Comparison
Ashwagandha vs Vitamin D3 + K2
Side-by-side of Ashwagandha and Vitamin D3 + K2. Every row below is pulled from the compound schema and will update as our data grows. For deeper reads, follow through to each compound page.
Ashwagandha
Ashwagandha supplement guide: KSM-66 and Sensoril extracts at 300-600 mg/day cut morning cortisol and stress in RCTs. Dose, side effects, testosterone data.
Vitamin D3 + K2
Vitamin D3 K2 supplement profile: cholecalciferol at 1000-4000 IU/day corrects deficiency, MK-7 directs calcium to bone, away from arteries.
Effects at a glance
Ashwagandha
- •Reduces morning serum cortisol by ~20 to 30% at 300 to 600 mg/day standardized extract over 8 weeks
- •Lowers subjective stress on DASS-21 and PSS scales versus placebo in chronically stressed adults
- •Modest grip-strength and 1-RM gains of ~5 to 8% in trained men when paired with resistance training
- •Improves self-reported sleep quality and onset latency in adults with insomnia symptoms
- •Small testosterone increases (~10 to 15%) reported in stressed or subfertile men, less clear in healthy populations
- •May raise free T3 and T4; can interact with levothyroxine and unmask subclinical hyperthyroidism
Vitamin D3 + K2
- •Reduces non-vertebral fractures 10-20% in older adults at 800 IU/day or above when combined with calcium
- •VITAL trial showed neutral results on primary CV and cancer endpoints at 2000 IU/day over 5 years
- •Vitamin D supplementation reduces respiratory infection incidence ~10-20% in deficient populations
- •K2 MK-7 has 72-hour plasma half-life vs 1-2 hours for MK-4; once-daily dosing is sufficient
- •Synergy hypothesis is largely preclinical; dedicated combination RCTs are limited
- •Daily dosing outperforms bolus dosing for immune and infection outcomes
Side-by-side
| Attribute | Ashwagandha | Vitamin D3 + K2 |
|---|---|---|
| Category | natural | supplement |
| Also known as | Withania somnifera, KSM-66, Sensoril | cholecalciferol + menaquinone, D3/K2, vitamin D3 with MK-7 |
| Half-life (hr) ↗ | 10 | 360 |
| Typical dose (mg) ↗ | 600 | 0.05 |
| Dosing frequency | daily | daily with a fat-containing meal |
| Routes | oral | oral |
| Onset (hr) | 2 | 24 |
| Peak (hr) | - | 168 |
| Molecular weight | - | 384.64 |
| Molecular formula | - | C27H44O (D3); C46H64O2 (MK-7) |
| Mechanism | GABAergic modulation and HPA-axis attenuation; withanolides reduce cortisol secretion and inhibit NF-kB signaling. | D3 converts to calcidiol then calcitriol, activating the vitamin D receptor (VDR) to increase intestinal calcium absorption and modulate immune and bone gene transcription. K2 carboxylates osteocalcin and matrix Gla protein, directing calcium toward bone and inhibiting vascular calcification. |
| Legal status | Dietary supplement in most jurisdictions; regulated in Denmark | Dietary supplement (global) |
| WADA status | allowed | allowed |
| DEA / Rx | OTC supplement | Not scheduled |
| Pregnancy | Not recommended | Recommended at standard doses for fetal bone development; consult clinician at higher doses |
| CAS | - | 67-97-0 |
| PubChem CID | - | 5280795 |
| Wikidata | Q310109 | Q139347 |
Safety profile
Ashwagandha
Common side effects
- mild GI upset
- drowsiness
- headache
Contraindications
- pregnancy
- autoimmune disease (theoretical immune stimulation)
- hyperthyroidism
- concurrent sedative use
Interactions
- benzodiazepines: additive CNS depression(moderate)
- thyroid hormone (levothyroxine): may raise T3/T4, altering dose requirements(moderate)
- immunosuppressants: theoretical antagonism via immune stimulation(moderate)
Vitamin D3 + K2
Common side effects
- GI upset at high doses
- headache (rare)
- hypercalcemia (only at sustained very high D3 doses)
Contraindications
- hypercalcemia
- sarcoidosis
- active hyperparathyroidism
- warfarin therapy (K2 component requires stable intake)
Interactions
- warfarin: K2 component can affect anticoagulation; maintain stable intake and inform anticoagulation clinic(moderate)
- thiazide diuretics: additive calcium retention; hypercalcemia risk with high-dose D3(moderate)
- digoxin and calcium channel blockers: additive effects from D3-induced hypercalcemia(moderate)
- glucocorticoids: reduced vitamin D efficacy and bone effects(moderate)
- cholestyramine and orlistat: bind fat-soluble vitamins; separate dosing by 2 to 4 hours(moderate)
Which Should You Take?
Vitamin D3 + K2 comes out ahead for most readers on the criteria we weight: 3 catalogued goals, OTC dietary supplement, oral dosing, with a Tier-A outcome catalogued. Ashwagandha is the right call when one of the conditionals below applies.
- → If your priority is stress and HPA-axis regulation, pick Ashwagandha.
- → If your priority is focus or working memory, pick Ashwagandha.
- → If your priority is bone density, pick Vitamin D3 + K2.
- → If your priority is healthspan extension, pick Vitamin D3 + K2.
Edge case: Half-lives differ materially (Ashwagandha ~10 hr vs Vitamin D3 + K2 ~360 hr). Vitamin D3 + K2 reaches steady state faster; Ashwagandha is easier to dial in if tolerability is uncertain.
Default choice: Vitamin D3 + K2. Lower friction to source, a Tier-A evidence outcome catalogued, and broader goal coverage. Reach for Ashwagandha only if your priority sits squarely in the goals it owns above.
This verdict is generated from each compound's schema (goals, legal status, evidence outcomes, dosing route). It updates automatically as our compound data evolves; the deeper read sits on each individual compound page.
Common questions
What is the difference between Ashwagandha and Vitamin D3 + K2?
Ashwagandha and Vitamin D3 + K2 differ in category (natural vs supplement), mechanism, and typical dosing. See the side-by-side table for full details.
Which has a longer half-life, Ashwagandha or Vitamin D3 + K2?
Ashwagandha half-life is 10 hours; Vitamin D3 + K2 half-life is 360 hours.
Can you stack Ashwagandha with Vitamin D3 + K2?
Stack compatibility depends on mechanism overlap, legal status, and individual response. Check each compound page for specific interactions and contraindications before combining.
Go deeper