A recent study carried out by researchers from the University of Oxford and funded by Cancer Research UK determined obesity in women to be a significant risk factor for breast cancer. Assessing lifestyle factors such as alcohol consumption, smoking and weight, the strongest correlation was found between high BMI and levels of sex hormones (e.g. oestradiol). Higher levels of hormones have been cited as an important determinant for tumour growth. Obese and overweight women were found to have more of these hormones in their bloodstream.
The study did not however consider the hormone levels of women who had later developed cancer. Subsequently, the relationship between high hormone levels and lifestyle risk factors cannot be definitely affirmed. NHS Choices suggest that ‘Given this limitation, we cannot establish important facts, such as whether changes in a women’s weight cause corresponding changes in her hormone level, or whether higher levels of hormones have caused women to gain greater amounts of weight.
However, there is now increasing data is to show reduced risk of primary breast cancer is associated with weight loss (see article on Tim Byers). In addition, studies such as the on-going US ENERGY (weight reduction) trial should also help to identify whether weight loss is associated with reduction in breast cancer recurrence.