Getting adults in European countries to be at least moderately physically active could prevent over 600,000 premature deaths in Europe each year, according to research in 2015. Yet most people fall short of recommended amounts of physical activity. As well as exercising more, reducing the amount of time spent sitting down may be beneficial. In Part 2 of this article, we look into a study that found that higher amounts of sedentary (sitting) time were linked with worsened liver health.
Risks of Sitting
In our last post, we talked about how extended amounts of sitting come with increased health risks, including higher rates of dying prematurely, higher risks of cardiovascular events and most notably, approximately 100% higher risk of type 2 diabetes. Closely related to diabetes is the metabolic syndrome, a group of risk factors that includes high body weight and low HDL (“good”) cholesterol. An increase in liver fat content is believed to be a contributing factor to the development of this syndrome.
Researchers in the UK conducted a study in 2018 to see how both sitting time and exercise were related to the presence of metabolic syndrome and liver fat. Participants in the study wore activity monitors to record their levels of exercise and sedentary time. They also completed a fitness test and had an MRI scan to look at their levels of liver fat. So what did the research team find?
There were no differences in exercise habits among people who were deemed to have metabolic syndrome, versus those who didn’t. Similarly, there were no differences in the amount of time that people with the metabolic syndrome spent sitting, versus those without the syndrome. However, those with higher amounts of sitting time did have higher levels of liver fat. Each extra 60 minutes of sedentary time was associated with a 1.15% higher level of liver fat. This is significant as a liver fat content of 5.5% is the level considered to represent non-alcoholic fatty liver disease. These higher liver fat levels may represent the early stages of metabolic syndrome, even if the syndrome was not fully developed. In contrast, those with higher levels of fitness had lower levels of liver fat.
Another study looking at the relationship of sitting time with risk of the metabolic syndrome found that those who spent the least amount of time in lengthy periods of sitting (defined as more than 30 minutes of uninterrupted sitting) had less than half the odds of developing the syndrome, versus those with more uninterrupted sitting. Total time spent in sitting was not relevant, but time in lengthy (uninterrupted) periods was.
A third study in this area found that sitting time was associated with higher amounts of liver, visceral, and total abdominal fat. In this study, every 60 minutes of sitting was associated with an extra 1.8 litres of abdominal fat, but only among people who didn’t reach the recommended levels of exercise (150 minutes or more per week).
So, what we can take out of all of this? One trend is that higher levels of exercise seem to protect against the dangers of lots of sitting. However, some studies have found that it took an hour per day to eliminate all of the risks involved, which may be unrealistically high for many people. Exercise is an important part of the equation, but it may not be enough on its own except at high levels such as an hour per day.
The other big recommendation seems to be to limit uninterrupted periods of sitting. That means breaking up sitting with movement at regular intervals, such as a few minutes of standing or walking every hour. This is shown to control blood sugar levels better than uninterrupted sitting does, and on that basis it may protect against things like metabolic syndrome and diabetes. If regular movement breaks are not an option for you because of the nature of your work, the best strategy may be to stand for a period of the day. Some sources recommend standing for two hours each day to begin with, as a method of reducing sitting time. If neither movement breaks nor standing are a realistic option, the best approach is probably to make sure to exercise for an hour per day to compensate.