Research articleOccupational Sitting Time and Overweight and Obesity in Australian Workers
Introduction
One of the major immediate and long-term health issues in modern society is the problem of overweight and obesity. The burden of overweight and obesity includes increased risk of premature death and chronic disease,1 as well as a reduction in the overall quality of life.2 Obesity has been identified as a risk factor for numerous chronic diseases, including type 2 diabetes, coronary heart disease, high blood pressure, stroke, and certain forms of cancer.1 In 2000, the World Health Organization estimated the number of obese adults in the world to be more than 300 million.3 In Australia, recent data show a 28% increase in the prevalence of overweight and obesity through the decade of the 1990s, with 58% of men and 42% of women now classified as overweight or obese.4, 5
The causes of overweight and obesity are often varied and complex but, at a population level, have generally been attributed to energy imbalance—as a society we are expending less energy than we are taking in.6, 7, 8 Although logical to attribute the increased prevalence of overweight and obesity to reduced physical activity levels, most population data indicate that activity levels—especially leisure-time physical activity levels—are not changing sufficiently to explain the current increases in overweight and obesity.9, 10 In any event, the emphasis on leisure-time physical activity levels may not accurately reflect the estimation of total energy expenditure at a population level. Studies that have attempted to imitate the energy expenditures of previous generations, either through the study of historical replications11 or by study of groups who use traditional methods for farming and tilling the land12 conclude that there has been a large decline in total physical activity in most developed countries over the past century. It would appear therefore that this decrease reflects increasing sedentary time during nonleisure (work) time.
In one of a small number of large-scale studies that have focused simultaneously on the measurement of both physical activity and sedentary behaviors, Martinez-Gonzalez et al.13 found evidence of the independent contributions of sedentary time and leisure activity to obesity in 15,239 men and women from 15 member-states of the European Union. In a smaller Australian study involving 185 mostly professional workers, and 529 mothers with young children, average total daily sitting time among those in full-time paid work was 8.2 hours, of which 4.2 hours was spent sitting at work.14 In this study, higher total daily sitting time was associated with a 68% increase in the odds of having a body mass index (BMI) >25. This association was no longer significant after adjustment for leisure-time physical activity, gender, and work pattern.
Recent research has reported that occupational physical activity varies across occupational categories. Using objectively measured physical activity during working hours, Steele and Mummery 15 noted significant differences between professional and blue-collar workers in terms of daily step patterns, with individuals in professional occupations reporting significantly fewer steps. This and other similar research in the area of occupational activity,16, 17 shows the need to study work-related activity and its association with overweight and obesity.
Other research into sedentariness as a determinant of overweight and obesity has tended to focus only on sedentariness during leisure time. Since leisure-time sitting represents only about one third of daily sitting time, it is not surprising that these studies have presented mixed results. While several studies have demonstrated significant associations between time spent watching TV and BMI,18, 19, 20 others have found complex relationships with, for example, children who watch the greatest amounts of TV also reporting the highest levels of participation in physical activity,21 with no significant relationships between sedentariness and BMI. There remains a need to investigate the association between sedentary behavior at work and BMI.
Very few studies have focused on the independent effect of time spent sitting at work on overweight and obesity. In light of the increasing number of hours now being spent at work by the majority of working Australians,22 the main purpose of this study was to explore the relationships between occupational sitting time and overweight and obesity in a randomly selected sample of Australian adults in full-time employment.
Section snippets
Design
Cross-sectional self-report data were obtained in September 2003 by means of computer-assisted telephone-interview (CATI) survey in two regional communities in Queensland, Australia. This study reports on data from 1579 individuals who reported full-time employment at the time of the study, out of a total of 2469 participants.
Sample
A two-stage stratified sampling design was used to randomly select households and individuals in the two target communities. Calls were made to 5611 eligible households in
Results
Overall, 2469 respondents provided data for analysis, a response rate of 44.0%. Of these, 1579 respondents reported being in full-time employment at the time of the survey. This subsample was used for the subsequent analyses.
Descriptive statistics for occupational sitting time (minutes) are shown for the entire sample, and by gender in Table 1. The overall average occupational sitting time was >3 hours/day, with 25% of the sample reporting >6 hours/day sitting at work. Average daily sitting
Discussion
A potential source of overweight and obesity in the general population is an energy imbalance in favor of intake over expenditure. There remains a need to better understand the areas where opportunities for energy expenditure are being lost in modern society. In terms of physical inactivity, the participants in this study reported an average daily occupational sitting time of >3 hours. At a univariate level, this proxy measure of inactivity was significantly higher among overweight/obese
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