Non-alcoholic fatty liver disease: Prevalence and all-cause mortality according to sedentary behaviour and cardiorespiratory fitness. The HUNT Study

Purpose: Sedentary behaviour (SB) and low physical activity (PA) are independently associated with non-alcoholic fatty liver disease (NAFLD). Compared to PA, high cardiorespiratory fitness (CRF) has been associated with a higher protection against all-cause mortality and a number of specific diseases. However, this relationship has not been investigated in NAFLD. This study examined the roles of SB and CRF on: i) the likelihood of having NAFLD in the general population, and ii) the risk of mortality over 9 years within individuals having NAFLD. Methods: A cross-sectional analysis of 15,781 adults (52% female; age range 19–95 years) was conducted. Self-reported SB was divided into tertiles. CRF was estimated using validated non-exercise models, and the presence of NAFLD from the Fatty Liver Index. Adjusted Odds Ratios and 95% Confidence Intervals for NAFLD were estimated using logistic regression analyses. Hazard Ratios for all-cause mortality were estimated using Cox proportional hazard regression in individuals with NAFLD. Results: For each additional 1 h/d of SB, the likelihood of having NAFLD was significantly increased by 4% (CI, 3–6%). In combined analyses, compared with the reference group [high CRF and low (≤4 h/d) SB], individuals with low CRF had a markedly higher likelihood of having NAFLD (OR, 16.9; CI 12.9–22.3), even if they had SB ≤ 4 h/d. High CRF attenuated the negative role of SB up to 7 h/d on NAFLD. Over 9.4 ± 1.3 years of follow-up, individuals with NAFLD and low CRF had the risk of mortality increased by 52% (CI, 10–106%) compared to those with high CRF, regardless of SB or meeting PA guidelines. Conclusions: Low CRF increases the risk of premature death in individuals with NAFLD, and is strongly associated with higher likelihood of having NAFLD, outweighing the influence of SB.