The Formula Is Not the Dose · Manganese, Vitamin D and the New Regulatory Mathematics of Infant Nutrition

On 2 November 2026, the US Food and Drug Administration published a proposed overhaul of selected infant-formula nutrient specifications, including the first federal maximum for manganese and substantial changes to iodine and vitamins A and D. The proposal exposes a problem that extends beyond numerical reformulation: a declared nutrient concentration is neither the infant's total exposure nor proof of physiological adequacy. Ingredient-derived minerals, reconstitution water, variable intake, nutrient chemical forms, manufacturing tolerances and shelf-life losses jointly determine the delivered dose. This article critically compares the proposed US framework with binding European Union requirements, Spain's enforcement environment and the distinct legal position of Great Britain and Northern Ireland. It examines the scientific limitations of manganese neurodevelopmental evidence, vitamin-D co-supplementation, retinol-equivalent calculations and the constraints of soy-protein matrices. A proposed, explicitly unvalidated source-to-serving qualification model connects analytical chemistry, exposure assessment and robust formulation design. The central conclusion is that infant nutrition requires an auditable exposure system, not merely a compliant label.