A year ago I reported on some research which had found a link between elevated levels of a substance called C-reactive protein (CRP) and worse outcomes for women with breast cancer. CRP levels tend to be higher in individuals with insulin resistance (where insulin levels tend to be high but the tissues in the body are resistant to its effects). This association was probably the reason why one of the authors of this study recommended women with breast cancer take steps to reduce their insulin levels, though at the time I expressed doubt about her suggestion that the diet should be low in fat. If insulin control is the desired outcome, I suggest a diet low in carbohydrate.
Yesterday saw the on-line publication of a study which, again, suggests that insulin may be a provoking factor in breast cancer . The study compared insulin levels in more than 800 women with breast cancer, and a similar number without the disease. Women with the highest insulin levels were found to be at a 46 per cent increased risk of breast cancer. However, the associated between insulin levels and increased risk of breast cancer was only found to be significant in women who did not use hormone replacement therapy.
When the results were re-analysed for only women who were not taking hormone replacement therapy, those with the highest insulin levels were found to be almost 2.5 times at greater risk of breast cancer compared to those with the lowest levels.
We don’t know from studies of this nature whether high insulin levels actually cause breast cancer. However, any causal link between insulin and breast cancer would be strengthened by evidence that links the eating of foods that tend to cause high levels of insulin with increased breast cancer risk. As it happens, there is quite a body of evidence to this effect. See here, here and here for examples.
To my mind there are plenty of good reasons for keeping insulin levels low in the body. For women, there is mounting evidence that reducing risk of breast cancer is one of them.
Gunter MJ, et al. Insulin, Insulin-Like Growth Factor-I, and Risk of Breast Cancer in Postmenopausal Women. Journal of the National Cancer Institute 2008 [epub 30 Dec]