Breast Cancer, Blood Sugar, Body Fat

"Big C risk is worse if you're fat" reads the headline in The Sun today. The news story it refers to goes on to say that fat women are "less likely to get low-risk breast cancer - but more prone to life-threatening versions". The researchers have "discovered a link between the fiercest types [of breast cancer] and high blood sugar", the newspaper adds.

The newspaper report is based on a Swedish study investigating metabolic factors and breast cancer risk. There were few results of statistical significance this study so it is impossible to reach firm conclusions. Although this study adds evidence to previous research which suggests a complex link between metabolism and breast cancer, more studies are needed to identify what this risk is. This study is not conclusive and The Sun and other news sources have overstated its significance.

Where did the story come from? Dr Anne Cust, Tanja Stocks and colleagues from the University of Melbourne, the University of Sydney, the International Agency for Research on Cancer (France), Umea University in Sweden and the German Cancer Research Centre carried out this research. The study was funded by the World Cancer Research Fund, the Swedish Cancer Society and the council of Vasterbotten county in Sweden. It was published in Breast Cancer Research and Treatment, a peer-reviewed medical journal.

What kind of scientific study was this? The study was a nested case-control study designed to explore the relationship between body mass index (BMI), the hormones involved in metabolism (leptin and adiponectin), some of those involved in controlling blood-sugar levels (C-peptide and glycated haemoglobin) and breast cancer risk among women in northern Sweden.

The researchers had access to data from several different groups of women who were involved in the Northern Sweden Health and Disease Cohort (NSHDC). One part of the NSHDC ran from 1985 to 1996 and another part has taken place since 1995. In September 2005, they linked all women for whom they had blood samples to the regional cancer register (which records 99% of breast cancer diagnoses). Of these women, 561 had a diagnosis of breast cancer. From the same population (i.e. women who came from the original groups and had blood sample records available), they selected one control for each case. The case-control pairs were matched on age at baseline and the date when their blood samples were taken.

The researchers looked at the blood samples from the women who had breast cancer and compared them with those who did not. They were particularly interested in whether the levels of particular hormones that regulate metabolism (leptin and adiponectin) were different between the groups. They also compared the levels of chemicals involved in regulating blood sugar: C-peptide and glycated haemoglobin.