Key points
- The upper intake level is 40 mg per day for adults.
- Add about 1 mg copper per 15 mg zinc when dosing long term.
- Separate from iron, calcium and tetracycline antibiotics by 2 hours.
What zinc does
Zinc is a cofactor for more than 300 enzymes and structural component of over 2000 transcription factors. It is essential for immune cell development, wound healing, protein synthesis and taste perception.
Short-course zinc at 75 mg daily shortens the duration of the common cold in several trials, which is why it is popular for immune support. That dose is nearly twice the daily upper limit, which is exactly why duration matters.
The copper depletion problem
Zinc induces metallothionein inside intestinal cells. Metallothionein has a higher affinity for copper than for zinc, so it binds copper and holds it in the enterocyte. When that cell sheds, the copper leaves with it.
Sustained zinc supplementation above 40 mg per day has produced frank copper deficiency in case reports — anaemia that is unresponsive to iron, plus neuropathy and, in severe cases, myelopathy. This is entirely preventable.
The practical rule is 1 mg of copper for every 15 mg of zinc. Take them at different times of day, because they also compete for the same absorption pathway.
Timing and competition
Zinc competes with iron through DMT1 and with calcium through overlapping pathways. Separate zinc from iron and calcium by at least two hours.
Tetracycline and fluoroquinolone antibiotics chelate zinc in the gut, and the loss is mutual — both the mineral and the antibiotic absorb worse. Take the antibiotic two hours before or four to six hours after zinc.
Phytates in grains and fortified cereals chelate zinc. A chelated form such as zinc picolinate resists this binding better than zinc oxide.