Vitamin D3 is required for testosterone production, calcium metabolism, bone mineralization, hair follicle function, and immune regulation. Most peptide users — particularly TRT users and indoor lifestyle users — are deficient. Vitamin K2 directs calcium to bones rather than arteries (critical when supplementing higher D3 doses). The D3 + K2 combination is the foundational supplement for peptide-stack and TRT users.
The 5 picks
1. Best overall — Thorne Vitamin D/K2 Liquid
1,000 IU D3 + 200 mcg K2 per drop. Sublingual. ~$40 / 2 months.
Thorne® liquid D/K2 allows precise dosing (drops) and sublingual absorption. Most-recommended D3/K2 combo by functional medicine physicians.
Shop Thorne D/K2 on Amazon Prime →
2. Best practitioner-grade — Pure Encapsulations D3 + K2
1,000 IU D3 + 90 mcg K2 (MK-7). ~$30/month.
Pure Encapsulations® uses MK-7 form of K2 (most bioavailable). Hypoallergenic, third-party tested, practitioner-grade.
Shop Pure Encapsulations on Amazon Prime →
3. Best value — Sports Research Vitamin D3 + K2
5,000 IU D3 + 100 mcg K2 (MK-7). Coconut oil base. ~$15/month.
Sports Research® delivers therapeutic-dose D3 + premium K2 form at the best value. 1/3 the price of practitioner brands.
Shop Sports Research D3 on Amazon Prime →
4. Best comprehensive — Designs for Health DK Multi
5,000 IU D3 + 1,000 mcg K2 (MK-4 + MK-7 blend). ~$45/month.
Designs for Health® uses both MK-4 and MK-7 K2 forms for complementary absorption profiles. Highest K2 content in this list.
Shop Designs for Health on Amazon Prime →
5. Best high-dose — Carlson Labs Super Daily D3+K2
5,000 IU D3 + 90 mcg K2. Liquid drops. ~$25 / 2 months.
Carlson Labs® liquid D3+K2 drops allow easy dose adjustment. Drops form lets you titrate up if labs show severe deficiency.
Shop Carlson D3+K2 on Amazon Prime →
Pair with peptide stack
- Vial Vault Pro Max — organizes the full peptide stack.
- TempView — keeps peptides at 4 °C storage spec.
Related
Affiliate disclosure: VialCase is a participant in the Amazon Services LLC Associates Program. As an Amazon Associate, VialCase earns from qualifying purchases at no additional cost to you. Trademarks: Thorne®, Pure Encapsulations®, Sports Research®, Designs for Health®, Carlson Labs®, Ozempic®, Wegovy®, Mounjaro®, Zepbound® are registered trademarks of their respective owners. VialCase is not affiliated with, endorsed by, or sponsored by these brands.
Frequently Asked Questions
How much D3 should peptide / TRT users take?
Most adults need 2,000-5,000 IU daily. Get a blood test first; target 50-80 ng/mL serum 25(OH)D. Some users need 10,000 IU daily for several weeks to correct deficiency.
Why pair D3 with K2?
D3 increases calcium absorption. K2 directs that calcium to bones (not arteries). Taking high-dose D3 without K2 can theoretically increase arterial calcification — pairing them is the safer protocol.
MK-4 vs MK-7 K2?
MK-7 has longer half-life and is more bioavailable per dose. MK-4 is what your body normally produces. Many premium products use both forms for combined benefit.
Will D3 raise testosterone?
For deficient users — yes, modestly. Vitamin D is a cofactor for testosterone synthesis. For non-deficient users, additional D3 doesn't raise testosterone further.
Can I overdose on D3?
Above 10,000 IU daily long-term, yes. Toxicity symptoms: hypercalcemia, kidney damage. Stick to 2,000-5,000 IU for maintenance; only go higher under physician supervision with labs.
Safe with my GLP-1?
Yes — no interaction. Take with the largest meal of the day for fat-soluble vitamin absorption.
Educational only. Confirm protocols with your prescribing healthcare provider.
