Association of Daily Steps with Incident Nonalcoholic Fatty Liver Disease: Evidence from the UK Biobank Cohort

Abstract

Purpose: Low physical activity has been shown to be associated with a higher risk of nonalcoholic fatty liver disease (NAFLD). However, the strength and shape of this association are currently uncertain due to a reliance on self-reported physical activity measures. This report aims to investigate the relationship of median daily step count with NAFLD using accelerometer-derived step count from a large prospective cohort study.

Methods: The wrist-worn accelerometer substudy of the UK Biobank ( N = ~100,000) was used to characterize median daily step count over a 7-d period. NAFLD cases were ascertained via record linkage with hospital inpatient data and death registers or by using a measure of liver fat from imaging. Cox proportional hazards models were employed to assess the association between step count and NAFLD, adjusting for age, sociodemographic, and lifestyle factors. Mediation analyses were conducted.

Results: Among 91,031 participants (709,440 person-years of follow-up), there were 762 incident NAFLD cases. Higher step count was log-linearly and inversely associated with risk of NAFLD. A 1000-step increase (representing 10 min of walking) was associated with a 12% (95% confidence interval, 10%-14%) lower hazard of NAFLD. When using imaging to identify NAFLD, a 1000-step increase was associated with a 6% (95% confidence interval, 6%-7%) lower risk. There was evidence for mediation by adiposity, accounting for 39% of the observed association.

Conclusions: Daily step count, a modifiable risk factor, is log-linearly and inversely associated with NAFLD. This association was only partially explained by adiposity. These findings from a large cohort study may have important implications for strategies to lower NAFLD risk.

Keywords: ACCELEROMETRY; EXERCISE; PROSPECTIVE STUDIES; WALKING.

FIGURE 1

Association of quartiles of accelerometer-measured daily step count with risk of NAFLD after a median of 7.9 yr of follow-up in 91,031 UK Biobank participants. Adjusted for sex at birth, race/ethnicity, Townsend deprivation index, educational attainment, alcohol consumption, smoking status, fruit and vegetable consumption, and using age as the time scale; the number above each vertical line is the HR, and the number below each vertical line is the number of events; the dotted line shows the log-linear model.

FIGURE 2

Association of accelerometer-measured daily step count with risk of NAFLD and inclusion of potential mediators. Adjusted model: controlled for sex at birth, race/ethnicity, alcohol consumption, smoking status, educational attainment, Townsend deprivation index, fruit and vegetable consumption, and using age as the time scale. Reduction in χ² (in relation to adjusted model), quantifies the amount the observed association is due to the mediator(s). Risk mediated, quantifies the percent change in the effect estimate after addition of the mediator(s). Proportion mediated, quantifies the proportion of the total effect that is due to the mediator.

FIGURE 3

Association of quartiles of accelerometer-measured daily step count with risk of NAFLD in 15,689 UK Biobank participants with both accelerometer and imaging data. Adjusted for sex at birth, race/ethnicity, Townsend deprivation index, educational attainment, alcohol consumption, smoking status, fruit and vegetable consumption, and using age as the time scale; the number above each vertical line is the HR, and the number below each vertical line is the number of events; the dotted line shows the log-linear model.