Korean Study Adds More Evidence That Exercise Doesn’t Counteract Effects of Sitting Disease

When Runner’s World Magazine ran their story Sitting is the New Smoking- Even for Runners two years ago it was the first time a mainstream publication reported on the mounting evidence that just because you run, bike, or go to the gym, sitting for too many hours a day can still wreak havoc with your body. In other words, exercise is not a cure for sitting disease. The only solution? Sitting less.

Now a new, very large, cross-sectional study just announced in Medscape Medical News has linked prolonged sitting and decreased physical activity with nonalcoholic fatty liver disease (NAFLD), even in physically active people of normal weight. The results, published this month in the Journal of Hepatology, underscores mounting evidence of the importance of reducing sedentary time and increasing physical activity to prevent chronic illnesses and premature death.

“The findings of this study suggest that both increasing participation in physical activity and reducing sitting time are independently important for NAFLD risk,” Seungho Ryu, MD, PhD, from the Department of Occupational and Environmental Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, South Korea, and colleagues write.

Dr Ryu and fellow researchers analyzed almost 140,000 Koreans from the Samsung Health Study cohort. Physical activity levels and sitting times were assessed, excluding cohort subjects with known liver disease or who had taken medications associated with NAFLD.

Study participants were grouped into three categories of sitting time: <5 hours a day, 5 – 9 hours a day, and 10+ hours a day. Their activity levels were grouped as inactive, minimally active, and health-enhancing physically active. Fatty liver was determined using ultrasound measurement. The study cohort was evenly split male/female, with a mean age of 40 and a mean body mass index (BMI) of 23—which, incidentally, is far healthier than the average 40 year old American. The mean sitting time of these participants was 7.6 hours—again, significantly less than the average American office worker sits every day.

The researchers found that 28% of the participants had NAFLD. A multivariable-adjusted model found both prolonged sitting time and decreased physical activity were independently associated with increasing NAFLD prevalence. Interestingly, these associations held even in normal-weight individuals, including those with BMIs under 23.

Notably, an adverse effect of prolonged sitting (10+ hours per day) on NAFLD emerged even among the physically active group.

“More than half of the average person’s waking day involves sedentary activities, and NAFLD is very common,” Dr Ryu told Medscape Medical News. “From the viewpoint of public health, reducing sitting time could have a substantial impact on liver metabolic health in the general population. So doctors need to educate patients not only about increasing physical activity but also about reducing time spent sitting.”

In an accompanying editorial, commentator Michael I. Trenell, PhD, a professor of metabolism and lifestyle medicine at Newcastle University, Newcastle upon Tyne, United Kingdom, adds, “The data from Ryu and colleagues add to the strong and alarming evidence that sitting too much and moving too little has significant negative consequences for cardio-metabolic health.”

He warns: “The message is clear, our chairs are slowly but surely killing us.”

We cannot agree more. The average American office worker’s BMI is far higher than the average Korean subject in this study, and we spend even more hours a day sitting – whether at our desks, in meetings, in our cars, at mealtimes, or on the sofa watching TV.

The bottom line is that you can’t unravel the effects of sitting disease just by obeying your Fitbit and getting in 10,000 steps a day and 150 minutes of vigorous exercise per week. The new study shows that while this guideline is very important for maintaining cardiovascular health, the impact of sedentariness on our spinal health, organ health, circulatory health – and productivity – is not mediated by the other things we do when we’re not working.