It has long been known that diabetes increases the risk of cancer, but a recent Kyushu University study shows that having only elevated blood sugar levels can increase the risk of dying of cancer.
Yoichiro Hirakawa, a medical doctor at the university's graduate school of medicine, led the study.
"It's widely known that diabetics have a higher risk of developing cancer," Hirakawa said. "But people with only elevated blood sugar levels should realize they are also at risk and take into account their lifestyles. It's important to eat and exercise properly."
About 2,400 cancer-free men and women aged 40 to 79 years old and living in Hisayamamachi, Fukuoka Prefecture, were enrolled in the study in 1988.
They were sorted into four groups based on measurements of blood sugar levels made both on empty stomachs and two hours after eating. Over 19 years from 1988 to 2007, 229 of the people in the study died of cancer.
The risk of cancer death for subjects with a fasting blood sugar level of more than 126 milligrams per deciliter was 2.1 times that of subjects with less than 100 milligrams per deciliter. Subjects with blood sugar levels of more than 126 milligrams per deciliter were strongly suspected to be diabetic.
The risk for subjects with a fasting level of 110 to 125 milligrams per deciliter was 1.9 times that of those with less than 100 milligrams per deciliter. Levels between 110 and 125 were higher than normal but not considered diabetic.
Concerning blood sugar levels two hours after eating, the risk for subjects with a level of more than 200 milligrams per deciliter was twice that of subjects with less than 120 milligrams per deciliter. Subjects with more than 200 deciliters were also strongly suspected to be diabetic.
Subjects with blood sugar levels of 140 to 199 milligrams per deciliter after eating, a level considered to be a little higher than normal, were 1.4 times more likely to die of cancer than subjects with less than 120 milligrams per deciliter.
By cancer types, the risk of dying of stomach cancer for those with a fasting blood sugar level of more than 100 milligrams per deciliter was 2.1 times higher than those with less than 100.
The risk for those with a level of more than 140 milligrams per deciliter after eating was twice as high as those with less than 140 in the case of lung cancer and 2.7 times higher in the case of liver cancer.
There was no clear difference in risks for other types of cancers.
Why are higher blood sugar levels associated with a higher incidence of cancer?
According to Hirotaka Watada, a professor at Juntendo University Hospital who specializes in diabetes and endocrine disease, cells work harder to metabolize excess glucose in the blood. For several reasons, including an increase in harmful "active oxygen," genes of cells are damaged in the process and later become cancerous.
Insulin, a hormone that reduces blood sugar levels, also causes cells to proliferate. Watada said, "There's no denying that insulin also helps increase the number of both normal and cancerous cells, and heightens the risk of cancer spreading."