Vitamin D3
Essential for bone, immunity, and testosterone synthesis. Most Japanese adults run low due to indoor life and sunscreen; dosing ideally follows a blood test.
Typical dose
2,000–5,000 IU per day
Timing
With a fatty meal — easiest after breakfast
Monthly cost (approx.)
~$3
Primary goals
health · performance · recovery
Scientific Evidence
Papers Forgestack cites for Vitamin D3 recommendations. Each link goes to PubMed or an official society source.
- Meta-AnalysisTier 1
Farrokhyar et al. 2017 · PubMed / Source
- GuidelineTier 1
Holick et al. 2011 · PubMed / Source
- Meta-AnalysisTier 1
Martineau et al. 2017 · PubMed / Source
- ReviewTier 2
Dahlquist et al. 2015 · PubMed / Source
- Safety EvidenceTier 1Safety
Institute of Medicine 2011 · PubMed / Source
Side Effects & Cautions
- rare
Hypercalcaemia with chronic high-dose use (>10,000 IU/day)
- rare
Risk of kidney calcification above the 4,000 IU/day upper limit
Consult a physician or pharmacist if in doubt. Forgestack does not provide medical advice.
Interactions
Thiazide diuretics
May amplify rises in blood calcium.
Separate calcium supplements
Stacking at high doses increases hypercalcaemia risk.
Where to Buy
The links below are affiliate links. Your price does not change.
Whether this supplement should be your top priority depends on your goal and current stack.