Obesity, metabolism, diabetes and increased risk of cancer are linked in a number of ways, according to studies presented at the Sixth Annual International Conference on Frontiers in Cancer Prevention Research of the American Association for Cancer Research that was held in Philadelphia, Pennsylvania from 5th to 8th December.
The studies showed that an increased risk of getting a number of cancers affecting both men and women, such as breast, prostate and colorectal cancer, is linked to weight gain and diabetes.
One such prospective study, by researchers from the University of Minnesota, found women with diabetes were 1.5 times more likely to develop colorectal cancer than women who did not have the metabolic disorder.
This was presented as “Abstract no. B93: Diabetes and hyper-insulinemia as predictors of risk in a prospective cohort of women”.
Study author, Dr Andrew Flood, assistant professor in the Division of Epidemiology and Community Health at the University of Minnesota School of Public Health and the University of Minnesota Cancer Center, said that:
“In general, the idea is that if elevated insulin levels create a biochemical environment conducive to cancer growth, it provides one mechanism by which diet and lifestyle can really influence cancer risk,” he added.
Flood and colleagues examined records of 45,000 participants from a large study called the Breast Cancer Detection Demonstration Project which was launched in the 1970s and covered 29 centres throughout the US.
They selected the participants who had no history of colorectal cancer or self-reported diabetes for eight years (between 1987-1989 and 1995-1998) and followed the ones who subsequently developed colorectal cancer.
The researchers found that women with diabetes had the greatest risk of developing colorectal cancer. As Flood explained:
“These results remained statistically significant even after controlling for all known and suspected confounding variables.”
Speculating on their findings, the researchers suggested it could be the higher level of insulin that is typically found in people with type II diabetes that contributes to the elevated colorectal cancer risk.
“In the early stages of the disease process, people become insulin resistant, meaning they must produce more and more insulin to regulate their blood sugar,” said Flood.
According to Flood, insulin levels stay chronically high for some time before the pancreas can no longer supply the insulin demanded by the body.
“If the elevated insulin is the problem, then pre-diabetics, who are also hyper-insulinemic, should also be at increased risk,” he said.
Flood and colleagues tested their hypothesis by analysing the data again, this time looking at women who were likely to be showing early signs of diabetes at the start of the follow up period. It is likely these women were hyper-insulinemic at that stage, said the researchers. But, surprisingly, the higher risk dropped slightly compared to the known diabetics, although it was still significant, said Flood.
The researchers concluded that either the pre-diabetic women had not been experiencing higher insulin levels long enough, or at sufficient intensity, to increase their risk of colorectal cancer (compared to the women who were diabetic), or something other than, or as well as, the hyper-insulinemia, explained the significant increased risk of colorectal cancer in the women with diabetes.
Another study was titled “Abstract no. B99: Fasting C-peptide levels and breast cancer death in women with breast cancer: The Health, Eating, Activity and Lifestyle (HEAL) Study”.
This showed that women with invasive breast cancer and elevated blood levels of a marker of insulin secretion known as C-peptide, had three times higher risk of death than women with lower C-peptide levels. The effect was strongest amongst the women in their 40s, said the researchers.
The women were enrolled in a long-term observational study of breast cancer patients called the Health, Eating, Activity and Lifestyle (HEAL) Study.
“The simple message is that breast cancer patients should take proven steps to lower their blood insulin levels, including exercise and eating a diet rich in fruits and vegetables and low in fat,” said Dr Melinda L Irwin, assistant professor at Yale University School of Public Health.
The researchers followed 689 women with breast cancer who did not have type 2 diabetes for up to 9 years, until 2004. The main outcome measure was death. They took regular fasting blood samples and a range of other measures such as weight, height, demographic and lifestyle factors.
The researchers then analysed the links between C-peptide levels and risk of death, adjusting for confounders such as body mass index (BMI), age, race, disease stage and therapy used in treatment.
They sorted the results into three groups according to C-peptide level. Women with the highest level of C-peptide (the top third) had double the risk of death compared to women with the lowest level of C-peptide (the bottom third).
For women with invasive breast cancer, the risk of death was three times higher in the top C-peptide group compared to the lowest C-peptide group.
“Our findings clearly show that C-peptide and most likely insulin, in and of itself, is a marker for breast cancer prognosis,” said Irwin.
Irwin also said the link was common in women in their 40s who had early stage breast cancer, and not so strong in women in their 50s and 60s.
“The higher death rate among younger women suggests that these women may have had more aggressive tumors, possibly related to tumor genetics or family history,” she added.
Other studies presented at the conference included:
“Abstract no. B89: Association of C-peptide concentration with prostate cancer incidence in a prospective cohort.”
“Abstract no. B95: Post-diagnosis weight change, body mass index, and breast cancer survival.”
Written by: Catharine Paddock