A large-scale study of 15.239 people was carried out in the European Union to determine the relationship between sedentary behaviour and obesity. 15 different countries were studied to avoid cultural bias in the sample.  The sample was a stratified cluster sample - that is, stratified for each of the 15 countries chosen - made up of males and females ages 15 and older.

The study was a structured interview carried out by professional interviewers in the homes of the participants. The participants were asked about the amount of time they spend in various physical activities.  Sedentary lifestyle was assessed by self-reported hours spent sitting down during leisure time.  In addition, BMI measurements were calculated.

The researchers found a direct correlation between those who had high amounts of sedentary time (35 hours per week) and obesity and an inverse correlation between those with high amounts of physical time and obesity.

Vandelanotte et al wanted to investigate the potential negative impact of increased Internet and computer use on health.

The sample was made up of 2650 adults living in Adelaide, Australia.  The participants were asked to complete a mail-back questionnaire including items on their height and weight, past seven-day recall of leisure-time physical activity, Internet and computer use, and other leisure-time sedentary behaviours. Leisure-time Internet and computer use were categorized into no use, low use (less than three hours per week), or high use (three hours or more per week).

On average, participants with low leisure-time Internet and computer use, were less sedentary than those with high computer use.  Participants with a high leisure-time Internet and computer use were 1.46 times more likely to be overweight and 2.52 times more likely to be obese, compared to those who reported no Internet and computer use in their leisure time .  Adults with high leisure-time Internet and computer use were more likely to be overweight or obese even if they were highly active in their leisure time.

These findings suggest that, apart from nutritional and physical activity interventions, it may also be necessary to decrease time spent in sedentary behaviours, such as leisure-time Internet and computer use, in order to reduce the prevalence of overweight and obesity.

• The EU study was a stratified cluster sample, attempting to guarantee the representativeness of the sample.
• Structured interviews are highly standardized; this makes it easier to carry out the interviews, quantify the data and carry out a systematic analysis of the data.
• The studies support one another, which means that they may be generalized to theory with regard to the role of sedentary lifestyle on obesity.
• Sedentary behaviour was self-reported; this is difficult to measure and there is the potential for optimism bias.
• The BMI is considered a flawed measure of obesity.
• The study is correlational which means that cause and effect cannot be established.
• It could be argued that 3 hours of week is not “high use” of the Internet and thus could skew the results.

Martinez-Gonzalez, et al. Physical inactivity, sedentary lifestyle and obesity in the European Union.  Int J Obes Relat Metab Disord, 1999.

Vandelanotte, C,   Sugiyama, P Gardiner and N Owen. Association of leisure-time internet and computer use with overweight and obesity, physical activity and sedentary behaviours: a cross-sectional study. J Med Internet Res, 2009 Jul 27;11(3):e28. doi : 10.2196/jmir.1084.