Biochemical dynamics of micronutrients

Mechanism

Mechanisms of Synergy and Luminal Interference

Micronutrients interact competitively or facilitatively in the intestinal lumen before cellular absorption:

• Chemical synergism: Ascorbic acid (Vitamin C) acts as a reducing agent, converting non-absorbable ferric iron (Fe³⁺) into soluble ferrous iron (Fe²⁺), facilitating its binding to the divalent metal transporter type 1 (DMT1).
• Competitive antagonism: Divalent cations with similar ionic radii, such as zinc (Zn²⁺), calcium (Ca²⁺) and copper (Cu²⁺), compete directly for the same apical membrane transporters, so that excessive supplementation of one of them can induce secondary deficiency of the others.

Coenzymes and epigenetic control

A significant fraction of the water-soluble vitamins of the B complex undergo obligatory intracellular transformations to become active coenzymes. These modified molecules bind covalently or transiently to the apoenzymes to constitute the catalytically active holoenzyme. On the other hand, fat-soluble vitamins such as vitamin A and vitamin D act in a manner analogous to steroid hormones, binding to specific nuclear receptors (such as RAR, RXR and VDR) to regulate gene transcription and coordinate processes of differentiation, immunomodulation and cellular mineral homeostasis.

Pharmacokinetics

Kinetics of transport and absorption of micronutrients

Unlike macronutrients, which are absorbed in large quantities through mass transport mechanisms or extensive enzymatic digestion, the uptake of vitamins and minerals is regulated by specific transport systems in the intestinal mucosa, subject to physiological feedback and kinetic saturation limits. Nutrient transport in the enterocyte follows saturation kinetic models described by the Michaelis-Menten equation:

Where v represents the speed of active transport and [S] the concentration of the micronutrient in the intestinal lumen. At low or normal physiological concentrations, facilitated or active primary/secondary transport dependent on ionic gradients (e.g., sodium) predominates. At high pharmacological concentrations (megadoses of supplementation), active transport mechanisms become saturated and residual absorption occurs non-specifically through paracellular passive diffusion, whose percentage efficiency rate is substantially lower.