Inactivity in childhood may cause early liver damage in adulthood

Children who spend more than six hours a day sitting have a significantly increased risk of developing severe fatty liver disease and cirrhosis by early adulthood, according to a new study. The study results will be presented at the annual meeting of the Endocrine Society ENDO 2024 in Boston, Massachusetts, and published in the journal Nature's npj Gut and Liver.

“We found that the association between sedentary lifestyle and liver damage is likely to be causal,” said lead researcher Professor Andrew Agbaje, MD, MPH, PhD, from the University of Eastern Finland in Kuopio, Finland..

“The public needs to be aware of this danger of a sedentary lifestyle to the health of children, adolescents and young adults,” added Agbaje, who also works at the University of Exeter in England. “Advanced fatty liver disease and cirrhosis, which are severe scarring and hardening of the liver, may increase the risk of future liver cancer or require a transplant.”

Fatty liver disease is the harmful accumulation of fat in the liver. When this condition is not associated with alcohol consumption, but is associated with one of the components of metabolic syndrome, it is called metabolic associated steatotic liver disease (MASLD).

For this study, Agbaje analyzed data from a long-term study of a large birth cohort in the UK called the Avon Longitudinal Study of Parents and Children (ALSPAC) or "Children of the '90s." The study included 2,684 children whose movements were repeatedly measured using a belt-worn accelerometer from 11 to 24 years of age. At ages 17 and 24 years, participants underwent liver ultrasound to evaluate fatty liver disease and the presence of liver scarring. They also took blood tests to measure liver enzyme levels.

On average, the children in the study spent 6 hours a day sitting or being sedentary, but by early adulthood this increased to 9 hours a day. As children, they engaged in light-intensity physical activity 6 hours a day, which neutralized the harmful effects of 6 hours of sitting.

For every half hour of sedentary behavior over 6 hours a day, children had a 15% increased risk of developing fatty liver disease up to age 25. Increased sedentary time resulted in a 3-hour decrease in time spent in light-intensity physical activity by early adulthood. However, every additional half hour of light-intensity physical activity beyond 3 hours a day reduced the likelihood of severe fatty liver disease by 33%.

“We believe that this change in the time of sedentary behavior compared to the time of light-intensity physical activity creates the preconditions for the onset and progression of the disease,” Agbaje emphasized.

The prevalence of MASLD was 1 in 40 participants (2.5 percent) at age 17 years and 1 in 5 participants (20 percent) at age 24 years. Agbaje called the finding surprising because the risk of MASLD increased eightfold in just seven years, and a 20 percent prevalence of the disease is not typically seen until the mid-40s.

Half of 24-year-olds with MASLD had severe disease, or significant amounts of excess fat in the liver. One in every 40 young people already had signs of liver scarring, with three in 1,000 young people meeting diagnostic criteria for cirrhosis.

However, he found that participating in light-intensity physical activity for at least 3 hours a day reversed premature liver damage. Each additional minute of moderate to vigorous physical activity per day was associated with a small reduction in the odds of severe MASLD at age 24 years, but had no effect on the odds of developing cirrhosis.

“The most effective treatment for the damaging effects of childhood sedentary behavior is unadvertised 60 minutes of moderate-to-vigorous intensity physical activity per day,” Agbaje said. “Rather, it is physical activity of light intensity lasting 3-4 hours a day.”

Examples of light intensity physical activity include playing outside, playing on the playground, walking the dog, running errands for the parents, or walking and biking.