Does Insulin Level Raise Risk for Breast Cancer?

A new study published in the International Journal of Cancer suggests that postmenopausal women with higher insulin levels may be at greater risk of developing breast cancer.

Insulin is a hormone that regulates blood sugar. Too much insulin in the blood is common in people who are obese and can be a sign of type 2 diabetes. It is also common among women with hormonal problems such as polycystic ovary syndrome. Too little insulin may indicate type 1 or type 2 diabetes. Normal values of insulin range from 5 to 20 micro units per milliliter (mcU/mL).

As Insulin Levels Increase, So Does Breast Cancer Risk

Researchers measured insulin levels in blood samples provided by 5,450 postmenopausal women who took part in a study called the Women's Health Initiative. The initiative was originally set up to determine the effect of hormone therapy, diet changes, and calcium plus vitamin D supplementation on postmenopausal women. More than 100,000 research volunteers ages 50 to 79 from across the U.S. took part. The study began in the mid 1990s.

For the present analysis, women were grouped by their insulin levels at the start of the study and based on the average of their insulin levels from blood drawn at years 1, 3, and 6 of the study.

Over eight years, 190 women developed breast cancer. Women with insulin levels in the highest third (13 mcU/mL or higher) were twice as likely to develop breast cancer as women in the bottom third (less than 8mcU/mL). This was true when researchers looked at insulin levels at the start of the study and when averaged throughout the study.

Results from prior studies that looked at insulin level and breast cancer have conflicted. But none of them examined insulin levels over time, like this study. Nonetheless, the researchers note that their findings require confirmation in larger studies.

Risk May Be Independent of Obesity

Although obese women tend to have higher insulin levels, the link between higher insulin levels and breast cancer was stronger for thin women than for obese women. This finding is important because it suggests that insulin may contribute to postmenopausal breast cancer risk, independent of obesity.

Reduce Your Risk for Breast Cancer

Keeping insulin levels in check may help lower risk for breast cancer. Losing weight and getting regular exercise can help you to do this. But other healthy habits can lower your risk, too. They include the following:

• If you use postmenopausal hormone therapy, use the lowest dose for the shortest time possible.
• Have no more than one alcoholic beverage per day.
• Maintain a healthy weight by balancing what you eat with how active you are.
• Exercise five or more days a week.

Always consult your physician for more information.