Pitt researchers link obesity and sedentary lifestyle

By Annemarie Carr / Staff Writer

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A new Pitt study suggests health researchers should study not only an obese person’s physical activity but also their downtime.

Wendy King, a researcher in Pitt’s Graduate School of Public Health, measured sedentary behavior in severely obese adults. King found that researchers can most accurately predict adverse health effects if they measure obese people’s activity in 10-minute increments as opposed to a 30-minute threshold. Ten minutes of sedentary behavior, according to the study, leads to increased risk for negative health effects associated with obesity.

The study was a statistical analysis of a long-term bariatric surgery study that took place between February 2006 and February 2009 and will appear in the American Journal of Preventative Medicine in March. The researchers conducted the statistical analysis at Pitt, but the original bariatric surgery study took place at 10 different hospitals across the United States.

Of the 927 obese people analyzed, only one-third engaged in moderate to vigorous physical activity in bouts of at least 10 minutes. Seventy-nine percent of the people analyzed were women, and their median age was 45. The study considered a person obese if they had a body mass index of 30 or greater and classified people with a BMI greater than 35 as severely obese.

According to the study, which the National Institute of Diabetes and Digestive and Kidney Diseases funded, obese and severely obese people were more likely to show signs of metabolic syndrome, higher blood pressure and a greater waist circumference than subjects who were sedentary for one minute and subjects who were sedentary for 30 minutes.

King hopes these results will help change physical activity guidelines for obese adults, who make up two-thirds of all American adults, according to the National Institute of Health. Currently, activity guidelines only account for activity recommendations and do not include guidelines for sedentary behavior.

“We found that there is a great deal of variation in sedentary behavior in this population,” King said. “This variation helped explain differences in likelihood of diabetes and metabolic syndrome.”

According to the NIH, metabolic syndrome is a group of factors that increase the risk for heart disease, stroke, diabetes and other illnesses.

Jia-Yuh Chen, a graduate student who worked on the statistical analysis, said the original study involved an ankle monitor to measure the number of steps taken each minute to record sedentary behavior in one-, 10- and 30-minute bouts.

According to Chen, one to 10 minutes of sedentary time strongly correlated with metabolic syndrome, while 10 to 30 minutes of sedentary time correlated to diabetes and waist circumference.

“Our findings suggest a minimum duration of 10 minutes is preferable to one or 30 minutes for establishing sedentary time, in relation to most measures of cardiometabolic health,” Chen said in an email.

Although King does not expect people to be active all day, King said, for obese adults, just 10 minutes of watching TV, sitting at a computer or reading for a short time can lead to negative health effects.

“For every hour per day participants spent in sedentary bouts of at least 10 minutes, their odds of having diabetes increased by 15 percent, metabolic syndrome by 12 percent and elevated blood pressure by 14 percent, and their waist circumference was a half inch larger,” King said.

The study said even replacing sedentary activities with low-intensity physical activities, such as walking and stretching, can improve cardiovascular and metabolic health of severely obese adults, who make up 15 percent of the U.S. population.

“Those affected generally have difficulty meeting physical activity recommendations, which focus on moderate-to-vigorous intensity physical activity, and are at high risk of cardiovascular and metabolic disease and premature mortality,” King said.

John Jakicic, director of Pitt’s Physical Activity and Weight Management Research Center, works with obese and overweight patients and studies several types of physical activity and weight loss strategies.

“While we find in non-surgical patients that reducing sedentary behavior is important, engaging in moderate to vigorous physical activity is more predictive of weight-loss success,” Jakicic said.

The NIH recommends adults get at least 150 minutes of exercise per week, stating on its website that as little as 60 minutes of exercise a week can have health benefits.

“Of those that did, the median level was 35 minutes per week, well below the national recommendation of at least 150 minutes per week,” King said.

King said clinicians should still encourage patients with obesity do moderate-to-vigorous-intensity physical activity, which the study defined as any activity with a cadence of 80 steps per minute, for at least 150 minutes per week.

“They should also stress that some physical activity is better than none,” King said.

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