Quick Verdict
Caffeine
Most consumed psychoactive. Adenosine antagonist. Well-established ergogenic aid across nearly all exercise modalities.
Evidence: strong (1300+ studies)
Vitamin D3
Actually a steroid hormone precursor. Critical for calcium absorption, immune function, hormone production. Widespread d
Evidence: strong (1000+ studies)
Side-by-Side Comparison
| Caffeine | Vitamin D3 | |
|---|---|---|
| Category | performance | vitamins |
| Evidence Level | strong | strong |
| Studies | 1300+ | 1000+ |
| Dosage | 3-6 mg/kg | 1000-5000 IU |
Stack Compatibility
Caffeine: L-theanine (1:2 ratio caffeine:theanine), Creatine, Tyrosine
Vitamin D3: Magnesium (essential cofactor), Vitamin K2 (MK-7), Calcium (if dietary intake low), Zinc
Which Should You Choose?
Both serve different purposes. Choose based on your priority.