The effect of age on manganese uptake and retention from milk and infant formulas in rats.

Manganese nutrition of the neonate is poorly understood, due in part to a paucity of information on the amount and availability of manganese in infant foods. We have developed a suckling pup model to assess the uptake of manganese from fluid diets by using extrinsic labeling. Human milk, cow milk and infant formulas were fed by intubation to fasted rat pups and adults. Rats were killed after varying time periods, and tissues were removed and counted. A period of 6 h was found to be adequate to allow for stomach emptying while limiting tissue redistribution; 24 h was found to reflect pup manganese retention. From human milk, manganese retention was highest (greater than or equal to 80%) in pups less than or equal to 15 days of age; in older pups average retention decreased to 40%. Using d 14 pups to assess relative Mn uptake from diets, wholebody Mn uptake was highest from cow milk (approximately 89%); uptake from human and cow milk formula was similar (approximately 80%) whereas it was lower from soy formula (approximately 60%). These findings suggest that bioavailability of Mn from infant diets is very high during the suckling period. Since most formulas contain considerably more manganese than is found in human milk, Mn deficiency may be less of a concern than possible toxicity from formulas.