Prolonged sitting may up heart disease risk in postmenopausal women

Longer sitting time is associated with greater levels of cardiometabolic risk biomarkers among postmenopausal women who are overweight or obese, a study finds.

In the multicohort study, 518 postmenopausal women (mean age 63 years, mean BMI 31.4 kg/m²) underwent objective measurements of their sitting behaviours using an accelerometer. The data collected were then processed using machine-learning algorithms into total daily sitting time and duration of uninterrupted sitting. [J Am Heart Assoc 2020;doi:10.1161/JAHA.119.013403]

Overall, longer total daily sitting time was associated with significantly higher levels of cardiometabolic risk factors. With each additional hour of sitting duration, there were 1.24 percent increase in BMI (p=0.002) and 1.67 percent increase in waist circumference (p=0.005), after adjusting for multiple variables.

Having prolonged uninterrupted sitting time also showed similar associations: BMI increased by an average of 1.26 percent (p=0.031) while waist circumference increased by 1.80 percent (p=0.034) for every extra hour of uninterrupted sitting time.

Each additional hour of total daily sitting time and uninterrupted sitting time were both associated with 4.60 percent (p=0.015) and 6.02 percent (p=0.031) increase, respectively, in insulin resistance.

“We were surprised to observe such a strong negative link between the amount of time spent sitting and insulin resistance, and that this association was still strong after we accounted for exercise and obesity,” said principal investigator Professor Dorothy Sears from the Arizona State University College of Health Solutions in Phoenix, Arizona, US.

The researchers also stratified the analysis by Hispanic vs non-Hispanic ethnicity, which showed that Hispanic women spent significantly less time in total daily sitting (p<0.001) and in uninterrupted sitting (p=0.02) than non-Hispanic women.

“Although total daily sitting time and … duration [of uninterrupted sitting] was shorter in Hispanic women compared with non-Hispanic women in our population sample, the association between [uninterrupted] sitting … and fasting glucose concentration was significantly stronger among Hispanic women than non-Hispanic women,” noted Sears and colleagues.

For each 15-minute additional time in uninterrupted sitting, Hispanic women saw an almost 5 percent increase in fasting blood glucose levels compared with <1 percent increase in non-Hispanic women (p-interaction=0.03).

“Traditionally, clinicians focus on encouraging their patients to exercise more and increase physical activity with little focus specifically on sitting time,” the researchers urged. “Clinicians and other healthcare providers should encourage patients to reduce their sitting time intervals, in addition to encouraging physical activity.”

Prolonged uninterrupted sitting should also be avoided by taking breaks in between sitting times or replace sitting time with standing or light physical activity for brief periods, advised Sears.

“Reducing sitting time improves glucose control and blood flow, and engaging in physical activities, even light-intensity daily life activities like cooking and shopping, show favourable associations with reduced mortality risk and prevention of heart disease and stroke,” she added.