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Head-to-head evidence comparison — which supplement is right for you?
Zinc wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
6 of 6 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
21 of 26 studies with measurable effects showed benefit.
Top outcomes
3g before bed
30-60 minutes before bed
Powder (dissolves easily, tastes sweet)
15-30mg daily
With meals
Zinc picolinate or zinc citrate
First few nights
Next morning
Immediate
2-4 weeks
2-4 weeks
4-8 weeks
Immediate
The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
GeroScience (2024) · Systematic review · n=34
The nervous system demonstrated the most positive effects, including improved psychiatric symptoms from longer-term glycine administration in psychiatric populations.
Glutamatergic drugs for schizophrenia
The Cochrane database of systematic reviews (2006) · Meta analysis · n=132
NMDA receptor co-agonists glycine and D-serine showed some effects in reducing the negative symptoms of schizophrenia (n=132, SMD -0.66, CI -1.0 to -0.3, p=0.0004), but the magnitude of the effect was moderate.
Ingestion of a Whey Plus Collagen Protein Blend Increases Myofibrillar and Muscle Connective Protein Synthesis Rates
Medicine and science in sports and exercise (2025) · Rct · n=14
In addition, myofibrillar protein synthesis rates were higher in BLEND compared with PLA in both the rested (0.038 ± 0.008 and 0.031 ± 0.006%·h -1 , respectively; P < 0.05) and exercised (0.052 ± 0.011 and 0.039 ± 0.009%·h -1 , respectively; P < 0.01) leg.
Efficacy of Zinc Supplementation in the Management of Primary Dysmenorrhea: A Systematic Review and Meta-Analysis
Nutrients (2024) · Meta analysis · n=739
Zinc supplementation significantly reduced pain severity compared to placebo (Hedges's g = -1.541; 95% CI: -2.268 to -0.814; p < 0.001), representing a clinically meaningful reduction in pain.
Effects of Daily Zinc Alone or in Combination with Other Nutrient Supplements on the Risk of Malaria Parasitaemia: A Systematic Review and Meta-Analysis of Randomised Controlled Trials
Nutrients (2023) · Meta analysis · n=1339
The effect sizes, represented as risk ratios (RRs) with 95% confidence intervals (CIs), were standardised by transforming them into log RRs and then pooling them using a fixed-effects or random-effects model depending on the heterogeneity across studies.
Prevalence of Zinc Deficiency in Inflammatory Bowel Disease: A Systematic Review and Meta-Analysis
Nutrients (2022) · Meta analysis · n=806
Pooled analyses by the IBD subgroup showed a total population of 1677 with CD, for an overall mean zinc deficiency prevalence of 54% and 95% confidence intervals (CI) ranging from 0.51 to 0.56, versus 41% (95%CI 0.38-0.45) in the UC population (n = 806).
Based on systematic review showing nervous system benefits. Limited specific RCT data for sleep outcomes. Effects may vary significantly between individuals.
Based on meta-analyses showing reduced respiratory tract infections and improved immune markers (CD3/CD4). Effects primarily in deficient individuals. Take with food to reduce nausea risk.
AI-estimated from published studies. Interpret as directional guidance.
Zinc has a higher evidence score (8.5/10 vs 6.5/10) and wins in 2 of 3 categories.
For improve deep sleep quality, Glycine has a higher relevance score (95 vs 65).
No known interactions between Glycine and Zinc have been documented in our database. However, always consult a healthcare provider before combining supplements.