Surprising Link Between Blood Sugar and Brain Cancer Found

Diabetes raises risk for many cancers, but not most common malignant brain tumor

Newswise, May 3, 2017—New research further illuminates the surprising relationship between blood sugar and brain tumors and could begin to shed light on how certain cancers develop.

While many cancers are more common among those with diabetes, cancerous brain tumors called gliomas are less common among those with elevated blood sugar and diabetes, a study from The Ohio State University has found. 

The discovery builds on previous Ohio State research showing that high blood sugar appears to reduce a person’s risk of a noncancerous brain tumor called meningioma.

Both studies were led by Judith Schwartzbaum, an associate professor of epidemiology and a researcher in Ohio State’s Comprehensive Cancer Center. The new glioma study appears in the journal Scientific Reports.

“Diabetes and elevated blood sugar increase the risk of cancer at several sites including the colon, breast and bladder. But in this case, these rare malignant brain tumors are more common among people who have normal levels of blood glucose than those with high blood sugar or diabetes,” Schwartzbaum said.

“Our research raises questions that, when answered, will lead to a better understanding of the mechanisms involved in glioma development,” she said.

Glioma is one of the most common types of cancerous tumors originating in the brain. It begins in the cells that surround nerve cells and help them function.

The disease is typically diagnosed in middle age. At present, there is no treatment that ensures long-term survival, but several potential options are being studied.

The Scientific Reports paper included data from two large long-term studies. One, called AMORIS, included 528,580 Swedes. The second, Me-Can, consisted of 269,365 Austrians and Swedes. In all, 812 participants developed gliomas.

Schwartzbaum and her collaborators evaluated blood sugar and diabetes data and its relationship to subsequent development of brain cancer and found that those with elevated blood sugar and diabetes had a lower risk of developing glioma. 

“This really prompts the question, ‘Why is the association between blood glucose levels and brain cancer the opposite of that for several other cancerous tumors?” she said.

The researchers found that this relationship was strongest within a year of cancer diagnosis.

“This may suggest that the tumor itself affects blood glucose levels or that elevated blood sugar or diabetes may paradoxically be associated with a protective factor that reduces brain tumor risk,” Schwartzbaum said. 

“For example, insulin-like growth factor is associated with glioma recurrence and is found in lower levels in people with diabetes than those who don’t have the disease.”

The brain accounts for only about 2 percent of body weight, but consumes about 20 percent of the body’s available glucose, Schwartzbaum said.

The body of research on restrictive diets and their effect on brain cancer development has shown mixed results and more work is needed to determine if there’s something about the sugar/tumor relationship that can be modified in a way that’s beneficial to brain cancer patients, she said.

The research was supported by the National Cancer Institute.

Schwartzbaum’s collaborators included co-lead author Michael Edlinger of the Medical University of Innsbruck in Austria and Grzegorz Rempala of Ohio State’s College of Public Health.

Study Bodes Well For Low-Carb Eaters

Newswise,  November 15, 2016—Three low-carb meals within 24 hours lowers post-meal insulin resistance by more than 30 percent, but high-carb meals sustain insulin resistance, a condition that leads to high blood pressure, prediabetes and diabetes, according to a University of Michigan study.

The study also found that two hours of moderate-intensity exercise, which is supposed to lower insulin resistance and blood sugar levels, has no impact on these results.

To the contrary, blood sugar levels increase after the exercise, said Katarina Borer, professor in the School of Kinesiology and principal investigator in a study done with doctoral student Po-Ju Lin, now at the University of Rochester Medical Center.

Insulin is a hormone critical in metabolism. Insulin sensitivity refers to insulin's ability to efficiently respond to and regulate glucose in the blood, so that our cells can use it for energy and other functions.

If we're insulin resistant, insulin is less effective in removing glucose from the bloodstream and the pancreas must produce more insulin to help. This can eventually lead to diabetes.

The study sample was small, Borer said, but the results are significant, in part, because they reinforce results in two preceding studies and one 2015 review on high-carbohydrate diets and their negative effects on insulin.

In the U-M study, 32 post-menopausal metabolically healthy women were divided into four groups and given meals of either 30 or 60 percent carbohydrates with or without moderate-intensity exercise before meals. The low-carb group showed a reduction in insulin resistance after the third meal in the evening, but the high-carb group sustained high post-meal insulin, Borer said.

The high-carb group's diet fell in line with the 45-to-60 percent daily carbohydrate intake the departments of Agriculture and Health and Human Services recommend, Borer said.

"We showed an acute, one-day reduction in insulin resistance after the third low-carbohydrate meal eaten in the evening, so one could argue that this is transient and insignificant," Borer said.

"But at least two other studies where high-carbohydrate meals were fed to volunteers for 5 and for 14 days show that the outcome was worrisome.

“These subjects developed increased fasting insulin secretion and insulin resistance, increased glucose release by the liver which produced high blood sugar, and dramatically lowered fat oxidation that contributes to obesity. These then were more persistent effects that could be a path to prediabetes and diabetes.

"What is remarkable about our findings is that they show that a simple dietary modification of reducing the carbohydrate content of the meals can, within a day, protect against development of insulin resistance and block the path toward development of prediabetes while sustained intake of high carbohydrate diets as shown in the two mentioned studies lead to increased fasting insulin secretion and resistance.

“ And even more surprising and amazing is that exercise before the meals made the subjects more carbohydrate intolerant—that is, it increased evening blood sugar levels."

Because exercise did not lower insulin resistance, it suggests that the insulin reaction the subjects experienced after the evening meal was driven by an intestinal response to the carbohydrate, and not by exercise. But this doesn't mean exercise doesn't influence insulin, she said.

Going forward, Borer's lab will examine the timing of meals and whether insulin-lowering effect can be produced in the morning and whether blood sugar will decline when women exercise after low-carbohydrate meals.

The study, "Third exposure to a reduced carbohydrate meal lowers evening postprandial insulin and GIP responses and HOMA-IR estimate of insulin resistance," appears in the Oct. 31 edition of PLOS ONE.