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Friday, October 05, 2007

New Breastfeeding Study Gives Mixed Allergy Results

On September 12, I posted Exclusive Breastfeeding Doesn't Reduce Asthma or Skin Allergy Risk. In it I talked about the results from a large study of breastfeeding mothers that said:

Children who were exclusively breastfed for at least the first three months of life were no less likely to develop allergies or asthma than children whose nutrition included infant formulas.

This week a second breastfeeding study, of an even larger group of mothers, was published in the Journal of Allergy and Clinical Immunology. "Breast-feeding and atopic disease: A cohort study from childhood to middle age," by Melanie Claire Matheson et al. The abstract says:
The Tasmanian Asthma Study is a population-based prospective cohort study that has followed participants from the age of 7 to 44 years. Exclusive breast-feeding in the first 3 months of life was examined as a risk factor for atopic diseases by using multiple logistic regression and generalized estimating equation analyses.

Exclusively breast-fed babies with a maternal history of atopy were less likely to develop asthma before the age of 7 years, but more likely to develop asthma after the age of 7 years.

A press release quotes the study's lead author on the implications:
Dr Matheson said the research confirmed the current recommendations that high risk infants – those whose mothers had an allergy – should be exclusively breast-fed to protect against wheezing illness in small children.

However, recommendations that babies be exclusively breastfed to protect against asthma and allergy in the long term should be reconsidered.

Dr Matheson said further investigation was needed to determine why there was an increased risk of developing asthma after seven years of age.

"It could be that mothers are passing antibodies on to their babies or because of increased hygiene and reduced exposure to infections early in life," she said.

"The breastfed children in our study had fewer bacterial and viral infections, were more likely to be first born and in a higher social class – these all factors related to increased hygiene."

Dr Matheson said the study’s authors acknowledged there were many benefits of breastfeeding and were not suggesting that women with allergies should not breastfeed.

"However, if you are concerned about preventing allergy in your children, it may be more effective to implement other strategies such as not having carpet in your home," she said.

The study, a collaboration between the University of Melbourne, Monash University and the Menzies Research Institute in Tasmania, used data from more than 8500 people from the 36 year follow-up of the Tasmanian Longitudinal Health Study. It is the first in the world to follow subjects from childhood into middle age.

However, the study was almost immediately attacked by the Australian Breastfeeding Association in a release titled "Breastfeeding and allergy study flawed".
The question that needs to be asked is - how exclusive was the breastfeeding? The studied group of people were all born in 1961. Giving every newborn baby a nightly feed of artificial formula was routine in the 1960s. This was often without the mother's permission or knowledge. One exposure to non-human milk can sensitise a baby's immature gut and make them more prone to allergies.


According to the Australian Breastfeeding Association (ABA), there is nothing in this study to justify calling for any changes to the recommendations on breastfeeding. The causes of allergy and asthma are complex. Breastfeeding mothers should be reassured that one study is not a reason to ignore a large body of evidence that shows breastfeeding is the best way to feed an infant.

In the short term, I agree with the ABA's conclusion. Even the study's author continues to recommend that high-risk infants be exclusively breastfed.

It is possible, even likely, that the connection between breastfeeding and allergies after the age of 7 will turn out to be a statistical fluke rather than an accurate prediction. Both sides of the argument agree that more studies are needed. The Tasmanian study may be the first of its kind and vitally important for that reason alone, but as I always emphasize, one study, even a good one, is not sufficient to force people to change their practices unless the risks are immediate and severe. These are neither.

I'll keep an eye out for follow-up.

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