Which form of zinc is best to take?

Zinc picolinate was the only form of zinc that, in a crossover study of 15 people, showed measurable increases in hair, urine and red blood cells after four weeks. Zinc gluconate and zinc citrate showed no measurable change compared to placebo at the same dose. This was a small study, but the outcome was statistically clear.

Zinc bound to the amino acid histidine also performs well. In a study of 10 volunteers, 15 mg of zinc histidine produced the same effect on blood zinc concentration as 45 mg of zinc sulfate. That is a substantial difference: you need three times less of it. Zinc aspartate outperformed zinc gluconate in a small crossover study of 8 people, and zinc gluconate outperformed zinc sulfate.

Zinc gluconate is in turn more readily absorbed by the body than zinc oxide: in a study of 12 men, the peak blood concentration was approximately 18% higher and total exposure approximately 8% higher. Zinc oxide and zinc sulfate perform equally well when incorporated into fortified foods, but as a standalone supplement zinc oxide clearly scores worse than gluconate.

Whatever you take: phytate in whole grains, maize and rice strongly blocks zinc absorption. This has been well demonstrated in multiple studies. It is therefore preferable to take zinc on an empty stomach, or to avoid combining it with large portions of grains or legumes. Fermenting, sprouting or enzymatically processing those foods considerably reduces that blocking effect.

A caveat: a review that identifies zinc glycinate and zinc gluconate as the best options was written by employees of a supplement manufacturer. That conclusion should therefore be kept in perspective. Taken together, the independent clinical studies point most strongly to zinc picolinate and zinc histidine as well-absorbed forms, though each study involved no more than 15 participants.