Vitamin D3
Also known as: cholecalciferol, vitamin D, D3, colecalciferol
Effective Dosage
400–80,000 IU daily depending on condition and deficiency status
What the Science Says
Vitamin D3 (cholecalciferol) is the form of vitamin D your body makes from sunlight and the form most commonly used in supplements. The provided studies show it can improve exercise tolerance and reduce fatigue in people with COPD who are deficient, support immune regulation in children with food allergies, and may offer neuroprotective effects when combined with anti-seizure medications in animal models. It also appears to play a role in bone health when combined with calcium, and exploratory cancer research suggests it may reduce relapse risk in digestive tract cancer patients with mid-range vitamin A levels.
What It Doesn't Do
Won't improve bone density or reduce fractures on its own in healthy adults — the large VITAL trial found no fracture benefit from supplementation. Not a standalone treatment for anxiety, epilepsy, or cancer. Won't build muscle or boost neurotransmitters directly. No evidence it benefits people who are already vitamin D sufficient. Not proven to improve lung function (FEV1/FVC) in COPD patients, only exercise tolerance.
Evidence-Based Benefits
Vitamin D3 supplementation in deficient COPD patients significantly improved exercise tolerance, dyspnea, and fatigue scores over 26 weeks compared to placebo (PMID: 41914100). In a pediatric CMA trial, D3 as part of a multicomponent supplement improved serum 25(OH)D levels, body growth, and immune tolerance markers including reduced Th2 cytokines and increased IL-10 and Treg activity (PMID: 41918962). In a post-hoc cancer RCT analysis, D3 supplementation was associated with improved relapse-free survival in digestive tract cancer patients with middle-to-upper range serum vitamin A levels (PMID: 41524587). Animal studies suggest neuroprotective effects when combined with antiseizure medications, reducing seizure severity and hippocampal neurodegeneration (PMID: 41766232).
Moderate EvidenceEffective at: No established dose from provided studies alone; study doses ranged from 400 IU/day to 80,000 IU/week
Source: auto-research
Absorption & Bioavailability
Good — D3 is a fat-soluble vitamin absorbed well with dietary fat. Serum 25(OH)D levels measurably increase with supplementation across multiple provided studies, confirming reliable absorption.
Red Flags to Watch For
- High-dose regimens (e.g., 80,000 IU/week) used in clinical trials should not be self-administered without medical supervision — vitamin D toxicity is possible
- Most benefits in the provided studies were seen in people who were already deficient; supplementing when levels are normal may provide little to no benefit
- Several provided studies used D3 as part of a multi-ingredient supplement (with DHA, prebiotics, calcium, NAC), making it impossible to isolate D3's specific contribution
- Animal feed analysis and computational docking studies (ALS/TDP-43) in this dataset are not human clinical evidence — do not interpret these as proven human benefits
Products Containing Vitamin D3
See how Vitamin D3 is used in these analyzed products:
Research Sources
- PubMed
- NIH DSLD
This information is for educational purposes only and is not medical advice. Always consult a healthcare professional before starting any supplement regimen. Last updated: 2026-04-06