Scientists have been studying the role of the liver in diabetes — especially type 2 diabetes — for a long time. Among its many other functions, the liver acts as a “storage tank” for glucose in the body, absorbing glucose from the blood or releasing it as needed. This function doesn’t always work as it should in people with type 2 diabetes, and one of the ways the first-line drug for the condition, metformin, works is to stop the liver from releasing excess glucose into the bloodstream.
Type 2 diabetes and NAFLD
But liver dysfunction in type 2 diabetes can go beyond the organ’s role in regulating blood glucose levels. People with type 2 diabetes are at increased risk for nonalcoholic fatty liver disease (NAFLD), a condition in which abnormally large amounts of fat build up in the organ. While this condition doesn’t tend to cause symptoms by itself, it increases the risk of inflammation and structural changes (fibrosis and cirrhosis) in the liver that can reduce liver function over time, and possibly lead to liver cancer.
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Because of the increased risk of liver disease in people with type 2 diabetes, doctors often pay special attention to certain blood markers of liver function in this group of people — as seen in routine blood tests. But according to a recent study, some of the most commonly used markers of liver function aren’t actually very good at predicting liver damage in people with type 2 diabetes.
New NAFLD research
Presented in June 2020 at the American Diabetes Association Scientific Sessions, the study by researchers at the University of Florida recruited 564 adults with type 2 diabetes. As noted in a Healio article on the study, none of these participants had a previous diagnosis of nonalcoholic fatty liver disease. All of them underwent laboratory testing to screen for liver fibrosis, which included common blood tests as well as an imaging test known as vibration-controlled transient elastography. Based on these screening tests, participants suspected of having substantial fibrosis underwent a liver biopsy to confirm the diagnosis.
Based on the imaging test, about 22% of participants were found to have some stage of suspected fibrosis in their liver. But two of the blood tests often used to screen for liver disease — aspartate aminotransferase (AST) and alanine aminotransferase (ALT) — weren’t very good at indicating this suspected damage. Among the participants with signs of fibrosis in their imaging tests, 71% had a normal AST result, and 62% had a normal ALT result. Overall, a higher body-mass index (BMI, a measure of body weight that takes height into account) predicted a higher risk of liver fibrosis.
Screening for NAFLD in type 2 diabetes
Based on these findings, the researchers recommended adding imaging tests to screening for nonalcoholic fatty liver disease in people with type 2 diabetes — since other tests may not pick up signs of the condition. They also emphasized the importance of screening in the first place, since even though none of the study participants had a previous diagnosis of liver disease, almost one in four showed signs of the condition. It’s unclear how many of these participants received screening that missed signs of liver disease, or how many didn’t receive any recent screening for liver problems.
As noted in the Healio article, liver fibrosis is the most important predictor of progression to cirrhosis, which involves more severe liver damage, and cancer (hepatocellular carcinoma). This study represents the first time that the imaging used to screen for fibrosis (vibration-controlled transient elastography, marketed as FibroScan) has been tested systematically in a group of people with type 2 diabetes in the United States. The average age of participants was 60, with 56% of them women, and they had an average HbA1c level (a long-term measure of blood glucose control) of 7.5%, and an average BMI of 33.3. The study was conducted at a variety of internal medicine, family medicine, and endocrinology clinics, mostly at participants’ normal point of care for diabetes-related checkups and similar appointments.