A study of 300 women done in the UK says that drinking 3 cups of coffee per day can cause a woman's breasts to shrink by an average of 17%.
drinking three or more cups a day was enough to cause a smaller breast size
However, I question the study's methods. It appears the study was done instantaneously, and did not measure the results of caffeine intake over time. Therefore, it seems at least plausible to me, that the correlation between breast size and coffee intake may be secondary, and there may not be a cause/effect relationship.
Perhaps women with smaller breasts have a biological or social reason for stronger coffee cravings, for instance.
It also seems possible that even if caffeine does affect breast size, it might happen during puberty, and the caffeine might cause breasts not to develop as fully. Yet the article claims that caffeine can actually cause breast shrinkage, not just under-development.
Is there additional research (or a better summary of this study) which confirms the reported claims that drinking coffee does cause breasts to shrink in size?