Why is copper bisglycinate better than copper sulfate?
The short answer
Copper sulfate is an inorganic salt that dissociates in the stomach, leaving the copper ion exposed to competing reactions with phytates and other minerals, and it's more likely to irritate the GI tract. The bisglycinate chelate shields the copper ion through digestion, which is well-supported for tolerability. The absorption advantage is plausible and backed by animal data (a 2007 steer study found roughly 140–150% relative bioavailability versus copper sulfate), but head-to-head human trials are limited — so it's fair to say bisglycinate is gentler and likely better absorbed, without claiming a specific multiplier in humans.
Tolerability is the clearest difference
Once copper sulfate dissociates in the stomach, the free copper ion can directly irritate the gastric lining and react with food components, which is why it has a reputation for nausea and stomach upset at supplemental doses. Copper bisglycinate stays chelated through gastric transit, so most people tolerate it even on an empty stomach. This is the main reason most reputable brands moved away from copper sulfate.
Absorption: plausible, not proven in humans
The strongest data comes from animal research, where the chelated form outperformed copper sulfate, particularly when dietary inhibitors were present. Mechanistic reviews support the idea that chelation protects copper from competing reactions. But definitive human bioavailability comparisons are sparse, so be skeptical of specific claims like "three times better absorbed."
For the full comparison including cost and every copper form, read the article copper bisglycinate vs copper sulfate.
Sources
- Hansen et al. (2007). Bioavailability of copper from copper glycinate in steers. PubMed: 17911232 — pubmed.ncbi.nlm.nih.gov
- University of Virginia GI Nutrition — Copper Deficiency: Like a Bad Penny (2020) — med.virginia.edu
Related questions
Is copper glycinate the same as copper bisglycinate?
What is copper bisglycinate good for?
Copper bisglycinate vs copper sulfate (full article)