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Head-to-head evidence comparison — which supplement is right for you?
Vitamin D3 wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
6 of 8 studies with measurable effects showed benefit.
Top outcomes
Verdict
Probably helps
18 of 30 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (2)
Outcomes where both L-Lysine and Vitamin D3 have evidence — compare verdict strength side-by-side.
500-3000mg daily; higher for active outbreaks
Empty stomach for better absorption, Divided doses throughout day, Away from high-arginine foods
L-Lysine HCl (capsules or powder)
2000-4000 IU daily
Morning with breakfast
D3 (cholecalciferol) softgel or liquid
2-4 weeks prevention; acute treatment faster
4-8 weeks
Ongoing
4-8 weeks
4-8 weeks
2-4 weeks
4-8 weeks
The Impact of Amino Acids on Postprandial Glucose and Insulin Kinetics in Humans: A Quantitative Overview
Nutrients (2020) · Systematic review · n=55
Oral ingestion of most individual AAs induced an insulin response, but did not alter glucose concentrations in healthy participants.
Nutraceuticals and phytoceuticals in the treatment of schizophrenia: a systematic review and network meta-analysis "Nutra NMA SCZ"
Molecular psychiatry (2025) · Meta analysis · n=50
Change (Standardized Mean Difference = SMD) in total symptomatology and acceptability (Risk Ratio = RR) were co-primary outcomes.
A Dietary Supplement in the Management of Patients with Lumbar Osteochondrosis: A Randomized, Double-Blinded, Placebo-Controlled Study
Nutrients (2024) · Rct
Despite no significance regarding the distribution of Pfirrmann grade changes (improvement, no change, worsening; p = 0.259), in the supplement group, one patient achieved a three-grade improvement, and worsening of Pfirrmann grades were only detected in the placebo group (9.1%).
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
Safety profile based on systematic review of 71 studies (n=2619). Risk analysis showed no statistically significant increase in GI symptoms (RR 1.02, 95% CI 0.96-1.07, p=0.49). Adverse events were mainly subjective GI symptoms. Short-term use up to 6g appears safe.
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.
Vitamin D3 has a higher evidence score (7.5/10 vs 5.5/10) and wins in 2 of 3 categories.
For support immune system, Vitamin D3 has a higher relevance score (92 vs 70).
No known interactions between L-Lysine and Vitamin D3 have been documented in our database. However, always consult a healthcare provider before combining supplements.