Non-alcoholic fatty liver disease (NAFLD), a common condition that is often hidden or missed in routine medical care, is a significant risk factor for cardiovascular disease, according to a an American Heart Association scientific statement.
It is estimated that about one in four adults worldwide has a liver condition that is a risk factor for heart disease, according to the AHA statement, published in the Association’s peer-reviewed journal Arteriosclerosis, Thrombosis, and Vascular Biology.
NAFLD occurs when abnormally elevated amounts of fat are deposited in the liver, sometimes resulting in inflammation and scarring. The prevalence of NAFLD is an estimate, given the challenges in diagnosing the condition, which are detailed in the statement.
An AHA scientific statement is an expert analysis of current research and may inform future guidelines. Professional organisations specialising in gastroenterology have previously published statements on the condition; however, they focus on liver toxicity (including scarring, cirrhosis and liver cancer) rather than heart disease risk. This is the Association’s first statement about NAFLD.
“Non-alcoholic fatty liver disease (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 Dr P. Barton Duell, FAHA, chair of the statement writing committee and professor of medicine in the Knight Cardiovascular Institute and Division of Endocrinology, Diabetes and Clinical Nutrition at Oregon Health & Science University in Portland, Oregon.
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). Excess alcohol intake can cause similar fat deposits and liver dysfunction, so the term NAFLD is used to differentiate between disease caused by excess alcohol intake versus disease without alcohol as the underlying cause.
NAFLD may go undiagnosed for years, so the statement emphasises the need for awareness and monitoring for NAFLD; access to improved screening tools and treatment, and highlights the lifestyle changes to help prevent and treat the disorder.
NAFLD raises heart disease risk
Heart disease is the leading cause of death in people with NAFLD. 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 higher risk of heart disease than people who have the same heart disease risk factors without the liver condition.
NAFLD may sometimes be prevented
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. Genetic factors also play a role in whether a person develops NAFLD and whether it leads to NASH, cirrhosis or liver cancer.
“Although healthy living can help avert NAFLD in many individuals, some may develop NAFLD despite their best efforts,” Duell said. “At the other end of the spectrum, some people may have a genetic makeup that protects them from developing NAFLD despite having obesity, Type 2 diabetes, metabolic syndrome, unhealthy dietary habits or being sedentary.”
NAFLD can go undiagnosed for years
Most people with NAFLD are undiagnosed, creating a barrier to optimal medical management, according to the statement. The initial stages of NAFLD generally have no symptoms and people feel well, and routine blood tests may not show liver abnormalities. Often, elevated liver enzymes in 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.
“The lack of awareness of the high prevalence of NAFLD contributes to under-diagnosis,” said Duell. “Individuals with risk factors for NAFLD warrant more careful screening.”
If diagnosed in time, liver damage may be reversible
“Part of the good news about managing NAFLD is that healthy eating, regular exercise and weight loss or avoiding weight gain are all valuable interventions to improve health in most of us, regardless of whether we have NAFLD,” said Duell.
Lifestyle changes are the cornerstone of treatment for early NAFLD. Dietary recommendations include reducing fat intake, limiting the consumption of simple sugars and choosing more fibre-rich vegetables and whole grains.
A Mediterranean-style diet is the only specific dietary pattern recommended by a consortium of professional groups for the treatment of NAFLD and NASH. Avoiding alcohol is encouraged since even light alcohol intake can aggravate NAFLD and interfere with the liver’s ability to heal.
Consultation with a dietitian may help people with NAFLD plan and maintain a healthful diet and lose weight, if needed. The statement cites research showing that losing 10% of body weight dramatically reduced liver fat and improved fibrosis, with lower levels of improvement with at least a 5% loss in body weight. Research also supports 20-30 minutes of physical activity per day to decrease liver fat and improve insulin sensitivity even in the absence of weight loss.
Medications may be needed to treat Type 2 diabetes, lower cholesterol or reduce weight. Weight loss surgery may be appropriate for some people because the resulting, marked weight loss can be an effective intervention for NAFLD. Optimal care may also involve consulting with a lipid specialist, endocrinologist or gastroenterologist.
This scientific statement was prepared by the volunteer writing group on behalf of the American Heart Association’s Council on Atherosclerosis, Thrombosis and Vascular Biology; the Council on Hypertension; the Council on the Kidney in Cardiovascular Disease; the Council on Lifestyle and Cardiometabolic Health; and the Council on Peripheral Vascular Disease.
Study details
Nonalcoholic Fatty Liver Disease and Cardiovascular Risk: A Scientific Statement From the American Heart Association.
P. Barton Duell, Francine Welty, Michael Miller, Alan Chait, Gmerice Hammond, Zahid Ahmad, David Cohen, Jay Horton, Gregg Pressman, Peter Toth.
Published in Arteriosclerosis, Thrombosis, and Vascular Biology on 14 April 2022
Abstract
Nonalcoholic fatty liver disease (NAFLD) is an increasingly common condition that is believed to affect >25% of adults worldwide. Unless specific testing is done to identify NAFLD, the condition is typically silent until advanced and potentially irreversible liver impairment occurs. For this reason, the majority of patients with NAFLD are unaware of having this serious condition. Hepatic complications from NAFLD include nonalcoholic steatohepatitis, hepatic cirrhosis, and hepatocellular carcinoma. In addition to these serious complications, NAFLD is a risk factor for atherosclerotic cardiovascular disease, which is the principal cause of death in patients with NAFLD. Accordingly, the purpose of this scientific statement is to review the underlying risk factors and pathophysiology of NAFLD, the associations with atherosclerotic cardiovascular disease, diagnostic and screening strategies, and potential interventions.
See more from MedicalBrief archives:
Bariatric surgery in NAFLD and obesity slashes liver and cardiovascular risk
Post-menopausal women at higher risk of NAFLD — research review
MAFLD: A new name and definition bringing hope for patients with fatty liver disease
NASH has 50% higher death rate than NAFLD
NAFLD promotes coronary artery calcification