Certain common viruses, including the genital herpes virus, might contribute to the risk of type 2 diabetes, a new study hints.
Type 2 diabetes is a highly prevalent disease, with older age and obesity being two of the major risk factors. Now the new study suggests that two herpes viruses -- herpes simplex 2 and cytomegalovirus -- might add to the risk.
Herpes simplex 2 (HSV-2) causes genital herpes, while cytomegalovirus (CMV) usually causes no symptoms, though it can be serious in newborns or people with severely weakened immune systems.
Once either virus invades the body, it's there to stay, lying dormant unless it is reactivated.
In the new study, European researchers found that adults who tested positive for either virus were more likely to develop prediabetes over the next seven years. Prediabetes refers to higher-than-normal blood sugar levels that often precede full-blown type 2 diabetes.
The findings -- recently published in the journal Diabetologia -- do not prove the herpes viruses directly raise prediabetes risk.
But the study did account for major diabetes risk factors like older age, obesity, sedentary lifestyle and family history of diabetes, said researcher Annette Peters, of Ludwig-Maximilians University and Helmholtz Munich in Germany.
And those factors did not explain the connection between the viral infections and prediabetes.
If the viruses, themselves, do affect blood sugar control, the researchers speculate it might be related to modulations in immune activity. That, in turn, might affect the endocrine system -- the complex hormonal system that, among many things, helps regulate blood sugar.
But that remains to be proven. And Peters said it's still possible there are other explanations for the herpes virus/prediabetes link -- including factors during childhood, when many herpes virus infections occur.
The notion that viruses could play a role in diabetes is not new, said Dr. George King, chief scientific officer at the Joslin Diabetes Center in Boston.
In fact, he noted, that possibility has been studied for years, though mostly focused on type 1 diabetes. Unlike the much more common type 2 diabetes, type 1 is an autoimmune disease, caused by an abnormal immune system attack on the body's insulin-producing cells.
The basic theory is that in some vulnerable people, certain viral infections might set off that immune response.
The possibility that certain viruses might also contribute to type 2 diabetes is "interesting," King said.
But the difficulty, he added, is that so many environmental factors affect type 2 diabetes risk. On top of that, King said, about 700 genes have been implicated in the disease -- with each having a small effect on the risk of developing it.
That means it's difficult to separate any effect of herpes viruses, per se. Plus, King said, any impact would likely be small.
The findings are based on 1,257 adults between 32 and 81 years of age who had normal blood sugar levels to start. Most also had antibodies to more than one type of herpes virus, an indicator of past infection.
CMV was very common, with 46% of participants positive for antibodies, while 11% were positive for HSV2. Antibodies to some other herpes viruses were detected in the vast majority of participants, including Epstein-Barr virus, which can cause mononucleosis, and HSV1, which most often causes cold sores.
Over seven years, 364 people developed prediabetes. Traditional risk factors like older age and obesity were the main drivers, but HSV-2 and CMV also emerged as factors.
People with HSV-2 had a 59% higher risk of prediabetes, and those with CMV had a 33% higher risk compared to people without those infections.
King pointed to one key factor the study could not consider: people's diets.
Even in childhood, he noted, diet and other environmental exposures could be important, since they shape the gut microbiome -- the vast collection of bacteria that naturally dwell in the gut.
Those bacteria play a role in immune function, and research has linked the makeup of the gut microbiome to various chronic ills, including type 2 diabetes.
Peters said more research is needed to understand what is going on. She pointed out that the COVID-19 epidemic has shed light on the connection between viral infections and chronic ills, and research into the mechanisms is beginning.
It remains to be seen, the researchers said, whether preventing herpes virus infections -- including through new vaccines -- could have any effect on diabetes risk.
The U.S. National Institute of Diabetes and Digestive and Kidney Diseases has more on type 2 diabetes.
SOURCES: Annette Peters, PhD, professor, Ludwig-Maximilians University, and director, Institute of Epidemiology, Helmholtz Munich, Munich, Germany; George King, MD, chief scientific officer, Joslin Diabetes Center, Boston; Diabetologia, May 11, 2022, online