Published September, 2012 in PEDIATRICS Volume 130
Kwok, Leung, Lam and Schooling
This is a very limited study- but it appears that breastfed children reach puberty later than children who were not breastfed and instead were fed cow’s milk formula. The concern regarding this study is that there may be some socioeconomic issues that were factors as well.
You may ask why this is important. But “early puberty is associated with hormone related cancers and cardiovascular diseases.” So delaying puberty is certainly of interest to us now!
Cow’s milk formula is suggested as causing early puberty due to the specific nutrients in milk such as animal protein, animal fat, and calcium. It goes back to human milk for human babies. Is it no wonder that giving a different animal’s milk to a human would have proteins and fats and different calcium that we cannot absorb properly?
This study could not be replicated in different places around the world. The US showed more of a larger quantity of early onset of puberty based on quantity of milk consumed. The study showed different results based on quantity vs. frequency of milk consumption. They were concerned that there were many other factors that could be different in different populations. So they felt it was a bit inconclusive.
The other issue that arose with the study was the type of formula given. Some people were using soy based formula although it should not be substituted over cow’s milk without a medical reason for doing so. (This made me wonder how many families make decisions regarding formula use without getting advice from their pediatrician. And the concerns about soy are rampant regarding the estrogen issues in soy. )
This study was conducted beyond infancy- they looked at milk consumption at 6 months, 3 years and 5 years. The fallacy in the study was regarding infants on exclusive breastfeeding vs. some supplementation vs. formula feeding. In Hong Kong where the study was conducted, has a short breastfeeding duration thought to be due to moms returning to work quickly. Three months was the duration they were seeking for the study but many moms had quit exclusively breastfeeding within two months.
The study was also conducted looking at two factors- frequency of milk consumption and when consumption started. They did a lousy job of collecting the data since exclusive vs. part time breastfeeding was confusing to the stats.
They also seemed to have a hard time determining what constituted the onset of puberty. For girls it was a bit simpler- they looked at breasts development. But for boys it was conflicting if it was the genital stage or the testicular volume for boys. They decided to use the genital stage II to be the factor- and my guess is the testicular volume results were not looked at once they decided to use the genital status. But you can see this is not a precise situation.
They classified the children in a few ways: gender, the families- education, occupation and income and then infant maternal issues that included second hand smoke exposure, mother’s age at the birth and the place of the birth.
I think this study is too flawed to be a conclusive one. Relying on the mother’s recall on consumption and the various conflicting issues seem to corrupt the results.
I think we can hold that human consumption of human milk can cause less problems- but the onset of puberty based on frequency and quantity of consumption can just be considered a possible factor not a conclusive one.