Aloha asked (I'm paraphrasing here) where the studies supporting the occasional bottle were. It's a great question and works well to illustrate that the studies Mears cited don't contradict what I was saying and, in fact, have led me to one (funded by the Netherlands Asthma Foundation and the Dutch "Stichting Astmabestrijding" that supports my view.
Before I start with the studies, it's important to think about what abstracts are. They are like the back of a novel, an overview of what the main work contains. Almost a teaser, except without the spin. You should read an abstract to decide if the paper is relevant to whatever you are researching. They generally list the study's aims, the general methods and the main results.
For example, in Mears's (Mears' ?) first link , the last two abstracts in the "Allergic Disease" section illustrate best her point (please correct me if I'm wrong!). Both abstracts say that exclusive breastfeeding until 4 months helps prevent asthma. The first is a more general and earlier study. Two questions to ask: why four months and exclusive breastfeeding is better than what?
I'd like to say that I'm not going to argue the merits of the studies; I'm going to assume that the science is sound. That is not to say that the papers don't warrant critical thinking. They should be analysed, taken apart and held up to the light as all papers should. It's just that I'm not going to do it here. (They do all seem to be really good papers, though; I'm not trying to imply otherwise.)
So we read the first paper to find out those things. Four months was chosen because of their statistical findings and because it's natural biologically (ie that's about the earliest people start giving solids). Exclusive breastfeeding is better than breastfeeding and supplementing with formula. Because they didn't consider how much formula people used, a valid question is if that makes any difference and what that difference is. As I said before, I am not criticizing the study: it's impossible to do a study that covers every situation because it would be impossible to do a meaningful statistical analysis. For example, in this study, they took into account many exposure characteristics . One that they did not include in the analysis was the presence of parental asthma. They mention this in the paper, saying that inclusion could be misleading. Again, it's not a sign of bad science, it's an interesting question raised.
In fact, the last paper in the "Allergic Disease" section of Mears's first link is the study, by the same people, prompted by the question: should children of mothers who have asthma be breastfed? This question was raised by information gathered in the previous study. In short, the answer is yes. The abstract gives us that basic detail. It was a much more narrowly focussed study than the first. They looked at exclusive breastfeeding to age 4 months versus non-exclusive breastfeeding to age 4 months. This study, quite rightly, uses data gathered from the first to make assumptions about which factors are important in analysis. This study did not consider the amount of formula given once introduced and again, it is not a fault of the study, it is to keep the statistics meaningful which is necessary to draw any valid conclusions. (I can only reference the abstract -- the paper I had to buy. Curiousity got the best of me!)
So we still have our question about the occasional bottle. It is at this point that the conclusion Mears reached and the conclusion I reached differed. Mears is saying that it is better to be safe than sorry. My sons' doctors are saying that, based on their knowledge of allergies and asthma and their information on the current research (in progress as well as published), the occasional bottle is ok. But it is important to note the fact that the papers do not preclude the occasional bottle being harmful. They do, however, support the idea that a much lower frequency of formula use in mothers who are breastfeeding would be better in protecting a child from allergies and asthma.
Where to go from here? Well, any study about the occasional bottle's effect on asthma will probably cite one or both of the above studies. Most likely, the study will again use the data to make basic assumptions to set up their own parameters. What we need is a list of articles that have cited one of the two. Luckily, the first paper has a list of citations at the end . One of these papers is titled: "The effect of brief neonatal exposure to cows' milk on atopic symptoms up to age 5" . (This is the paper that Robinw was referring to, I believe.)
Here is the conclusion of the abstract:
Conclusion: Early, brief exposure to cows' milk in breast fed children is not associated with atopic disease or allergic symptoms up to age 5.
Now, if you read the paper (as opposed to just looking at the abstract), you will realize that it does not prove my point. It supports it somewhat, but does not prove it. Since I'm all for my viewpoint, I'll let you figure out why.
(I hope I have not made anyone giving formula to their child feel guilty. Not my intention -- I certainly don't believe you should feel guilty at all.)