Chronic liver disease: risk factors
Causes of Chronic Liver Disease
There are a variety of risk factors and diseases that cause chronic liver disease (CLD). The three commonest risk factors for CLD are excessive alcohol consumption; blood borne viruses, in particular Hepatitis B and C, and obesity. Risk factors can have a multiplicative effect: an individual with more than one risk factor (e.g. Hepatitis C/obesity as well as excess alcohol consumption) can further increase their risk of CLD (Corrao and Arico 2003). Metabolic disease such as haemochromatosis (which causes a build up of iron in the liver) and auto-immune disease, e.g. primary biliary cirrhosis, are relatively rare.
Alcohol is a psychoactive, potentially toxic and addictive substance. It is rapidly absorbed by the body where it is detoxified by the liver. Additional risk factors include gender (women are more susceptible), a genetic predisposition and co-occurring liver disease. Individuals consuming excess alcohol can develop alcoholic liver disease (ALD). Although a dose response effect can be observed, there is no exact level of consumption that can predict the onset of ALD nor is dependence on alcohol a pre-requisite (Gramenzi et al 2006). At a population level, the average population consumption of alcohol is closely related to mortality from CLD (Ramstedt 2003).
Blood Borne Viruses
The Hepatitis C virus is highly infectious and is transmitted through blood borne routes, principally by sharing of injecting drug use equipment, via blood transfusion (prior to instigation of blood donor testing in 1991) and, rarely, by sexual activity and mother to child transmission. One fifth of those infected with the virus recover spontaneously whilst of the remainder who develop chronic Hepatitis C infection, 5-15% will develop cirrhosis over the next 20 years [SIGN 2006].The proportion of liver-related deaths that occurred in HCV-diagnosed individuals increased from 2.8% (1995-1997) to 4.2% (2004-2006) [McDonald et al 2010].
The Hepatitis B virus is highly infectious and is transmitted through blood and bodily fluids by unprotected sex; sharing of injecting drug equipment and from mother to child transmission. Less than 10% develop chronic infection which in turn can result in CLD. It cannot be determined from routine mortality data what proportion of CLD deaths are due to Hepatitis B.
Non-alcoholic fatty liver disease (NAFLD) is a disease of the liver characterised by fatty infiltration with or without inflammation (non alcohol steatohepatitis or NASH). Previously thought to be benign, it can progress to fibrosis and cirrhosis in 15-20% of patients. It can also result in liver cancer. Development of NASH and fibrosis is associated with obesity, type 2 diabetes, hypertension and high triglycerides (Roderick et al 2004). In European and US studies, NAFLD affects 3-30% of the population, depending on whether blood tests or liver scans are the screening test (Clarke et al 2002). Deaths from NAFLD have risen in Scotland from 3 in 1979 to 40 in 2007 though this figure is likely to be an underestimate (Scottish Government 2008).