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Head-to-head evidence comparison — which supplement is right for you?
L-Glutamine and Vitamin D3 are closely matched across evidence, studies, and safety.
Verdict
Likely helps
3 of 3 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
15 of 26 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both L-Glutamine and Vitamin D3 have evidence — compare verdict strength side-by-side.
5-10g
Post-workout, Before bed, Or split throughout day
L-Glutamine powder
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
2-4 weeks
2-4 weeks
1-2 weeks
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
A Phase 3 Trial of l-Glutamine in Sickle Cell Disease
The New England journal of medicine (2018) · Rct · n=230
A total of 230 patients (age range, 5 to 58 years; 53.9% female) were randomly assigned, in a 2:1 ratio, to receive l-glutamine (152 patients) or placebo (78 patients).
What Is the Role of Nutritional Supplements in Support of Total Hip Replacement and Total Knee Replacement Surgeries? A Systematic Review
Nutrients (2018) · Systematic review
Amino acid supplementation is reported to reduce muscle atrophy and accelerate return of functional mobility.
Evidence and gaps in clinical outcomes of novel pharmacologic therapies for sickle cell disease: A systematic literature review highlighting insights from clinical trials and real-world studies
Blood reviews (2025) · Systematic review · n=97
A pivotal phase III study of l-glutamine showed that patients treated with l-glutamine had a 25 % reduction in pain crises and 33 % fewer hospital days compared to placebo. l-glutamine was generally well tolerated with minimal side effects.
Vitamin D supplementation vs. placebo and incident type 2 diabetes in an ancillary study of the randomized Vitamin D and Omega-3 Trial
Nature communications (2025) · Meta analysis · n=5205
Mean body mass index (BMI) was 27.5 kg/m2 (SD = 5.3), with 51% female and 17% Black race/ethnicity.
Vitamin D Supplementation for Patients with Dysmenorrhoea: A Meta-Analysis with Trial Sequential Analysis of Randomised Controlled Trials
Nutrients (2024) · Meta analysis · n=687
TSA revealed that the current RCTs provide sufficient information.
Vitamin D and respiratory tract infections
BMJ (2017) · Meta analysis · n=11321
12% reduction in respiratory infections overall
Based on RCT showing reduced URTI incidence in combat athletes (n=21) and enhanced IgA levels. Limited sample size and specific population studied. Effect may be primarily in high-stress/training conditions.
Meta-analysis showed 12% overall reduction in respiratory infections, with greater benefits in severely deficient individuals. Daily dosing more effective than bolus. Conservative estimate assumes most users not severely deficient.
AI-estimated from published studies. Interpret as directional guidance.
Both L-Glutamine and Vitamin D3 are closely matched — the best choice depends on your specific health goals.
For support immune system, Vitamin D3 has a higher relevance score (92 vs 70).
No known interactions between L-Glutamine and Vitamin D3 have been documented in our database. However, always consult a healthcare provider before combining supplements.