Abstract
Children who spend a lot of time watching television have an increased risk of obesity and poor fitness as adults. It remains unclear whether childhood viewing directly impacts on adult health, or if these long-term associations are mediated by adult viewing. The objective of this study was to compare the relative contributions of childhood and adult television viewing on body mass index and cardiorespiratory fitness in a birth cohort of 1037 Study members (502 female), born in Dunedin between April 1972 and March 1973. Hours of television viewing were collected at ages 5, 7, 9, 11, 13, 15 and 32 years. Body mass index and cardiorespiratory fitness were measured at age 32 years. Time spent watching television during childhood correlated with viewing time at age 32 years (r=0.32, p<0.0001). Both childhood and adult television viewing times were associated with higher body-mass index and lower cardiorespiratory fitness at age 32 years. Childhood television viewing was a better predictor of adult obesity and poor fitness than adult viewing and remained a significant predictor of these outcomes after adjusting for adult viewing time. Specifically, for each hour of mean weekday television viewing during childhood, the odds (95% confidence interval) of adult obesity increased by a factor of 1.24 (1.01 to 1.53) and poor fitness increased by a factor of 1.40 (1.16 to 1.70). The association between childhood television viewing and obesity and poor fitness in adulthood does not appear to be mediated by adult viewing. This suggests that detrimental health effects of watching too much television during childhood persist into adulthood. Attempts to reduce adult obesity and poor fitness by modifying television viewing habits may need to begin in childhood.