into bones and teeth — and away from arteries and soft tissues. Without K2, the extra calcium absorbed thanks to D3 might end up in the wrong places, potentially contributing to arterial calcification.
Better Together
The D3 + K2 combination is one of the most evidence-backed supplement pairings. D3 ensures you absorb enough calcium; K2 ensures that calcium is deposited where it helps (bones) rather than where it harms (arteries). This is why most high-quality D3 supplements now include K2.
Side-by-Side Comparison
Primary Role
Vitamin D3
Calcium absorption, immune function, mood
Vitamin K2 (MK-7)
Directs calcium to bones, away from arteries
Deficiency Risk
Vitamin D3
Very high — ~42% of US adults are deficient
Vitamin K2 (MK-7)
Moderate — less tested but widespread sub-optimal intake
Solo Supplementation
Vitamin D3
Safe alone at moderate doses (1,000–2,000 IU)
Vitamin K2 (MK-7)
Safe alone, but most beneficial paired with D3
Synergy
Vitamin D3
Enhanced by K2 — prevents calcium misplacement
Vitamin K2 (MK-7)
Enhanced by D3 — more calcium to direct
Food Sources
Vitamin D3
Sunlight, fatty fish, fortified foods
Vitamin K2 (MK-7)
Natto, hard cheeses, egg yolks (small amounts)
Our Verdict
These aren't competitors — they're teammates. If you supplement D3, add K2 (MK-7) to ensure calcium goes where it belongs. A combined D3+K2 supplement is the most practical approach.