Where to Actually Get Vitamin D3 and K2 — From Supplements to Fermented Cod Liver Oil

We’ve written about why D3 and K2 work as a system. This post is about where to actually get them — and why the source matters more than most people realize.

The standard answer is a D3/K2 softgel. That’s a fine answer. But it’s not the complete picture. The ancestral nutrition tradition, the Weston A. Price research, and a growing body of food-based nutrient bioavailability data all point toward whole food sources that deliver both nutrients in forms the body has been processing for millennia — alongside cofactors that isolated supplements don’t include.

Here’s a practical breakdown of every meaningful source worth knowing about.

Standard Supplements: The Baseline

A quality D3/K2 softgel is the most reliable, dose-controllable option for most people. Look for:

• D3 as cholecalciferol — the animal-derived form identical to what skin synthesizes from UVB. Not D2 (ergocalciferol), which has lower potency and shorter half-life.
• K2 as MK-7 — the long-acting menaquinone form with the strongest evidence for vascular protection. At least 90mcg per serving; 180mcg if you’re on higher D3 doses.
• Oil-based delivery — softgels in olive or MCT oil. Both nutrients are fat-soluble and absorb poorly in dry powder capsules.
• Third-party tested — FCLO contamination scandals aside, supplement quality varies significantly. Look for COA documentation from NSF, USP, or Informed Sport.

Standard supplements are dependable and controllable. They’re also isolated — no cofactors, no synergistic nutrients, no food matrix. That’s fine for most people. But it’s not the only way.

Fermented Cod Liver Oil: The Ancestral Option

Fermented cod liver oil (FCLO) is one of the most nutrient-dense traditional foods ever documented. It was a staple of traditional Norwegian fishing communities, used medicinally for centuries, and elevated to nutritional prominence by Weston A. Price, who found it consistently present in the diets of the healthiest traditional populations he studied.

What makes FCLO distinct from standard cod liver oil:

Natural vitamin D: FCLO contains naturally occurring vitamin D3 in a food matrix alongside vitamin A, EPA, DHA, and fat-soluble activators. The D content varies by batch and manufacturer — this is both a feature (food-based, with cofactors) and a limitation (harder to dose precisely).

Natural vitamin K2 as MK-4: FCLO contains MK-4, the short-chain menaquinone form. MK-4 is the form found in animal tissues generally — brain, liver, eggs — and is the form the body converts from K1 via a UBIAD1-mediated pathway. It has a shorter half-life than MK-7 but is the form most prevalent in traditional diets.

The fermentation difference: Traditional fermentation preserves and concentrates fat-soluble nutrients without high-heat processing that can degrade them. Standard CLO is typically processed at high temperatures. The fermentation argument is compelling from a nutrient preservation standpoint, though head-to-head bioavailability data comparing fermented vs. standard CLO is limited.

Green Pasture is the primary commercial producer of FCLO in the US, and the brand most associated with the Weston A. Price community. Their Blue Ice fermented cod liver oil is the reference product in this category. Note that FCLO has a strong flavor profile — capsules are available but the oil form is traditional.

Practical consideration: FCLO is not a precision dosing tool. If you’re managing a specific vitamin D deficiency, standard supplements with tested doses are more reliable. FCLO works best as a whole-food foundation alongside targeted supplementation, or as a standalone option for people already maintaining adequate D levels through sun exposure.

Grass-Fed Butter Oil: K2 Concentrated

Butter oil — particularly from 100% grass-fed cows grazing on rapidly growing green grass — is one of the richest known food sources of vitamin K2 as MK-4. Weston A. Price called it “Activator X,” a fat-soluble nutrient he observed in the butterfat of traditionally grazed cattle that consistently correlated with skeletal and dental health in the populations he studied. We now understand Activator X to be primarily K2 MK-4.

The K2 content of butter fat is highly dependent on what the cow ate. Grain-fed dairy contains negligible K2. Grass-fed dairy — particularly from cows on fast-growing spring and summer pasture — contains meaningful amounts. Concentrated butter oil amplifies this further by removing the water and protein fractions.

Green Pasture also produces a X-Factor Gold High Vitamin Butter Oil specifically for this purpose. The traditional Weston A. Price protocol combined FCLO and butter oil as complementary fat-soluble nutrient sources — a synergy Price identified empirically before the mechanisms were understood.

Practical consideration: Grass-fed butter in meaningful daily amounts (2–4 tablespoons) from quality sources — Kerrygold, Anchor, or direct from a local grass-fed dairy — provides a dietary K2 baseline that supplements build on. It’s not a replacement for MK-7 supplementation in people with vascular calcification risk, but it’s a meaningful food-first contribution.

Other Meaningful Food Sources

Natto: The single highest food source of K2 by a significant margin — specifically MK-7, the long-acting form. A 3.5oz serving of natto contains roughly 1,000mcg of MK-7. The problem is that natto is a fermented soybean product with a flavor and texture profile that makes it essentially non-negotiable for most Western palates. If you eat it, you don’t need a K2 supplement. Most people don’t eat it.

Hard aged cheeses: Gouda, Brie, Edam, and Jarlsberg contain meaningful MK-7 and MK-4 from bacterial fermentation during aging. Gouda is often cited as the highest among common cheeses. Regular consumption of aged hard cheese provides a genuine dietary K2 contribution — not therapeutic doses, but a meaningful baseline.

Egg yolks (pasture-raised): Contain MK-4 in amounts that vary significantly based on the hen’s diet. Pasture-raised eggs from hens on green forage contain substantially more K2 than conventional eggs. Also a natural source of vitamin D3, again in amounts dependent on sun exposure and diet.

Liver (grass-fed beef or chicken): Rich in MK-4 alongside retinol, the natural form of vitamin A that works synergistically with D3 and K2 in the fat-soluble vitamin system. Traditional diets featuring regular organ meat consumption provided this entire fat-soluble complex together — the way Price observed it functioning in healthy traditional populations.

Sunlight: Still the Best D3 Source

No supplement or food source delivers vitamin D the way direct UVB exposure to skin does. Midday sun exposure on a significant body surface area — arms, legs, torso — for 15–30 minutes depending on skin tone and latitude can generate 10,000–20,000 IU of D3 in a single session, with no risk of toxicity because the body self-regulates production.

The problem is that most people living above 35° latitude from October through April cannot generate meaningful vitamin D from sunlight regardless of time spent outdoors — the UVB angle is too low. Supplementation fills this seasonal gap.

How to Think About This as a System

The most ancestrally coherent approach to D3 and K2 isn’t a single pill — it’s layered:

• Sunlight as the primary D3 source when geography and season allow
• Whole food sources — grass-fed dairy, pasture-raised eggs, liver, aged cheese — as a dietary K2 baseline
• FCLO and/or butter oil as traditional food-based concentrates for the Weston A. Price-aligned
• Targeted supplementation — D3 softgel + MK-7 K2 — to fill the gaps that food and sun can’t reliably cover

StaqWell is being built to help you understand which layers of this system you already have covered — and where the gaps are.

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Sources matter as much as doses — once you see the stack as layers, the protocol gets a lot clearer.