Risk Factors Go Up when Folks Sit Down

Sitting around too much is associated with a worsening of several cardiometabolic risk factors, an analysis of NHANES data revealed….

According to Genevieve Healy, PhD, MPH, of the University of Queensland in Australia, after accounting for several variables, including exercise, longer sedentary time was negatively associated with waist circumference, HDL cholesterol, C-reactive protein, fasting triglycerides, insulin, and measures of insulin resistance (P<0.05 for all). 

In contrast, periodically standing up and moving about for as little as a minute was associated with beneficial changes in waist circumference and C-reactive protein (P<0.05 for both), the researchers.

These findings complement and build upon previous results from smaller and/or less-diverse populations and highlight the importance of considering prolonged sedentary time as a distinct health risk behavior that warrants explicit advice in future public health guidelines. 

“While further evidence of a causal nature is required from longitudinal and intervention studies, less sitting time would be unlikely to do harm, and would, at the very least, contribute to increase overall levels of energy expenditure.” 

Several previous studies have identified a relationship between sedentary time and adverse outcomes, including death, regardless of physical activity levels. 

The study explored the issue using data from the NHANES (U.S. National Health and Nutrition Examination Survey) samples for 2003 through 2006. They included information on 4,757 adults older than 19 (mean age 46.5). All of the participants wore an accelerometer on their hip to record the amount of time spent standing or sitting still or being active. Sedentary time was defined as periods when the accelerometer read fewer than 100 counts per minute. Any interruption in sedentary time — not necessarily exercise — was considered a break. 

On average, the participants wore the accelerometer for 14.6 hours a day. Of that, 8.44 hours was sedentary time and 0.34 hours was spent exercising. The sedentary time was broken up an average of 92.5 times a day, with a mean break duration of about four minutes. 

After adjustment for potential confounders, increasing sedentary time was associated with worsening trends in several cardiometabolic markers. According to the authors, “this is consistent with plausible physiological mechanisms: fewer skeletal muscle contractions may result in reduced lipoprotein lipase activity and clearance of plasma triglycerides, reduced clearance of an oral glucose load from plasma, and less glucose-stimulated insulin secretion.” 

In addition, breaks in sedentary time were associated with beneficial changes in waist circumference and C-reactive protein levels, with particularly strong relationships with waist circumference. 

Compared with participants who had the fewest breaks, those who had the most breaks had a circumference that was 4.1 cm (1.6 inches) smaller, on average. 

The relationship with C-reactive protein suggests that inflammation may be an adjunct pathway (along with reduced muscular contractions) through which prolonged sedentary time may impact on cardiovascular disease risk. 

There was some evidence of variations in the associations between sedentary time and the cardiometabolic factors measured in gender and racial subgroups. There was an association between increasing sedentary time and HDL cholesterol in men, but not women, and between breaks in sedentary time and HDL cholesterol in women, but not men. 

The relationship between sedentary time and waist circumference was detrimental in non-Hispanic whites, inconsequential in Mexican Americans, and beneficial in non-Hispanic blacks. 

Practice Pearl: 

• Explain that a sedentary lifestyle is associated with a worsening of several cardiometabolic risk factors, including waist circumference, HDL cholesterol, C-reactive protein, fasting triglycerides, insulin, and measures of insulin resistance.
  

Healy G, et al “Sedentary time and cardio-metabolic biomarkers in U.S. adults: NHANES 2003-06” Eur Heart J 2011; DOI: 10.1093/eurheartj/ehq451.