Bioavailability of Zinc Bisglycinate
Zinc bisglycinate demonstrates superior bioavailability compared to most other zinc formulations, with approximately 43% higher absorption than zinc gluconate and substantially better absorption than inorganic zinc salts like zinc sulfate. 1
Comparative Absorption Data
The most direct evidence comes from a randomized crossover study in healthy volunteers showing that zinc bis-glycinate increased oral bioavailability by 43.4% compared to zinc gluconate when both were administered at 15 mg doses. 1 This study used validated ICP-OES methodology to measure serum zinc concentrations and calculated areas-under-the-curve (AUCs) to determine bioavailability differences. 1
Among organic zinc compounds, zinc bisglycinate (also called zinc glycinate) and zinc gluconate consistently demonstrate the highest absorption rates in clinical studies. 2, 3 A 2024 narrative review of clinical evidence concluded that zinc glycinate and zinc gluconate are better absorbed than other chemical forms of zinc in humans. 3
Mechanism of Enhanced Absorption
The FDA drug label for citrated zinc bisglycinate explains that this formulation consists of zinc chelated by glycine in the presence of citric acid, and this chelated form has been shown to have improved absorption over inorganic zinc salts such as zinc sulfate. 4 Once absorbed, the zinc is released from the chelate, with glycine utilized in normal protein metabolism and zinc bound to albumin and distributed throughout the body. 4
Clinical Performance Comparison
A 6-week intervention study in young adult women compared 60 mg/day of zinc glycinate versus zinc gluconate. Plasma zinc levels increased significantly in all subjects given zinc glycinate (N=10), while no significant change was seen overall for zinc gluconate or placebo groups. 5 This demonstrates that zinc glycinate more effectively changes zinc status than zinc gluconate under these conditions. 5
However, one study showed that tableted zinc formulations may have reduced bioavailability compared to aqueous solutions. The relative bioavailability of oral zinc from NutriSet tablets was only about half that of aqueous zinc sulfate, as indicated by area under the curve measurements. 6 This suggests that formulation and delivery method matter beyond just the chemical form of zinc.
Practical Implications
ESPEN guidelines specifically recommend organic zinc compounds (zinc gluconate, zinc citrate, zinc orotate, zinc histidinate) as superior to inorganic forms (zinc sulfate, zinc chloride, zinc oxide), with zinc gluconate and zinc glycinate demonstrating the highest absorption rates. 2 The guidelines note that zinc orotate is specifically recommended for better tolerability than inorganic salts. 2
For optimal absorption, zinc should be taken 30 minutes before meals, as food interferes with zinc uptake. 2, 7 For therapeutic doses ≥75 mg daily, dividing into at least twice-daily dosing prevents transporter saturation. 2, 7
Important Caveats
While zinc bisglycinate has superior bioavailability, this does not eliminate the risk of zinc-induced copper deficiency. All zinc formulations block copper absorption through the identical mechanism of inducing enterocyte metallothionein, regardless of the zinc salt used. 8 The European Association for the Study of the Liver explicitly states that the zinc salt does not make a difference with respect to copper-blocking efficacy, only tolerability. 8
The recommended zinc:copper ratio is 8-15:1 to avoid zinc-induced copper deficiency, and monitoring both zinc and copper levels every 6-12 months is advised for those taking supplemental zinc. 8