Jim Kling
December 6, 2011 — Nonalcoholic fatty liver disease is not associated with increased all-cause or cardiovascular mortality, according to a study published online November 18 in the British Medical Journal.
Nonalcoholic fatty liver disease is present in as much as 30% of the population and is a leading cause of chronic liver disease. It includes a number of conditions including steatosis, nonalcoholic steatohepatitis, fibrosis, and cirrhosis. It can also cause hepatocellular carcinoma and is associated with some cardiovascular risk factors.
Despite these trends, previous studies have shown inconsistent association between nonalcoholic fatty liver disease and mortality. The studies were small and either used highly selected patient populations or used liver enzyme measurements as surrogate markers for nonalcoholic fatty liver disease.
The researchers conducted a prospective cohort study using the US Third National Health and Nutrition Examination Survey (1988 - 1994), with follow-up to 2006. The study included 11,371 adults aged 20 to 74 years who were assessed for nonalcoholic fatty liver disease by the presence of moderate to severe steatosis (diagnosed by ultrasound) and normal levels of enzyme levels. Participants with steatosis and raised liver enzymes were classified as having nonalcoholic steatohepatitis. Mortality was categorized by all causes, cardiovascular disease, cancer, and liver disease.
Nonalcoholic steatohepatitis was present in 3.1% of the population, whereas nonalcoholic fatty liver disease was present in 16.4% of the participants. After adjustment for sex, race/ethnicity, education, smoking, alcohol consumption, physical activity, body mass index, hypertension, hypercholesterolemia, and diabetes, the researchers found that among participants with nonalcoholic fatty liver disease, the hazard ratio (compared with that of those patients without steatosis) for all-cause mortality was 0.92 (95% confidence interval [CI], 0.78 to 1.09). For cardiovascular disease, the ratio was 0.86 (95% CI, 0.67 - 1.12). The hazard ratio for cancer was 0.92 (95% CI, 0.67 - 1.27), and for liver disease it was 0.64 (95% CI, 0.12 - 3.59).
Participants with nonalcoholic steatohepatitis had the following adjusted hazard ratios compared with participants without stenosis: all-cause mortality, 0.80 (95% CI, 0.52 - 1.22); cardiovascular disease, 0.59 (95% CI, 0.29 - 1.20); cancer, 0.53 (95% CI, 0.26 - 1.10); and liver disease, 1.17 (95% CI, 0.15 - 8.93).
The study had several limitations, including the fact that it relied on raised liver enzymes in the presence of steatosis to define nonalcoholic fatty liver disease, rather than liver autopsies. There was no measure of change in nonalcoholic fatty liver disease over time, and some data were self-reported. In addition, follow-up time may not have been long enough to determine the association between nonalcoholic fatty liver disease and liver-related mortality.
The researchers recommend that the study be repeated in the general population, using improved, noninvasive assessment tools and finer staging of nonalcoholic fatty liver disease.
The authors have disclosed no relevant financial relationships.
BMJ. Published online November 18, 2011. Full text
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