Few studies have examined the association between occupational sitting and body mass index (BMI), particularly among diverse populations, said researchers from the Washington University in St Louis.

"The objective of this study was to quantify the association between self-reported occupational sitting time and BMI by gender and race, independent of time spent in physical activity outside of work," said lead author Lin Yang, postdoctoral research associate at the Prevention Research Center, a collaboration between the School of Medicine, the Brown School and the Saint Louis University School of Public Health.

"To the best of our knowledge, this is the first study to examine differences in the association between occupational sitting and weight status among African American women and white women," Yang said.

In 2012 and 2013, participants residing in four Missouri metropolitan areas were interviewed via telephone. The interview included questions on socio-demographic characteristics and time spent sitting at work.

The researchers examined the association between occupational sitting and BMI between men and women and between black and white women.

They found that average daily time spent by both men and women in occupational sitting was between three and six hours. Most participants in the study were overweight or obese.

"After adjusting for potential confounders, we found that African-American women in three categories of sitting time (31-180 minutes, 181-360 minutes, and more than 360 minutes) were approximately and consistently 2.5 times as likely to be obese as African-American women who reported sitting for 30 minutes or less, independent of occupational and leisure-time physical activity," the researchers said.

This association was not seen among white women and no significant associations were found among men.

"The lack of association between occupational sitting and weight status among men might be explained by the differences between men and women in physical activity preferences," the researchers said.

"Men are more active in leisure-time physical activity than women and women tend to do less vigorous and more moderate activity compared with men," they said.

The results of the study were published in the journal Preventing Chronic Disease.

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