DECREASED THYMUS SIZE IN FORMULA-FED INFANTS COMPARED WITH BREAST-FEDINFANTS

The objective of this research was to investigate if breastfeeding aff ects the size of the thymus. Ultrasound assessment of the thymic index (a volume estimate) at birth and age 4 months in 47 healthy infants b orn in the hospital were used. History of feeding mode, body size and illness were registered. At 4 months the geometric mean thymic index ( range) was 38.3 (16.2-83.2) in exclusively breastfed infants (n = 21), 27.3 (15.6-50.0) in partially breastfed infants (n = 13) and 18.3 (12 .2-32.6) in formula fed infants (n = 13; p = 0.0001,ANOVA). This findi ng was independent of weight, length, sex and previous or current illn ess. There was no significant difference in mean thymic index at birth between the three feeding groups and mean thymic index had increased in all three groups from birth to 4 months. For the formula-fed infant s it seems that the thymus remains large for a period and then decreas es in size after breastfeeding has been terminated. We conclude that t he thymus is considerably larger in breastfed than in formula-fed infa nts at the age of 4 months. The cause of this difference is unknown bu t human milk contains many immune modulating factors that might cause this effect.