Human babies are extremely susceptible to acute nitrate poisoning due to certain bacteria that are present in their digestive systems at birth. Therefore, the level of oxygen being transported throughout the body decreases in proportion to the amount of hemoglobin that is converted to methemoglobin. As the oxygen level in the blood diminishes, the baby is suffocated. This condition is called methemoglobinemia. Infants are at greatest risk of developing methemoglobinemia from excessive intake of nitrate.
Fetal hemoglobin is in an immature form and is more readily oxidized than adult hemoglobin.
At birth, between 60 to 80 percent of the infant's hemoglobin remains in this immature form of the hemoglobin molecule, but by age three months, this decreases to approximately 30 percent By six months of age, an infant's digestive system is fully developed and none of the nitrate-converting bacteria appear to remain. Functionally, there is a deficiency of an enzyme or the enzyme's cofactor which inhibits the ability of hemoglobin to bind with iron. There is a decrease in the amount of hydrochloric acid in infants which may result in an overgrowth of nitrate-reducing bacteria in the upper gastrointestinal tract. The most obvious symptom of nitrate poisoning is a bluish coloration of the skin due to lack of oxygen in the blood. This condition is called cyanosis.