Preweaning diet programs postweaning plasma thyroxine concentrations in baboons.

We tested the hypothesis that breast- and formula-feeding of infant baboons affect postweaning plasma thyroid hormone concentrations and that differences in thyroid hormone concentrations are associated with long-term effects of infant diet on lipoprotein concentrations and cholesterol metabolism. Newborn baboons were breast-fed (n = 12) or fed formulas with a high polyunsaturated/saturated (P/S) fat ratio (n = 11) or with a low P/S ratio (n = 12) similar to baboon breast milk. Baboons were weaned at 14 weeks of age to a high cholesterol, saturated fat diet. Plasma thyroid hormone concentrations were measured in this group of baboons until about 223 weeks of age. Thyroid hormones were also measured at 400 weeks in a second group of adult baboons (n = 80) that as infants were either breast-fed or fed formulas with varying levels of cholesterol. Baboons breast-fed as infants averaged 11% higher (P < 0.03) thyroxine (T4) concentrations from 34 to 400 weeks of age compared with those fed formulas. From 70 to 400 weeks of age breast-fed baboons had 10% lower T3/T4 ratios (P < 0.03). Breast- versus formula-feeding did not affect postweaning T3 and fT3 concentrations. Postweaning thyroid hormone concentrations were not significantly affected by the P/S ratio or the cholesterol level of the infant formulas. The rank correlation of the means of the sire progeny groups for T4 and HDL-C concentrations was statistically significant (rn = -0.83; P < 0.05). Partial correlations of T4 concentrations with body weight, feed intake, or measures of cholesterol metabolism were not significant. T4 concentrations were significantly correlated with T3 concentrations (r = 0.42; P < 0.02), and T3 concentrations were correlated with bile acid synthesis rate (r = 0.47; P < 0.01), acyl-CoA cholesterol acyltransferase (r = 0.66; P < 0.001), and plasma HDL1-C levels (r = -0.49; P < 0.007). These effects suggest that altered thyroid hormone homeostasis may partially mediate the long-term differences in cholesterol metabolism caused by breast-versus formula-feeding.