A ten-year study of 535 women being given standard treatment for breast cancer found that those with the highest insulin levels were eight times more likely to die than those with the lowest levels. 30% of those with the highest levels had died within seven years compared to 5% of those with normal levels. Furthermore, the women with the highest levels were four times more likely to suffer a recurrence or a spreading of the disease to other parts of the body.

The researchers advise women with high insulin levels to reduce them through diet and exercise.

For a possible mechanism see Do sugary drinks increase risk of breast cancer?