Prolonged physical inactivity leads to increased insulin resistance, which is a risk factor for diabetes and heart disease. Scientists at the University of Alabama at Birmingham (UAB) are exploring the perils of a sedentary lifestyle and how much inactivity is necessary to cause health problems.
“We know physical activity is beneficial for human health,” said Krista Casazza, Ph.D., assistant professor in the Department of Nutrition Sciences. “We are just discovering that physical inactivity itself can be detrimental to human health in many ways.”
Casazza is enrolling overweight girls between 7 and 11 years of age in a study to look at the impact of physical inactivity on insulin resistance and inflammation.
Changes in insulin sensitivity leading to insulin resistance happen quickly in adults and even more quickly in children. Sedentary adults — those confined to bed rest, for example — become insulin-resistant in about four days. Children will see a marked increase in insulin resistance in just one day.
Some of the girls in Casazza’s study will spend a full day completely inactive. They will spend 10 hours, from 7 a.m. to 5 p.m., seated or lying down, watching movies or reading with limited breaks to get up and move about. They will be fed three meals, with a total of 1,600 calories.
A second group will spend the same amount of time standing while engaging in mild physical activity, such as walking and stretching, with the same diet. A third group will be seated throughout the day, but will have a reduction in calorie intake of 500 calories.
All three groups will return the following day for measurements of insulin resistance and the presence of inflammatory markers. Low-grade inflammation is a by-product of inactivity, according to Casazza.
“Using the body’s muscles in physical activity releases proteins called myokines, which have anti-inflammatory properties,” Casazza said. “The opposite effect is associated with sedentary behavior, as the body releases pro-inflammatory proteins from fat cells called adipokines.”
The link between sedentary behavior and inflammation was first seen in long-haul truckers who sit for hours in their cabs. As a group, truck drivers have high rates of inflammation and a high incidence of diabetes.
Casazza hypothesizes that the simple act of standing rather than sitting will boost the production of myokines and inhibit the production of adipokines.
“Thirty minutes of exercise a day — while beneficial — is less effective if we spend the remaining 23 hours and 30 minutes of each day in a sedentary state,” Casazza said. “Perhaps the simple act of standing up from time to time throughout the day will be beneficial for schoolchildren or office workers who spend all day at their desks.”