Drinking too much coffee 'could shrink women's breasts'

According to the Daily Mail, women's breasts shrink when they consume three cups of coffee a day. It stated that after asking nearly 300 women about their coffee consumption, researchers assessed each woman's bust size. "Three cups was enough to make breasts shrink," according to the study, and the effect was stronger with each cup. Because around half of all women carry a gene that correlates coffee consumption with breast size, the newspaper said that there is "a clear link between drinking coffee and smaller breasts."

Previous study has discovered that the risk of breast cancer may be influenced by a certain oestrogen balance in the body, which appears to be connected with breast volume. This is controlled by a gene that codes (instructs) an enzyme involved in the metabolism of both estrogen and caffeine. The current study investigated whether coffee consumption is connected with breast volume, and how this is influenced by a woman's CYP1A2*1F genotype. Although the study found a correlation between these characteristics in women who did not use oral contraception, the media oversimplified the findings, and the study has little current implications. According to the publication, there is "a clear link between drinking coffee and smaller breasts" because almost half of all women carry a gene that relates breast size to coffee use.

What was the source of the story?

This study was conducted in Sweden by Dr. Helena Jernström and associates from Lund University and Malmo University. Several Swedish foundations as well as The Swedish Research Council provided funding for the study. The research was released in the British Journal of Cancer, a peer-reviewed medical journal.

Which type of scientific investigation was this?

In order to determine if coffee consumption was related to breast volume and how the A/A genotype of the CYP1A2*1F gene affected this, the investigators conducted a cross-sectional study. This gene produces the CYP1A2 enzyme, which is involved in the metabolism of estrogen and coffee. It has previously been demonstrated that high-caffeine A/A genotype women had a larger ratio of certain oestrogens, which may provide some protection against breast cancer.

The researchers recruited 269 Swedish volunteers (average age 29) who filled out a questionnaire about reproductive issues, contraception use, smoking, coffee consumption (big 300ml cups or tiny 150ml cups), and other topics (not covered in this article). Body measurements were recorded at specific intervals during the menstrual cycle. The women's breast volume was measured by asking them to kneel with their breasts hanging down. The approximate volume was then calculated using a simple formula (base x height divided by three). The CYP1A21F gene, as well as oestrogen and other hormonal factor levels, were analyzed in a laboratory. In their statistical studies, the researchers looked for any links between the CYP1A21F genotype (whether A/A or not) and consuming three or more cups per day.

What were the outcomes of the study?

The CYP1A21F A/A genotype was present in 51% of the women. There was no difference in coffee intake or any other personal, social, or lifestyle trait between women with the CYP1A21F A/A genotype and those without. Coffee drinking was significantly linked to smoking. Total breast volume was substantially linked with weight, but not with age, hormonal contraceptive use, childlessness, smoking, or the CYP1A2*1F genotype.

In subsequent analyses, the researchers focused primarily on women who did not use hormonal contraception (such as the pill). Among the 145 non-users, the CYP1A2*1F genotype significantly altered the relationship between drinking at least three cups of coffee per day and breast volume. Women who did not have the A/A genotype and drank three cups or more per day had smaller breast volumes than those who drank less coffee. Women with the A/A genotype who drank three cups or more per day had slightly higher breast capacity than those who drank less coffee.

What conclusions did the researchers make from their findings?

The authors conclude with the major conclusion of "a significant interaction between coffee consumption, CYP1A21F genotype, and breast volume among young healthy women who did not use hormonal contraception." According to the researchers, this interaction was primarily driven by the fact that drinking three cups of coffee or more per day was associated with reduced breast volume in women who did not have the CYP1A21F A/A genotype.

What is the NHS Knowledge Service's assessment of this study?

This is a sophisticated study that builds on previous research into the relationship between CYP1A2*1F genotypes, breast volume, and breast cancer. The media has oversimplified the research, and the findings have limited present relevance. The cross-sectional study design simply shows relationships; it does not prove that coffee drinking 'caused' the breast volume measured at the time of the study or caused the breasts to'shrink'. Furthermore, there may be concerns with both the accuracy of the breast measurement and coffee consumption (which are not included in this research). The observed relationship is based on an examination of only 145 women, and additional research will be required to confirm the findings.

Many women will have consumed coffee for most of their lives. These women need not be concerned about their breast size if they continue to consume moderately.