Why Diabetics Have an Increased Risk of Cancer

If you have diabetes or are at risk for the disease, there’s something you need to know. Diabetes and cancer— two of the most common diseases in the United States— share a stronger link than you might realize.

Let’s take a look at the evidence and what you can do about it...

In our research at Cancer Defeated we've seen for a long time that a diet high in sugar and other refined carbs is an underlying cause of both diseases.

We get news and tips from a large number of cancer patients and cancer survivors, and we find that when patients make the lifestyle changes necessary to get rid of cancer they often rid themselves of diabetes, too. (Sometimes they get rid of arthritis while they're at it, but that's a story for another day.)

Instead of relying on these anecdotes, my team investigated the science on the cancer-diabetes connection and found a LOT of research that shows your risk of cancer goes up if you have diabetes.

In the words of Frederick Brancati, M.D., professor of medicine and epidemiology at Johns Hopkins Bloomberg School of Public Health, "It's something that is hiding in plain sight. Diabetes is very common, cancer is very common, but no one had really thought to organize the literature and see it."¹

Connecting the dots between diabetes and cancer

Researchers analyzed research from multiple well-designed studies — called a meta-analysis. This approach can highlight problems that a single study might miss.

The evidence became so compelling that the American Diabetes Association and the American Cancer Society held their first consensus conference in 2009 — exploring the association between diabetes and cancer incidence, the risk factors common to both, and the causes of both.

They published a report in A Cancer Journal for Clinicians and revealed that diabetes:

• Increased risk of certain types of cancer. In Japan, researchers found that adults with diabetes were at increased risk of developing several kinds of cancer such as liver, kidney, and pancreatic cancers for men, and stomach and liver cancers for women, compared to those without diabetes.² 
• Increased risk of colon cancer. The University of Minnesota School of Public Health and University of Minnesota Cancer Center found women with diabetes were 1.5 times more likely to develop colorectal cancer than women without diabetes.
• Study author Dr. Andrew Flood, Assistant Professor in the Division of Epidemiology and Community Health, University of Minnesota School of Public Health, and colleagues, examined the records of 45,000 participants from a large study called the Breast Cancer Detection Demonstration Project. They chose participants with no history of colorectal cancer or diabetes at the beginning of the study, and followed the ones who later got colorectal cancer.
• Dr. Flood and colleagues found that women with diabetes had the greatest risk of developing colorectal cancer. "These results remained statistically significant even after controlling for all known and suspected confounding variables," reported Dr. Flood.³ 
• Increased risk of death from breast cancer. The Health, Eating, Activity and Lifestyle (HEAL) Study found that women with invasive breast cancer and elevated blood levels of C-peptide, a marker of insulin secretion, had a three times greater risk of death than women with lower C-peptide levels.
• Researchers followed 689 women without type-2 diabetes for nine years. They took regular fasting blood samples and other measurements like weight, height, age and lifestyle factors, and analyzed the link between C-peptide and risk of death, adjusting for other factors.
• They found the risk of death to be three times higher in the highest C-peptide group compared to the lowest C-peptide group.⁴ 
• Increased risk of death was highest in those with the highest blood sugar. In South Korea, a study of more than one million South Koreans suggests diabetes can raise the risk of developing — and dying from — several kinds of cancer. The highest risks were found in people with the highest blood sugar levels, says the study, which was reported in the Journal of the American Medical Association.
• Researchers analyzed data on 1.29 million South Koreans ages 30 to 95 through a health insurance group covering government employees, teachers and their families. The study followed participants for up to ten years, beginning in 1992.
• Those with diabetes were 30 percent more likely to develop and die from cancer than those who were diabetes-free. Pancreatic cancer showed the closest association with diabetes. This is no surprise, since the pancreas makes insulin. But diabetics were also at higher risk of liver, esophagus and colon cancer.⁵ 
• A 1.4 times greater risk of dying from cancer. A study at Johns Hopkins analyzed research from 23 studies looking at cancer patients who already had diabetes at the time they were diagnosed with cancer. They discovered that those with diabetes had a 1.4 times greater risk of dying from cancer than patients with no blood sugar problems. Mortality was statistically higher for breast, endometrial, and colorectal cancers.⁶ 

Overall, the risks from diabetes are greatest — twice as high, or more — for cancers of the liver, pancreas, and endometrium when compared to people who aren't diabetic. And the risks are approximately 1.2 to 1.5 times higher for colorectal, breast, and bladder cancer.

However, lung cancer doesn't appear to be linked to diabetes. And prostate cancer is the only cancer to be lower in diabetics. Of course, I don't recommend becoming diabetic to protect yourself against prostate cancer.

Why does diabetes cause cancer?  

Researchers say there are many possible reasons for a link between diabetes and cancer.

One big question is whether the association between diabetes and cancer risk is mostly due to shared risk factors, or whether diabetes itself — and the changes it makes in your body — directly cause cancer.

