Environmental Factors in NAFLD/NASH
Dietary components, inadequate amounts of exercise, and sleep must also be considered as pathogenetic factors. The most effective methods of management of patients with NAFLD are based on lifestyle interventions to improve all 3.
Shahzad and colleagues proposed that increased consumption of polyunsaturated fatty acid (PUFA) might be associated with NAFLD. They studied adults participating in the Third National Health and Nutrition Examination Survey (NHANES III) who were identified as having NAFLD. Total PUFA intake and linoleic acid consumption were found to significantly increase the risk for NAFLD, especially in the Mexican American population.
Fructose overconsumption in Western diets has also been linked to NAFLD. In animal models, high fructose intake leads to metabolic disturbances that can result in chronic low-grade inflammation and the development of type 2 diabetes and cardiovascular disease.
Kienbacher and colleagues suggest that excess intake of fructose may affect the gut-liver axis by increasing intestinal permeability, bacterial translocation, and inflammation. Fructose overconsumption can act as a "hepatotoxin," serving as a second hit in those with preexisting metabolic diseases or a genetic predisposition, such as the PNPLA3 genotype.
Little is known about the optimum duration and intensity of physical activity. Long and colleagues examined the association between objectively measured activity using accelerometry and fatty liver in a cross-sectional study of participants in the Framingham Heart Study.
On average, participants engaged in 27 minutes daily of moderate to vigorous physical activity. After adjustment for age, increasing activity was associated with lower BMI and reduced steatosis. Each 30-minute-per-day increase in physical activity reduced the odds of fatty liver by 60%. For participants who met the national physical activity recommendations of engaging in at least 150 minutes per week of moderate to vigorous activity, the odds of fatty liver was reduced by 49% compared with those who did not meet these recommendations.
The duration and quality of sleep affect metabolic and histologic features in patients with NAFLD. Kochhar and colleagues analyzed 689 adult patients with a clinical diagnosis of NAFLD and uncovered sleep deprivation in 36%, sleep difficulty in 67%, and sleep apnea in 41%. Sleep apnea was associated with an increased BMI and an increased risk for diabetes, hypertension, steatosis, and possibly fibrosis.
Medscape Gastroenterology © 2014 WebMD, LLC
Cite this: William F. Balistreri. Advances in Liver Disease - Medscape - Jun 19, 2014.