A concentrated grass-fed butterfat that delivers vitamins A, D, and K2, valued as a whole-food way to support bone and heart health. The oil itself has never been tested in a controlled trial, so its benefits are plausible but unproven. Sensible use hinges on tracking total vitamin A and D intake and on product quality. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum retinol (vitamin A) | ~1.0–2.5 µmol/L (~30–70 µg/dL) | Detects deficiency to correct and excess to avoid |
| 25-hydroxy vitamin D | ~30–50 ng/mL (75–125 nmol/L) | Tracks vitamin D status and guards against excess |
| Undercarboxylated osteocalcin | Lower is better | Sensitive marker of vitamin K adequacy for bone |
| PIVKA-II | Undetectable / low | Marker of overall vitamin K sufficiency |
| Serum calcium | ~8.6–10.0 mg/dL | Screens for vitamin-D-related excess calcium |
| INR (international normalized ratio) | Per anticoagulation target (e.g., 2.0–3.0) | Detects loss of anticoagulant control from vitamin K |
Cadence: Re-check vitamin A and D at about 3 months after starting or changing dose, then every 6–12 months with long-term use; check clotting measures within 1–2 weeks of any change for those on anticoagulants.