Which amino acid is considered conditionally essential in infancy?

• A. Arginine
• B. Cysteine
• C. Glycine
• D. Tryptophan

Answer: (A)

In infancy, some amino acids become conditionally essential because the body's ability to synthesize them is not yet fully mature. Arginine is one of the primary examples. Newborns, especially preterm infants, have an immature urea cycle, which limits their capacity to synthesize arginine from other precursors. Growth processes and the production of molecules like polyamines and nitric oxide rely on arginine, so the dietary supply becomes essential to meet those high needs during rapid development.

Breast milk and formula provide arginine to support this growth and metabolic demand. While cysteine can also be conditionally essential in infancy, and glycine is generally nonessential while tryptophan is essential for all ages, arginine is the classic nutrient highlighted as conditionally essential in infancy due to the immature synthesis capacity.