A controlled absorption study using dual-isotope tracer methodology reveals a dramatic decline in zinc bioavailability across escalating doses. At 2mg, fractional absorption reaches 73%, but this plummets to 37% at 30mg—a 50% absolute reduction in absorption efficiency.
The physiological ceiling for net zinc absorption remains approximately 11mg per dose, determined by saturation of the ZIP4 transporter on intestinal enterocytes. Even modest dose escalations from 20mg to 30mg yield negligible gains, adding only 0.2mg of additional absorbed zinc. These findings, derived from a study of eight healthy adults receiving aqueous zinc sulfate, challenge conventional marketing assumptions that position higher-dose supplements as more effective.
The saturation phenomenon extends beyond zinc, affecting other micronutrient transporters and raising questions about the efficacy of megadose supplementation across the micronutrient spectrum. Read the full article on GMJ Newsroom.
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