Does drinking coffee reduce breast size?

Question

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?

Answer 1

Fortunately, the study in question, Coffee intake and CYP1A2*1F genotype predict breast volume in young women: implications for breast cancer, is available online.

The basic answer is that the study provides no indication of an influence of coffee consumption on breast size. The best summary I found in the paper reads:

Our main finding was a significant interaction between coffee consumption, CYP1A2*1F genotype and breast volume among young healthy women who did not use hormonal contraceptives. This interaction was mainly driven by the fact that a moderate-to-high coffee intake was associated with lower breast volume in women with the C-allele. No association between coffee and breast volumes was observed in women with the CYP1A2*1F A/A genotype or in women who currently used hormonal contraception.

This means there is likely to be some connection between three factors: breast size, coffee consumption, and genotype. The authors do not make any claims about casualty in any direction, which makes sense as what they studies was the effect of coffee consumption on the cancer risk, which they expected to counteract the risks stemming from breast size. Whether the researcher really made the claims cited in the Telegraph, and if so, what these claims are based on, is an interesting but probably unanswerable question. However, it seems that the authors are at least partially responsible for this interpretation: the title of the paper explicitly talks about coffe intake predicting breast volume, something that the body of the article does not include. In fact, there is a previous study by the same leading author entitled Insulin-like growth factor-1 (IGF1) genotype predicts breast volume after pregnancy and hormonal contraception and is associated with circulating IGF-1 levels; once again, the body of the article uses weaker terms like "interaction" or "association", not "prediction". And causation is certainly not on the agenda anywhere.