About 25 per cent or one in four adults worldwide has a liver condition, often undiagnosed, that raises the risk for heart disease, according to a new American Heart Association scientific statement.

The condition, called nonalcoholic fatty liver disease (NAFLD), occurs when abnormally elevated amounts of fat are deposited in the liver, sometimes resulting in inflammation and scarring. "NAFLD is a common condition that is often hidden or missed in routine medical care. It is important to know about the condition and treat it early because it is a risk factor for chronic liver damage and cardiovascular disease," said P. Barton Duell, chair of the statement writing committee.

The statement is published in the Association's peer-reviewed journal Arteriosclerosis, Thrombosis, and Vascular Biology. There are two types of NAFLD: one when only fat is present in the liver (called non-alcoholic fatty liver), and the other when inflammation and scarring are also present (called non-alcoholic steatohepatitis, or NASH).

NAFLD often raises the risk of heart disease and is the leading cause of death in people with liver conditions. The diseases share many of the same risk factors, including metabolic syndrome (elevated blood sugar and blood triglycerides, increased abdominal fat and high blood pressure); Type 2 diabetes; impaired glucose tolerance (prediabetes); and obesity.

However, people with NAFLD are at a higher risk of heart disease than people who have the same heart disease risk factors without the liver condition. NAFLD can go undiagnosed for years, as the initial stages generally have no symptoms and people feel well, and routine blood tests may not show liver abnormalities.

Often, elevated liver enzymes in the blood, a possible sign of NAFLD, may be misattributed to a side effect of medication or to recent alcohol consumption. In addition, the absence of elevated liver enzyme levels does not rule out NAFLD or NASH.

According to the statement, a specialised ultrasound that measures liver elasticity, fat and stiffness (a result of scarring) in the liver can detect NAFLD. This type of liver scan is a non-invasive way to help diagnose and monitor treatment in NAFLD and NASH, yet it is underused. Liver biopsy is the definitive test for the diagnosis of more advanced stages of NAFLD, however, it is invasive and expensive.

However, NAFLD is often preventable by maintaining a healthy body weight, exercising regularly, eating a heart-healthy foods diet and managing conditions such as Type 2 diabetes and elevated triglycerides (a type of fat) in the blood, statement noted.