The immune system is very good at thwarting bacteria, viruses, and parasites that seek to do us harm, but sometimes it can go too far. The body protects itself from infection and injury with a cascade of biological events known collectively as inflammation. But when inflammation won’t go away, there’s trouble brewing. Over the past couple of decades, research has suggested that a chronic type of inflammation that affects the whole body is linked to diseases like type 2 diabetes and heart disease. (This is unlike the immune disorder in type 1, which targets the pancreas.) The details are still a little fuzzy, but here are some inflammation basics.

Eternal Flame
A cut to the finger, an opening to infection, causes an acute response: Infection-fighting cells of the immune system swiftly congregate around the wound. There, they release a bunch of therapeutic chemicals. Some of these increase blood flow to the area, while others cause fluid to flow in from surrounding tissues. The goal of this assault is to bring in a deluge of substances that can repair the wound and kill any invaders. The familiar and painful result, warm red puffiness in the cut’s vicinity, is a sign that the immune system is working full force to keep the body safe and initiate healing.

Normally, this process is localized to the area immediately surrounding a cut. And it’s usually temporary, since most injuries eventually heal. Sometimes, though, the agent that triggers an immune response doesn’t go away. That causes inflammation to switch into a chronic mode that’s abnormal and harmful. The symptoms of rheumatoid arthritis, for example, are caused by chronic inflammation of the joints as the body mistakenly attacks healthy tissue. The immune cells continue to linger and churn out their chemicals in a process that harms the body. Tissue damage is the hallmark of chronic inflammation.

Ignition and Afterburn
Many people with type 2 diabetes test positive for the chemicals associated with an active immune system, which is how researchers detect chronic inflammation. The most common inflammation test is for a molecule called CRP, or C-reactive protein. Doctors use a standard CRP blood test to check for diseases, like lupus, that are associated with a strong
activation of the immune system. Yet the test isn’t sensitive enough to detect the lower levels of CRP that often mark chronic inflammation. There is a high-sensitivity CRP test, though, that is sometimes used to assess heart disease risk, and scientists use that test to study the link between chronic inflammation and diseases like type 2 diabetes.

What causes chronic inflammation? One theory is that obesity, which has close ties to type 2 diabetes, is the driving force behind chronic inflammation. Fat cells that expand beyond healthy limits often die, triggering an immune system response. Studies have found an abundance of activated immune cells in the fat tissue of obese mice, supporting this theory. What’s more, signs of inflammation are also observed in people with heart disease, another ailment linked to obesity.

While nothing is certain, studies have shown that inflammation precedes type 2 diabetes, suggesting that inflammation could be a cause of the disease. Other research has shown that inflammation may spur insulin resistance by activating proteins that block insulin action. Insulin is the signal for fat and muscle cells to absorb glucose from the blood, while insulin resistance causes cells to ignore insulin. Once the body stops producing enough insulin to overcome the resistance, that leads to type 2 diabetes. Scientists haven’t proved that inflammation causes insulin resistance, though.

Researchers are more certain about the link between inflammation and heart disease. Chronic inflammation contributes to the development of atherosclerosis, the blood vessel damage that can lead to heart attacks and strokes. Atherosclerosis is the narrowing of blood vessels as plaque builds up along their interior. Much of that debris is made up of immune system cells called macrophages, which are the bad boys of chronic inflammation. The macrophages are presumably recruited to the blood vessels to repair damage caused by LDL (“bad”) cholesterol. But then they stick around and begin to do damage themselves.

Putting Out the Blaze
Losing weight cools the inflammation in people’s bodies, studies show. The result is the same whether the weight loss stems from diet, exercise, surgery, or other means. Medications can also lower inflammation, but most anti-inflammatory drugs are for short-term use only.

However, there are medications now under development for type 2 diabetes that work by stemming inflammation. For example, salsalate is an existing arthritis medication that is undergoing clinical trials to prove that it can also lower blood glucose in people with type 2 diabetes.  Another drug in development, which is still in the animal-testing phase, goes after macrophages as a way of treating type 2.

While chronic inflammation is indeed a fiery foe, there is an upside. If the connection between inflammation and type 2 diabetes is confirmed and more fully understood, dousing inflammation may offer a whole new route to tackle the disease.