In other words, does bad diet lead to diabetes, which then leads to cancer, or does bad diet independently cause both at the same time? The mainstream doctors who conduct these studies might not put it that way, but I would. They like to speak of "risk factors" — they'll say "these two things are associated… they're found together." Strictly speaking, such correlations are not final proof that, "X causes cancer."

Researchers are looking into factors like obesity, poor diet, physical inactivity and aging.

Obesity is one of the highest risk factors for type-2 diabetes, and also a well-established risk factor for some cancers — especially cancers of the colon, endometrium (inner lining of the uterus), breast, kidney and esophagus.

However, in the South Korean study, diabetes was associated with higher mortality rates from cancer even though few study participants were overweight. In addition, other studies suggest that weight alone may not be the reason for an increase in death among diabetes patients.

People with diabetes are at increased risk of other health problems, like kidney and heart disease, as well as a weakened immune system —reducing their ability to endure chemotherapy or other aggressive treatments. Therefore, doctors may treat them less aggressively.

Doctors may also fail to spot cancer in diabetic patients, due to a focus on their other diabetes-related problems.

However, the most plausible possibility may be that high insulin levels create an environment conducive to cancer growth.

High insulin levels may breed cancer cells  

Dr. Edward Giovannucci, professor of nutrition and epidemiology at Harvard School of Public Health, notes that insulin and insulin-like growth factors (IGF) can promote some cancers.

Also, many people with type-2 diabetes have high levels of circulating insulin, quite possibly for years before they're diagnosed with diabetes. The majority of cancer cells express insulin and IGF-1 receptors. In addition to metabolic functions, the insulin receptor is also capable of stimulating cancer cell proliferation and metastasis. Insulin and IGF may also be able to stimulate normal cells involved in cancer progression.⁷

Lead author of the South Korean study, Sun Ha Jee, a public health researcher at Yonsei University in Seoul, said, "Insulin may influence cell growth. Cancer is characterized by runaway cell growth."

In the HEAL Study we mentioned earlier, researchers found a correlation between C-peptide levels and higher death rates. Dr. Melinda L. Irwin, assistant professor at Yale University School of Public Health, noted, "C-peptide and most likely insulin, in and of itself, is a marker for breast cancer prognosis."⁸

Dr. Irwin suggested, "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..."

Dr. Giovannucci and colleagues stress that it's important to also look at glucose as a potential cancer mediator, given the dependence of many cancers on glucose for energy.

Sugar fuels cancer growth  

As I've pointed out before in this newsletter, cancer lives on sugar. It's astounding that conventional oncologists often tell cancer patients, "Diet makes no difference at all to cancer treatment. Eat whatever you want."

Mainstream medicine should consider that chronic high blood sugar facilitates cancer growth.⁹

In fact, Larry Deeb, M.D., who was once president of the American Diabetes Association, told WebMD that these findings add to the evidence that those who lower their risk of type-2 diabetes, or control the disease if they already have it, may also reduce their cancer risk.

What does this mean for you? Do every thing you can to keep your blood sugar in check. For instance:

• Maintain a healthy body weight.
• Get active for at least 30 minutes every day. Take your dog or child for a walk — you'll all benefit.
• Eat a plant-based diet that's rich in a variety of vegetables, whole grains, legumes, nuts, lean meats and healthy oils such as olive or coconut.

Of course, it's also a good idea to limit alcohol consumption to one drink per day for women and two drinks per day for men. And don't smoke.

Alice Bender, nutrition communications manager for the American Institute for Cancer Research (AICR), says, "At least for cancer, we know that each factor (above) independently lowers the risk of certain cancers, but all three done together are even more powerful. And, I suspect that's the case for preventing type-2 diabetes also."¹⁰

Best regards,

Lee Euler,
Publisher

References:

1. Tamkins, Theresa, "Diabetes Increases Cancer Mortality Risk", CNNHealth.com.
2. Boyles, Salynn, "Diabetes May Raise Cancer Risk: Study Shows Liver, Kidney and Pancreatic Cancers More Frequent in Diabetes Patients", WebMD Health News.
3. "Diabetes and Cancer Risk in Women", Medical News Today.com.
4. "Diabetes and Cancer Risk in Women", Medical News Today.com.
5. "Study Links Diabetes to Cancer Risk", MSNBC.msn.com.
6. Tamkins, Theresa, "Diabetes Increases Cancer Mortality Risk", CNNHealth.com.
7. Giovannucci, Edward, MN, ScD, et al, "diabetes and Cancer: A Consensus Report", CA Cancer J Clin 2010.
8. "Diabetes and Cancer Risk in Women", Medical News Today.com.
9. Giovannucci, Edward, MD, ScD, et al, "Diabetes and Cancer: A Consensus Report", CA Cancer J Clin 2010.
10. "Scientists Tease Out Links Between Diabetes, Cancer", HealthDay, a service of the U.S. National Library of Medicine and the National Institutes of Health.