Leisure time computer use and adolescent bone health—findings from the Tromsø Study, Fit Futures: a cross-sectional study
- Anne Winther1,2,
- Luai Awad Ahmed1,3,
- Anne-Sofie Furberg4,
- Guri Grimnes5,6,
- Rolf Jorde5,6,
- Ole Andreas Nilsen1,
- Elaine Dennison7,8,
- Nina Emaus1
- 1Department of Health and Care Sciences, UiT The Arctic University of Norway, Tromsø, Norway
- 2Division of Rehabilitation Services, University Hospital of North Norway, Tromsø, Norway
- 3Institute of Public Health, College of Medicine and Health Sciences, United Arab Emirates University, Al Ain, UAE
- 4Department of Community Medicine, UiT The Arctic University of Norway, Tromsø, Norway
- 5Division of Internal Medicine, University Hospital of North Norway, Tromsø, Norway
- 6Tromsø Endocrine Research Group, Department of Clinical Medicine, UiT The Arctic University of Norway, Tromsø, Norway
- 7MRC Lifecourse Epidemiology Unit, Southampton, UK
- 8Victoria University, Wellington, New Zealand
- Correspondence to Anne Winther;
- Received 17 September 2014
- Revised 25 February 2015
- Accepted 20 March 2015
- Published 22 April 2015
Objectives Low levels of physical activity may have considerable negative effects on bone health in adolescence, and increasing screen time in place of sporting activity during growth is worrying. This study explored the associations between self-reported screen time at weekends and bone mineral density (BMD).
Design In 2010/2011, 1038 (93%) of the region’s first-year upper-secondary school students (15–18 years) attended the Tromsø Study, Fit Futures 1 (FF1). A follow-up survey (FF2) took place in 2012/2013. BMD at total hip, femoral neck and total body was measured as g/cm² by dual X-ray absorptiometry (GE Lunar prodigy). Lifestyle variables were self-reported, including questions on hours per day spent in front of television/computer during weekends and hours spent on leisure time physical activities. Complete data sets for 388/312 girls and 359/231 boys at FF1/FF2, respectively, were used in analyses. Sex stratified multiple regression analyses were performed.
Results Many adolescents balanced 2–4 h screen time with moderate or high physical activity levels. Screen time was positively related to body mass index (BMI) in boys (p=0.002), who spent more time in front of the computer than girls did (p<0.001). In boys, screen time was adversely associated with BMDFF1 at all sites, and these associations remained robust to adjustments for age, puberty, height, BMI, physical activity, vitamin D levels, smoking, alcohol, calcium and carbonated drink consumption (p<0.05). Screen time was also negatively associated with total hip BMDFF2 (p=0.031). In contrast, girls who spent 4–6 h in front of the computer had higher BMD than the reference (<2 h).
Conclusions In Norwegian boys, time spent on screen-based sedentary activity was negatively associated with BMD levels; this relationship persisted 2 years later. Such negative associations were not present among girls. Whether this surprising result is explained by biological differences remains unclear.
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