Changes in obesity, sedentary behaviours and Perth chidren's television viewing from 1960 to 2003

Abstract

As with most of the developed world, there is clear evidence that Australian children are getting fatter. Measures of subcutaneous skinfold thickness suggest a steady linear increase in the fatness of Australian children since the mid 1970s.1,2 According to BMI measurements, the proportion of Australian children who were overweight increased by between 60-70% and the proportion of obese children more than tripled between 1985 and 1995.1,3 Various current estimates suggest that between 2327% of Australian children are currently overweight, including 6-9% who are obese.4-7 As bodyweight is regulated by numerous physiological mechanisms that maintain balance between energy intake and energy expenditure, obesity is considered a multifactorial condition with genetic and environmental predictors. Genetic factors are undoubtedly important predictors of childhood obesity, yet the rapid rise in the proportion of children in the total population who have become obese in the past 20 years is not satisfactorily explained by genetics alone; environmental factors that affect energy intake and energy expenditure are likely to have played a more significant role. Much debate surrounds the contribution of diet and physical inactivity to the rapid rise in childhood obesity. One of the most common assumptions used in the research literature is that the rise in childhood obesity has come about due to ‘increased’ sedentary use of modern media such as television and computers.812 While there is clear evidence that the amount of time spent watching television is positively related to BMI, the direction of this relationship remains equivocal.10,12-17 The contention that television viewing has contributed to the childhood obesity epidemic clearly presumes that the amount of sedentary time children spend watching television has increased since the medium was first introduced around half a century ago. To test this hypothesis, I examined a 1959-60 study of children’s out-of-school activities conducted in Perth, Western Australia18 that sampled an equal number of male and female school students aged 13-14 years from a representative cross-section of government and non-government schools. In 1959, a sample of 224 children completed a one-week, out-of-school activity diary before the introduction of television and one year later a second sample of 203 children completed the same activity diary, of which just under half (n=86) reported having televisions in their homes. The television viewing behaviours of these children are compared in Table 1 to 12-14 year-old children’s leisure activities in 2003 as suggested by the Australian Bureau of Statistics.19 From this comparison it is evident that the amount of sedentary time Perth children spend on modern media activities has changed little, if at all, in the intervening 43 years. Interestingly, ‘televiewing’ by children in 1960 appears to have largely replaced other sedentary behaviours in 1959. For example, listening to radio programs dropped from seven hours and 42 minutes per week in 1959 to only 54 minutes in 1960, and watching ‘pictures’ at the cinema dropped from three hours per week to only 48 minutes per week. This result suggests that children’s sedentary behaviours associated with the use of modern media is a poor explanation for increased childhood obesity in the past several decades. It also complements other research that suggests increased consumption of energy-dense foods, not physical inactivity, is chiefly responsible for the rapid increases observed in childhood obesity in the past 20 years.20