Spring 97 Newsletter INFACT Canada



Decreased thymus size in formula-fed infants compared with breastfed infants

Hasselbalch, H. et al. Acta Paediatr 85: 1092-1032, 1996

The thymus gland known to play an essential part in the development of the immune system was shown to be smaller in artificially fed infants. Noting in a previous study that the thymus of exclusively breastfed infants was larger than in other infants, the authors of this study compared the thymus size of 47 infants. Forty - five of the infants had initiated breastfeeding. The authors divided the test group into exclusively breastfed, partially breastfed and formula fed. The thymus size was determined at five days of age and again at 4 months. Initially there was no difference in the thymus size between the three feeding groups By four months of age, the thymus of the exclusively breastfed infants was larger than the partially breastfed infants and twice as large as the artificially fed infants. Although the authors did not determine the impact of breastfeeding on thymus size, they suggest that antiinfective or antiinflammatory factors in breastmilk better protects against illness and creates optimal growth conditions for the thymus. And breastmilk could have an active stimulatory effect on thymus growth. They suggest that since breastfeeding is normal, the thymus size of breastfed infants should be considered the normal size for infants and the size of artificially fed infants as suppressed. The effects of a reduced thymus are not known and further study is required to elucidate the factors in breastmilk that contribute to thymus growth.

A longitudinal analysis of infant morbidity and the extent of breastfeeding in the United States

Scariati, P. D. et al. Pediatrics 99: 1997

A longitudinal study from the USA, documenting the negative effects of not breastfeeding confirms the importance of breastfeeding for optimal infant health in developed countries. This study finds that breastfeeding protects against diarrhea and ear infections. The dose response results show that the more breastmilk the infant receives, the less the risk for developing diarrhea and ear infections. Mothers provided data by mail at ages 2, 3, 4, 5, 6, and 7 months. Infants were then classified into groups: exclusively breastfed, high, middle or low mixed breast and formula fed, or exclusively formula fed. Adjustments were made for infant age, gender , other liquid, solid intake, mother's education, occupation, smoking; family size and income; and daycare use. The authors concluded that breastfeeding protects US infants against the development of diarrhea and ear infections and that the protection is dose-response related. The more breastmilk an infant receives, the less likely that he or she will develop diarrhea or ear infection.

Breast cancer and Lactation History in Mexican Women

Romieu, I. et al. Am J of Epidemiol 143:543-552,1997

This case-controlled study examines the relationship between breast cancer and lactation history, as well as the dose-reponse relationship between lactation duration and breast cancer. Five hundred and six subjects were selected from newly identified cases in Mexico City between 1990 and 1992.
Duration of lactation, even short-term, was associated with reduced risk of breast cancer. Women who had breastfed for up to three months had an age-adjusted odds ratio of 0.48 compared to women who had never breastfed. Women who had breastfed for 37 to 60 months in total had an age-adjusted ratio of 0.27, and women who breastfed for more than 60 months had an odds ratio of 0.23. After adjustment for social, economic, family and reproductive history, the results remained the same; a significant decreasing trend in breast cancer associated with total duration of breastfeeding.
The authors are concerned that the decreasing lactation and the decline in fertility rates in the Mexican population "could lead to a major epidemic of breast cancer such as that observed in Western countries". They conclude that breastfeeding is "certainly a cost-effective intervention that should be promoted to protect the health of both mother and infant".

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