The association between insulin blood levels and risk of death in breast cancer patients

The present study evaluated the relationship between high insulin levels in the blood stream and the risk of cancer-related mortality. Its authors report that women with higher-than-normal insulin levels are at higher risk of death due to breast cancer.

Breast cancer has been shown to be more common in people who smoke, drink, have a high fat diet, or are obese.  Approximately 10% of all breast cancers patients also have a lifestyle which lacks physical activity.  Type 2 diabetes (T2DM) is also more common in people who are obese. The amount of people suffering T2DM has drastically increased in recent years from 30 million in 1985 to 285 million in 2010.  With obesity linking both breast cancer and type 2 diabetes, it is not surprising that there is an increased risk of breast cancer in people with T2DM.

The C-peptide is a byproduct created when the hormone insulin is produced. It is an indirect, and more accurate, measure of insulin blood levels. It is generally found in amounts equal to insulin. Normal C-peptide blood levels (after fasting for 12 hours) are 0.5 – 2ng/ml. C-peptide and insulin levels in type 2 diabetic patients are normal or higher than normal.

This paper looks at 604 women who were diagnosed with breast cancer that was confined to the breast or affected the lymph nodes around the breast (breast cancer stages I to III) between 1995 and 1998. These women all took part in a health, eating, activity and lifestyle study, and they were observed until they passed away or until the end of 2006. 546 of these women did not have T2DM, 58 of them did. C-peptide blood levels were measured 3 years after breast cancer was diagnosed in the participants.

Results showed that women who did not have T2DM but who did have C-peptide levels higher than 2.5ng/ml were almost three times more likely to die from breast cancer or any other cause. This was even higher in patients with diabetes type 2, and those who had higher stages of breast cancer, or estrogen receptor positive tumors.

This study stresses the importance of a balanced lifestyle. Lower C-peptide levels are associated with an improved prognosis. Lowering levels may be achieved by losing weight with an improved diet or in combination with increasing physical exercise. If diet and exercise do not control these levels then treatment with anti-diabetes drugs (e.g. Glucophage) or insulin may be an option.

The main limitation of this study is that blood C-peptide was measured only once instead of regularly. Such measurement may represent an exception rather than a trend. In addition, participants in this trial did not use aromatase inhibitors (AI). Thus it is uncertain if these findings apply for women taking AIs.

Well controlled diabetes may mean a better breast cancer prognosis. You should talk to your doctor about ways to lower C-peptide levels.