Nutrition and immune system: the size of the thymus as an indicator of the newborn's nutrition status.

The thymus is a central lymphatic organ reaching its largest size after the delivery. Its size is significantly affected by endogenous and exogenous negative factors. In our research, we investigated the relationship between the size of the thymus determined by sonography and anthropometric parameters as well as indexes demonstrating the nutritional status. The examined group consisted of 212 full-term newborns, all of which passed an anthropometric examination during the first five days after delivery (birth weight and length, mid-arm and head circumference). The following nutritional status indexes were calculated from estimated anthropometric dimensions: Quételet's index, Rohrer's index, birth weight-to-length ratio and mid-arm-to-head circumference ratio. The size of the thymus was assessed by sonography and expressed as the multiple of transversal width of the cranial thymus part and sagittal area of the major thymus lobe (so-called 'Thymic Index'). The Thymic Index showed a positive correlation with the majority of indicators of the newborn's nutritional status, but all of these correlations are low (Spearman correlation coefficients 0.228-0.409). The correlation of the size of thymus with the birth weight or birth weight-to-length ratio was stronger than the correlation with the Quételet's index or mid-arm circumference. The size of the thymus reflects the newborn's nutritional status assumed by anthropometry and can represent one of the "barometers of nutrition". Normal nutrition in the prenatal period plays a relatively critical role in the development of the immune system.