Final answer:
Calcium is the mineral that reduces the absorption of tetracycline, due to the formation of insoluble complexes that decrease tetracycline's effectiveness.
Step-by-step explanation:
The mineral that reduces the absorption of tetracycline when they are given together is calcium. Tetracycline, a natural antibiotic produced by soil bacteria and a polycyclic aromatic compound, inhibits bacterial protein synthesis by obstructing the bond of the transfer RNA-amino acid to the ribosome. The integration of calcium or other divalent cations with tetracycline forms insoluble complexes that are poorly absorbed from the gastrointestinal tract, resulting in a reduction in the drug's effectiveness. Hence, calcium supplements, dairy products, or foods high in calcium should be avoided or taken at a different time than tetracycline to prevent interactions.