Plasma osmolality and feeding practices of healthy infants in first three months of life.

Plasma osmolality was measured in 60 healthy infants aged 1 to 3 months. The mean plasma osmolality in the 14 breast-fed infants (group A) was 284.3 mOsm/1. Nine infants fed artificial milk formulae alone (group B) had a mean value of 293.8 mOsm/1.; 37 infants already receiving solid foods in addition to artificial milk formulae (group C) had a mean value of 297.1 mOsm/1. The number of individual observations in the hyperosmolar range (more than 300 mOsm/1.) in groups A, B, and C were 0, 1, and 15, accounting respectively for 0%, 11.1%, and 40.5% of the total number of observations in each group.These results suggest that the early introduction to solid foods and the widespread use of artificial milk formulae at the expense of breast-feeding during the first three months of life result in an excessive dietary solute intake. This considerably stretches the ability of the immature kidney to maintain normal plasma tonicity. Minimal loss of water could precipitate a dangerous situation for babies with hyperosmolar plasma.