http://www.henryfordhealth.org/body....detail&ref=424
This study found, among other things that "By age 7, children given at least one antibiotic in the first six months and who were breast-fed for more than four months were three times more likely to develop allergies."
The allergies they looked at were "pets, ragweed, grass and dust mites."
The study involved 448 children. 49% of whom received antibiotics within the first 6 months. There are no other useful numbers in the press
release, and this is from an unpublished study so I can't look up the publication myself and see what kind of actual numbers they find.
I know that ~70% of babies are bf at birth, but I believe the rate falls to ~30% at 4 months.
That means I guess their sample size for breastfed babies was about 134.
Say that the rate of antibiotic use was the same in bf and bottle fed babies (though we can probably safely assume it's less). That means ~66 babies got antibiotics and 4 months of breastmilk.
What is the rate of these allergies in 7 year olds? I have no clue. Let's guess it's 20% of the total population of 7 year olds.
That would mean that if bf babies were 3 times as likely as non-bf babies to get these allergies, and 30% of babies are bf for 4 months, 15% are both breastfed and get antibiotics.
From this, I gather that:
90 kids in the study had allergies, of them 31 kids were in the group of both breastfed and receiving antibiotics. Seems significant considering we're guessing 66 had both breastmilk and antibiotics. That's a rate of about 50%. Yikes! Compare the rate of allergies in bf babies overall, though, and you get 23%, marginally greater than the overall population.
But wait! Fewer breastfed babies end up on antibiotics than non-breastfed babies. I'm not sure what that rate is, but given the decrease in rate of ear infections, let's say that the rate of antibiotic use with breastfed babies is half that of non breastfed babies.
Therefore, our sample of babies with both 4 months of brestfeeding and a dose of antibiotics in the first 6 months is now only 39 kids and
something like 20 of them with allergies. Hmmm. Now our sample size is too small to say much, but let's try: This means, again, that a huge fraction of those kids both bf and with antibiotics ended up with allergies. HOWEVER, the overall rate for allergies with 4 months of breastfeeding is now 15%, less than the overall population.
From all this, I would gather that breastfeeding protects against allergies, but the protection is likely because it is associated with a lower rate of antibiotics usage.
To all this I ask: Why are they comparing apples and oranges? How many of those kids were breastfed for *only* 4 months and received their antibiotics at some time between 4-6 months? (Breastfeeding rates drop fast as women return to work. Antibiotics use climbs quickly as babies enter daycare...)