The more time middle-aged men and women spend sitting, the greater the likelihood they will show nonalcoholic fatty liver disease on ultrasonography at an annual physical examination, according to a report published online.
While this association may not be surprising, the fact that it remained robust regardless of an individual’s level of exercise and independent of his or her body mass index (BMI) was unexpected. Even adults with a BMI less than 23 kg/m2 and even those who exercised vigorously several times per week were more likely to develop nonalcoholic fatty liver disease (NAFLD) if they spent a substantial part of their day sitting down. So it appears that both increasing physical activity and reducing sitting time are important in reducing NAFLD risk, said Seungho Ryu, M.D., of the department of occupational and environmental medicine, Kangbuk Samsung Hospital, Seoul, and associates.
The investigators discovered the association between sitting and NAFLD in a large observational cohort study involving 72,914 Korean men and 66,142 Korean women undergoing routine annual physical examinations at two academic clinics during a 2-year period. These study participants (mean age, 39.9 years) answered questionnaires regarding the average time they spent sitting at work, home, and leisure, as well as their usual dietary intake and typical level of physical activity.
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Sitting time was positively associated with the prevalence of NAFLD, independently of physical activity level. The prevalence ratios for the disorder were 1.05 for sitting 5-9 hr/day and 1.12 for sitting 10 hr/day or more, compared with the reference category of sitting for fewer than 5 hr/day. And the prevalence of NAFLD rose in a linear fashion with increased sitting time across all categories of physical activity, Dr. Ryu and associates said (J. Hepatol. 2015 Sep 15 [doi: 10.1016/j.hep.2015.07.010]).
The mechanism underlying this association is not yet known. A causal relationship cannot be assumed on the basis of these findings because this was a cross-sectional observational study, not a longitudinal or prospective randomized study. However, it seems reasonable that in real-world practice, replacing periods of sitting with periods of standing and light activity would be helpful to reduce the risk of NAFLD, they added.
The investigators noted that these study participants were all Korean, were well educated, and attended health examinations regularly, so the study results may not be generalizable to other populations with different demographic profiles.
The sources of funding for this study weren’t identified. Dr. Ryu and associates reported having no relevant financial disclosures.