As a scientist working in the fields of lactation, immunology and nutrition, I would caution everyone not to make too much of the recent study finding a difference in thymus size between breast-fed and non breast-fed infants. While the possiblities are interesting, we do not know what effect this difference would have on "real-life" outcomes like cancer risk, infectious disease resistance and autoimmune disease susceptability. To make an analogy, if we found that non breast-fed infants weighed more than breast-fed infants of the same age, we would not know if the difference was due to fatness, increased muscle mass or extra retained water - any one of which would change our perception of the study. -------- J. Paul Zimmer, Ph.D. Developmental and Clinical Immunology University of Alabama at Birmingham