Sports Research Vitamin D3 5,000 IU + K2 Review

Yes, for once-daily dosing protocols. MK-7 has a 72-hour serum half-life versus MK-4's 1-2 hours — so a single 100 mcg cap maintains steady-state matrix-Gla-protein (MGP) activation across the full 24-hour cycle, while MK-4 requires multiple daily doses to hold the same MGP carboxylation. For the cardiovascular calcium-direction protection use case (the primary reason most buyers add K2 to their D3 protocol), MK-7 is the more practical form. Thorne's MK-4 has more bone-specific clinical-trial data (Japanese osteoporosis trials used 45 mg/day MK-4), but at the 100-200 mcg dose range Sports Research uses, MK-7 wins on both pharmacokinetics and once-daily adherence.

First, we could not confirm this bottle's listing. The brand states Informed Sport; sport.wetestyoutrust.com blocks automated lookups, so check the batch there before buying. Informed Sport (UK-based, run by LGC Group) tests batches against WADA-prohibited substances and is accepted by most international federations (IAAF, UEFA, FIFA), most Olympic federations, and most non-US drug-tested contexts. But US-league athletes (NCAA, MLB, NFL, NHL, MLS) specifically require NSF Certified for Sport — Informed Sport isn't on those leagues' approved-certification lists. If you compete in any of those US leagues, pick a product listed at nsfsport.com (Thorne D-5,000 is listed there; Thorne D + K2 Liquid is not).

K2 (especially MK-7) is light-sensitive and gradually degrades over long shelf life. A 60-softgel bottle turns over in ~2 months at one cap daily, which keeps K2 freshness high across the whole bottle. NOW Foods can ship a 240-cap D3-only bottle because cholecalciferol is more stable than K2 MK-7. The trade-off is more frequent re-orders — a minor adherence headwind that costs about 5 minutes every two months. For the formulation integrity, the smaller bottle is the right call.

No — the softgel base is coconut oil, and the carrier oil is in direct contact with the active ingredients. For coconut-allergic or coconut-sensitive buyers, this SKU is not appropriate. Switch to Pure Encapsulations Vitamin D3 5000 IU (#2) — clinician-grade hypoallergenic capsule with zero excipients — and pair a separate K2 MK-7 bottle from a non-coconut source. The unbundled stack costs about the same total monthly ($8-10) and avoids the allergen entirely.

Probably yes for steady-state maintenance. The Heaney 2003 dose-response math (~+1 ng/mL per 100 IU/day chronic) means 5,000 IU/day moves someone starting at 35 ng/mL to roughly 85 ng/mL over 8-12 weeks — overshooting the Pludowski 2018 40-60 ng/mL target band. The correct protocol on Sports Research: confirm deficiency on a blood test, run 5,000 IU/day for 8-12 weeks for active repletion, retest serum 25(OH)D, then drop to alternate-day or half-cap dosing if you're at the top of the target band. If you're not deficient at baseline, Nordic Naturals D3 1,000 IU (#7) is the better calibration.

It's calibrated for active repletion dosing rather than long-term maintenance. The Knapen 2013 MK-7 RCT used 180 mcg/day to reduce bone loss in postmenopausal women, so 100 mcg/day is in the lower-effective range — enough for MGP activation across the population most buyers fall into. If you're a postmenopausal woman specifically targeting bone-density outcomes or you have known vascular calcification risk factors, consider adding a separate 100 mcg MK-7 bottle for a total ~200 mcg/day. For everyone else, the 100 mcg per softgel is calibrated correctly.

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 showing D3 raised serum 25(OH)D ~1.7× more efficiently than D2 at equivalent IU. The reason Sports Research uses cholecalciferol rather than ergocalciferol in this SKU.
2. [2] Pludowski 2018 PMID 28216084 — Vitamin D supplementation guidelines. Global expert consensus codifying the K2 + magnesium cofactor pairing for chronic D3 dosing and the 40-60 ng/mL serum 25(OH)D target band. The reference protocol that justifies Sports Research's D + K bundled formulation as evidence-based.
3. [3] Heaney 2003 PMID 12499343 — Human serum 25-hydroxycholecalciferol response to extended oral dosing with cholecalciferol. Dose-response rule: chronic oral D3 raises serum 25(OH)D by approximately +1 ng/mL per +100 IU/day, with diminishing returns past 40 ng/mL. Maps directly onto Sports Research's 5,000 IU/day dose targeting active repletion in deficient subjects.
4. [4] Knapen 2013 PMID 23525894 — Three-year low-dose menaquinone-7 supplementation helps decrease bone loss in healthy postmenopausal women. 3-year RCT in 244 postmenopausal women: 180 mcg/day MK-7 reduced age-related bone loss vs placebo, mediated by improved osteocalcin carboxylation. The reference trial for MK-7 dose-response — the 100 mcg/day Sports Research dose is in the lower-effective range and works synergistically with D3.
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 male buyers should dose Sports Research at the full 5,000 IU/day rather than a half-cap maintenance level.