BREAST-FEEDING AND FORMULA FEEDING AFFECT DIFFERENTLY PLASMA THYROID-HORMONE CONCENTRATIONS IN INFANT BABOONS

We tested the hypothesis that plasma thyroid hormone levels in infant baboons are differentially affected by breast-feeding and nursery rear ing. Infant baboons were breast-fed (n = 17), or fed formulas with a h igh polyunsaturated to saturated fat ratio (P/S) (n = 13), or a low P/ S formula (n = 14). Plasma total triiodothyronine (T3) and free T3 (fT 3) concentrations increased from 4 to 14 weeks of age in infants fed e ither formula, but decreased in breast-fed infants. At 9 and 14 weeks of age, infants fed the formulas averaged 31% higher T3 and 53% higher fT3 concentrations compared with breast-fed infants. Although T3 conc entrations of the high P/S formula group compared with the low P/S for mula group were not different at any single age, from 4 to 14 weeks th e T3 averaged 19% higher in the high P/S formula group. Plasma total t hyroxine (T4) or free T4 (fT4) concentrations were not significantly d ifferent among the diet groups during the preweaning period. In summar y, formula-fed infants maintained higher plasma T3 and fT3 levels comp ared with breast-fed infants in the late pre-weaning period.