Physical Activity, Television Viewing Linked to NAFLD Prevalence

Results from a cross-sectional analysis of patients from the Coronary Artery Risk Development in Young Adults (CARDIA) study are providing an overview of the association between physical activity and television viewing with prevalence of nonalcoholic fatty liver disease (NAFLD).

Increased levels of vigorous-intensity aerobic physical activity and muscle-strengthening physical activity, combined with lower levels of television viewing, were associated with a 65% reduction in risk of NAFLD relative to those with less activity and increased television viewing, with investigators noting this association occurred in a dose-response manner.¹

“The current state of evidence regarding activity levels and NAFLD has largely focused on examining the association of aerobic and muscle-strengthening physical activity in reducing the negative health impact of hepatic steatosis,” wrote investigators.¹ “Thus, investigations examining the associations of aerobic and muscle-strengthening physical activity and screen time concurrently in the same models and the risk of developing NAFLD are needed to further examine the role of physical activity and sedentary time in the etiology of NAFLD.”

An estimated 100 million individuals in the US are affected by NAFLD. Risk factors include being overweight, having obesity, and having poor eating habits. According to the American Liver Foundation, NAFLD can be prevented by maintaining a healthy weight, eating a healthy diet, and exercising regularly.²

Led by Daniel McDonough, PhD, postdoctoral research fellow, and Mark Pereira, PhD, MPH, professor, both of the division of epidemiology and community health at the University of Minnesota, a team of investigators aimed to examine the associations between physical activity, by intensity and type, and television viewing with prevalent NAFLD through a cross-sectional analysis of adults from the CARDIA study who attended the 25-year follow-up exam.¹

Among the 3499 participants of the CARDIA study, investigators selected 2726 with data related to measurements of physical activity, television viewing, and liver fat for inclusion in their analyses. Patients were excluded if they were missing this data or if they weighed more than 204 kilograms, were pregnant, had a self-reported history of hepatitis C or cirrhosis, had a risk factor for chronic liver disease, or had a potential cause of secondary hepatic steatosis.¹

The mean age of the total cohort was 50.1 (standard deviation [SD], 3.6) years and 43% of participants were male. Among the 2726 participants, 648 (23.8%) had NAFLD. Investigators noted age, education level, weekly alcohol consumption, and diet quality were similar between patients with and without NAFLD, but pointed out participants with NAFLD had greater BMI (mean 35.2 kg/m2; SD, 7.3) and waist circumference (mean 108.4 cm; SD, 14.5) than participants without NAFLD (mean 28.9 kg/m2; SD, 6.4, and mean 90.4 cm; SD, 13.6, respectively).¹

Investigators measured self-reported aerobic and muscle-strengthening physical activity using the CARDIA Physical Activity History Questionnaire at the 25-year follow-up examination, while television viewing was calculated as a weighted average of patient-reported weekday and weekend time spent watching television. Modified Poisson regression models with robust standard errors were used to estimate the adjusted risk ratios and 95% confidence intervals of NAFLD across each exposure.¹

To examine potential dose–response associations between the exposures and outcomes, we additionally constructed categorical models with the level of each exposure stratified into approximate quartiles. Model 1 was adjusted for sex, age, race, and CARDIA study center. Model 2 was additionally adjusted for education, diet, smoking status, and alcohol consumption. Models 3 and 3b were exploratory and were additionally adjusted for BMI and waist circumference, respectively.¹

Upon analysis, participants who engaged in higher levels of vigorous-intensity aerobic physical activity and lower levels of television viewing had a statistically significantly lower risk of NAFLD. Participation in 0.51–1.99 hours per week of vigorous-intensity aerobic physical activity was associated with 27% lower risk of NAFLD and ≥2 h/week was associated with 43% lower risk of NAFLD relative to 0 hours per week in Model 2. Investigators noted muscle-strengthening physical activity, relative to 0 hours per week in Model 2, was also associated with a 13% lower risk for 0–1.99 hours per week week and 22% lower risk for 2–3.99 hours per week. For television viewing, relative to <7 hours per week in Model 2, risk of NAFLD increased by 38% for 7–13.99 hours per week and by 83% for 14–20.99 hours per week. All findings were attenuated with adjustment for waist circumference in Model 3b, with only television viewing remaining statistically significant at ≥ 21 hours per week.¹

“To our knowledge, this is the first study to include physical activity, stratified by intensity and type, and television viewing in the same models to examine associations with the risk of NAFLD. Higher levels of [vigorous-intensity aerobic physical activity] and muscle-strengthening physical activity and lower levels of television viewing were associated with lower risk of NAFLD in a dose–response manner,” concluded investigators.¹

References:

1. McDonough DJ, Mathew M, Pope ZC, et al. Aerobic and Muscle-Strengthening Physical Activity, Television Viewing, and Nonalcoholic Fatty Liver Disease: The CARDIA Study. Journal of Clinical Medicine. 2023; 12(17):5603. https://doi.org/10.3390/jcm12175603
2. American Liver Foundation. Nonalcoholic Fatty Liver Disease (NAFLD). Fatty Liver Disease. Accessed September 12, 2023. https://liverfoundation.org/liver-diseases/fatty-liver-disease/nonalcoholic-fatty-liver-disease-nafld/