The Epidemiology of Nonalcoholic Fatty Liver Disease: A Global Perspective

Mariana Lazo, M.D., M.Sc.; Jeanne M. Clark, M.D., M.P.H.

Disclosures

Semin Liver Dis. 2008;28(4):339-350. 

In This Article

Sociodemographic Differences in the Prevalence of NAFLD

Gender

Although early studies emphasized that NAFLD was more common in women,[93] recent studies have shown that NAFLD has a more even distribution between men and women, or may even be more prevalent among men. The possibility that female hormones protect against NAFLD has been postulated and supported by evidence that NAFLD is twice as common in postmenopausal women as in premenopausal women. Those who receive hormone replacement therapy are significantly less likely to have NAFLD compared with women who do not.[15,94,95] Sex-related differences in fat distribution may also contribute to this finding, with women having less visceral fat than men.[96,97]

Age

NAFLD can be found in all age groups; however the prevalence appears to increase with age. A study conducted in 1977 using liver biopsy found that the prevalence of fatty liver in the general population was 1% in people below 20 years, 18% between 20 and 40 years, and 39% among 60 and older.[60] Several subsequent studies using different methods to define NAFLD have shown similar findings. In a population-based study in the United States, Browning et al found that individuals with MRS defined-NAFLD were slightly older (46 versus 45 years old, p = 0.003) than those with normal HT.[46] These findings are in agreement with studies that have shown an increasing prevalence of insulin resistance, a major risk factor for NAFLD, with age.[98,99]

Race-Ethnicity

Given the high prevalence of obesity and type 2 diabetes in African Americans compared with whites in the United States, it is conceivable that similar differences in NAFLD would be observed. However, several studies have found the contrary including a large and robust population-based study that directly measured HT and defined hepatic steatosis as HT> 5.5%. In that study, Browning et al found that African Americans have significantly less HT (median 3.2%) and hepatic steatosis (24%) than non-Hispanic whites (HT median 3.6% and hepatic steatosis 33%) or Hispanics (HT median 4.6% and hepatic steatosis 45%) even after adjusting for obesity and diabetes.[46] In another study, Caldwell et al observed that, although there was overrepresentation of African Americans among patients seen with major risk factors for NAFLD and other liver diseases, a disproportionately small fraction of patients with NAFLD were African Americans.[100] One explanation may be the ethnic differences in body fat distribution or fat metabolism, with African Americans having more subcutaneous, but less visceral fat or, as recently suggested, that African Americans have a different lipoprotein metabolism.[101]

In contrast to African Americans, studies conducted among Asians in the United States and in their countries of origin, indicate that the prevalence of NAFLD is directly related to the higher prevalence of central obesity, type 2 diabetes, and insulin resistance in these groups.[102] Furthermore, in a study using proton-MRS Peterson et al found that even after adjusting for BMI and age, Asian Indian men have significantly higher HT compared with their Caucasian counterparts (1.54 vs. 0.77%).[103]

Similar to Asians, the prevalence of hepatic steatosis among Hispanics is very high and is consistent with the increased burden of type 2 diabetes and obesity among this group.[46,66] Studies using liver enzymes as surrogates of NAFLD have also reached similar conclusions.[15,49]

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