Investigating the Link Between Type 2 Diabetes and Infection

It is commonly known that having type 2 diabetes can lead to the development of various health conditions, including heart disease, neuropathy, kidney disease, and eye disease. Not as well-known is the association between type 2 diabetes and infection, according to Kasia Lipska, MD, MHS, who recently published a paper on the risk of infection in older adults with type 2 diabetes.

“Infections are not typically considered traditional complications of diabetes, but they are an important reason why people with diabetes end up in the hospital,” said Lipska, an associate professor of medicine (endocrinology and metabolism) at Yale School of Medicine. “Infections are also a common cause of hospitalization among older adults, and older adults with type 2 diabetes are at increased risk.”

In a Q&A, Lipska discusses the impact of type 2 diabetes on the immune system and findings from her recent research.

Diabetes impacts the immune system in multiple ways. High blood sugar impairs the function of the body’s white cells, making it harder for the immune system to fight off infection. People with type 2 diabetes may also be susceptible to infection because of complications of the disease, such as neuropathy or peripheral vascular disease, in which they develop wounds on their feet. The combination of having high blood sugar and poor blood flow to the extremities makes healing difficult.

Guidelines for older adults recommend more relaxed blood sugar control than for younger adults because the risks associated with blood sugar becoming too low increase with age. Through our research, we wanted to learn whether the guidelines, which recommend keeping older people at higher blood sugar levels, increase the risk of infection. We wanted to find out if being on the higher end of the recommended range increases the risk of infection compared to being on the more tightly controlled end.

To do this, we broke up the recommended range of glycemic control from A1C levels of 6 to 7 percent, 7 to 8 percent, and 8 to 9 percent. We looked at the association between those three different ranges of glycemic control and being hospitalized for any or one of four kinds of infection—respiratory; genitourinary; skin, soft tissue, and bone; and sepsis—to see whether having A1C in these different ranges makes a difference.

We found that having A1C at the higher end of that recommended range is not associated with a significantly increased risk of hospitalization for any of those four infections. However, individuals with A1C between 8 and 9 percent had a 33 percent increased risk of having skin, soft tissue, and bone infections.

In my older patients, where it doesn’t make clinical sense to control their blood sugars very tightly, I will try to hit the 7 to 8 percent, the middle range, if I can do that safely without causing undue risk to the patient. But in patients who might have low blood sugar reactions at that range or who are starting a treatment or undergoing a transition—for example, to a nursing home—that relatively small risk of skin and soft tissue and bone infection may be outweighed by the benefits of keeping their blood sugar a little bit less tightly controlled.

COVID has made us all more aware that chronic disease is interconnected with acute infectious risk. Given that diabetes raises this risk, more studies need to be done to better understand that relationship and incorporate this risk into our calculations of not only the types of medications that we use for people with diabetes but also the glycemic control levels that are optimal for individuals with respect to their health.

Yale School of Medicine’s Section of Endocrinology and Metabolism works to improve the health of individuals with endocrine and metabolic diseases by advancing scientific knowledge; applying new information to patient care; and training the next generation of physicians and scientists to become leaders in the field. To learn more, visit Endocrinology and Metabolism.