Thorne Vitamin D + K2 Liquid Review

No. nsfsport.com lists other Thorne products (Thorne D-5,000 among them) but not Vitamin D + K2 (checked Oct 6, 2026). The bottle is NSF contents-certified under NSF/ANSI 173, which verifies label contents and screens contaminants; that is not banned-substance testing. Drug-tested athletes should pick a product listed at nsfsport.com (Thorne D-5,000 is listed there). For everyone else, NOW Foods ships the same D3 cholecalciferol molecule at $3/month with no functional difference at the VDR or muscle level. The premium here buys the K2 stack, the drop format and the certified label.

MK-4 has more direct clinical-trial data on bone outcomes (Japanese osteoporosis trials used 45 mg/day MK-4) — Thorne's choice reflects clinical-research lineage. But for everyday cardiovascular calcium-direction insurance, MK-7's 72-hour half-life is more practical for once-daily dosing than MK-4's 1-2 hour half-life. If you specifically want MK-7, Sports Research D3+K2 (#4) is the better K2 form for chronic cardio protection. Thorne's MK-4 still works at 200 mcg/serving — you just may want to split into 2 daily doses for steady-state matrix-Gla-protein activation.

10 drops/day during the 8-12 week loading phase — that's 5,000 IU D3 + 1,000 mcg K2 MK-4. The Heaney 2003 dose-response math says +1 ng/mL per 100 IU/day, so 10 drops moves a 15 ng/mL subject to 65 ng/mL over 12 weeks. At that load, the 1 oz bottle lasts about 60 days and monthly cost climbs to ~$55. After 12 weeks, retest serum 25(OH)D; if you're in the 40-60 ng/mL target band, drop to 2-4 drops/day for maintenance. For pure loading-phase math, Sports Research D3+K2 at $11/month is the better cost-per-IU choice.

The MCT-oil base partially compensates for empty-stomach dosing — fat-soluble D3 absorption is supported by the carrier oil itself. But the literature still favours co-ingested dietary fat for full absorption. Practical protocol: add 2 drops to morning coffee with cream, a smoothie with avocado or nut butter, or any meal containing at least 10g of fat. Plain water dosing works but loses ~20-30% absorption versus food. Time of day doesn't matter much — pick whatever sticks for adherence.

Less dramatically than fish oil but yes — MCT oil oxidises slowly over months once the dropper is opened to air. Thorne recommends finishing within 90 days of first opening for full potency. The 1 oz bottle is sized to last 60-150 days at typical doses, so most users finish before oxidation becomes meaningful. Store in a cool dark place (not the bathroom counter where humidity + light accelerate degradation). If the oil smells rancid or tastes sharply bitter, replace the bottle.

Documented and verifiable — Thorne is the official sports-supplement partner of UFC and CrossFit and supplies multiple US Olympic teams, and several Thorne products are on the NSF Certified for Sport list. This D + K2 liquid is not one of them (nsfsport.com, checked Oct 6, 2026). Mayo Clinic and Cleveland Clinic also have partnerships. Those partnerships are brand trust, not a certification of this bottle. Tested athletes should pick a product listed at nsfsport.com (Thorne D-5,000 is listed there).

1. [1] Tripkovic 2012 PMID 22552031 — Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Pooled meta-analysis of 7 head-to-head D2-vs-D3 RCTs: D3 raised serum 25(OH)D ~1.7× more efficiently than D2 at equivalent oral doses. The reference paper that drove the consumer supplement industry's convergence on cholecalciferol — the form Thorne uses in this bottle.
2. [2] Pludowski 2018 PMID 28216084 — Vitamin D supplementation guidelines. Global expert-consensus document codifying the K2 + magnesium cofactor pairing for D3 supplementation, the 40-60 ng/mL serum 25(OH)D target band, and dosing by deficiency severity. The reference protocol that justifies Thorne's D + K co-formulation as evidence-based rather than marketing-driven.
3. [3] Heaney 2003 PMID 12499343 — Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Established the dose-response rule of approximately +1 ng/mL serum 25(OH)D per 100 IU/day chronic D3 dosing. Maps directly onto why Thorne's 1,000 IU/2-drop maintenance dose works for sufficient subjects but requires higher dosing (5,000 IU/10 drops) for active repletion.
4. [4] Bischoff-Ferrari 2009 PMID 19797342 — Fall prevention with supplemental and active forms of vitamin D: a meta-analysis of randomised controlled trials. Meta-analysis of 8 RCTs (n=2,426) showed 700-1,000 IU/day vitamin D3 reduced fall incidence in adults 65+ by 19%, mediated by VDR-driven muscle + balance improvements. The endpoint Thorne's 1,000 IU/serving dose is specifically calibrated against for older athletes and clinical contexts.
5. [5] Pilz 2011 PMID 21154195 — Effect of vitamin D supplementation on testosterone levels in men. RCT in 165 D-deficient overweight men: 3,332 IU/day D3 for 12 months produced +25% total testosterone, +20% bioactive T, +24% free T over placebo. The reference for why deficient men using this bottle should still dose at 6-7 drops/day (3,300+ IU) rather than the 2-drop maintenance default.