Please stop believing that coffee will make your boobs smaller

By Fusion Staff | March 14, 2016 | 4:48pm

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Can your morning cup of joe actually make your breasts smaller?

The notion that drinking coffee will “shrink” your breasts has become an urban legend of sorts, fueled by the internet and snaking its way into headlines, health roundups, and Facebook posts for years. But is there any truth to it? (I ask this question while bravely sipping a soy latte).

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First, the backstory. The myth originated back in 2008, when researchers from Lund University in Sweden published a small breast-cancer study about the ways caffeine interacts with a specific genotype.

Previous research had hinted that coffee might reduce breast cancer in carriers of the BRCA1 gene, but experts were unsure why. (BRCA 1 and 2 are the notorious “breast cancer” genes made famous by Angelina Jolie.) The Swedish researchers were curious to learn more, so they decided to look at another gene—one called CYP1A2*1F—since coffee is metabolized by the CYP1A2 enzyme, and the gene also plays a key role in estrogen metabolism. The researchers theorized that CYP1A2*1F might have a role in the whole coffee-reduces-breast-cancer arena.

Here’s where the trouble began: As a byproduct of the study, the researchers observed that a specific group of participants who drank three or more cups of coffee a day also had smaller breasts on average than women who did not.

For a slew of media, this note became headline news—with outlets from Glamour to the Daily Mail to Fox News suggesting that drinking lots of coffee may shrink your boobs, according to “science.”

And the story didn’t die in 2008. It continues to be mentioned in health stories related to coffee or breasts, and last month it even resurfaced as a “news” article that was shared nearly 200K times and re-reported by other sites, further spreading the myth.

But the truth is—the researchers didn’t find that coffee makes your boobs smaller. Not even close.

“The study does not report any causal link or change in [breast] size,” Helena Jernström, lead author on the study and an associate professor of experimental oncology at Lund University, told me over email.

Here’s where the confusion stems from: The study involved 269 women who were at high risk for breast cancer. The women were separated into two groups based on their CYP1A2*1F genotype (remember, that’s the gene being studied, and genes come in different forms). Women with an A/A allele were placed in one group and women with any C-allele were placed in a second group.

The study found—drumroll, please—that women with the C-allele version of the gene (131 women total) who also drank three cups or more of coffee a day and were not on hormonal birth control tended to have smaller breasts by volume.

Here’s what the paper says:

“Among women carrying at least one C-allele, moderate-to-high consumption [of coffee] was associated with lower standardised breast volumes compared with low consumption (896 vs 749 ml) whereas the standardised [breast] volumes were somewhat larger in women with moderate-to-high coffee consumption and the A/A genotype (797 vs 847 ml).”

Catch that? While the women with the C-allele who reported “moderate-to-high” coffee consumption tended to have relatively smaller breasts, the women with the A/A genotype who reported “moderate-to-high” coffee consumption actually had “somewhat larger” breasts. Go figure—the other group saw the opposite effect.

You can see this association mapped out here:

Not only that, the researchers only measured the women’s breasts once—so there was no active shrinking. Everything was just correlation.

Plus, the breast size results were based solely on women who were not using hormonal contraception, because, as the authors note:

“Among current hormonal contraceptive users, coffee consumption was not associated with breast volume and there was no significant interaction between coffee and CYP1A2*1F on breast volume.”

When you remove women on contraception, the overall sample size in the study goes from 269 to 145.

So what did the study tell us? While the researchers did observe an association between smaller breast size and coffee drinkers who carry a specific genotype, they also saw an association between bigger breast size and coffee drinkers who carried the other genotype (albeit less statistically significant).

Sure, it’s possible that someday a more conclusive link will be drawn between coffee and breast size in some women, but that day has not yet come. Am I concerned that my latte will give me smaller boobs? No. And you shouldn’t be, either.

Taryn Hillin is Fusion’s love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.