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TV viewing, but not total sedentary behaviour, is associated with adverse cardiometabolic biomarkers in adolescents
  1. Stuart J H Biddle1,2,
  2. James King1,2,
  3. Thomas Yates2,3
  1. 1School of Sport, Exercise & Health Sciences, Loughborough University, Loughborough, Leicestershire, UK
  2. 2The NIHR Biomedical Research Unit in Nutrition, Diet and Lifestyle at the University Hospitals of Leicester NHS Trust and Loughborough University, Leicestershire, UK
  3. 3Department of Cardiovascular Sciences, University of Leicester, Leicestershire, UK
  1. Correspondence to Stuart J H Biddle
    School of Sport, Exercise & Health Sciences, Loughborough University, Ashby Road, LE11 3TU, Loughborough, UK; S.J.H.Biddle{at}lboro.ac.uk

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Implications for practice and research

  • Cardiometabolic biomarkers are associated with higher TV viewing and indicate a reduction in TV viewing for adolescents may be warranted.

  • TV viewing may not be a good marker of overall sedentary behaviour.

  • TV viewing may be part of wider cluster of ‘unhealthy’ behaviours.

  • In future, researchers should assess more than TV viewing when looking at sedentary behaviour.

Context

Sedentary behaviour comprises a range of sitting (and lying down) behaviours characterised by very low-energy expenditure. There has been a major increase in research interest in sedentary behaviour over the past few years and a growing concern among health and education professionals, as well as parents, that excessive ‘screen time’ might be directly affecting the health of young people by setting the preconditions for metabolic dysfunction.

Methods

Martinez-Gomez et al conducted a cross-sectional study of 183 Spanish adolescents aged 13–17 years (a subsample from the AFINOS study1). Assessments were made of total sedentary time and moderate-to-vigorous physical activity (MVPA) using accelerometry and self-reported TV viewing. Biomarkers assessed included C reactive protein, complement factors C3 and C4, interleukin-6, adiponectin, leptin, intercellular adhesion molecule 1 (ICAM-1), vascular cell adhesion molecule 1 (VCAM-1), E-selectin, L-selectin and plasminogen activator inhibitor-1. Due to their established roles in mediating inflammation and/or the development of atherosclerosis, these markers have been identified as important indicators of cardiometabolic health and risk of developing cardiometabolic disease.

Findings

Total sedentary time and TV viewing were uncorrelated suggesting that TV viewing is not a good marker of ‘overall’ sedentary time. This supports findings from a previous study.2 After controlling for confounders, sedentary time was not associated with the cardiometabolic markers whereas TV viewing was. Specifically, TV viewing time was positively associated with soluble endothelial adhesion molecules ICAM-1, VCAM-1, L-selectin and E-selectin (β 0.16–0.19, p=0.008–0.023). Adolescents watching >3 h of TV per day had higher cell adhesion molecule concentrations than those watching <1 h/day.

Commentary

Of note, total sedentary time, assessed by accerelometry, was not associated with time spent in TV viewing. It is often assumed that TV constitutes a good marker of sedentary behaviour in young people. This now appears to be in doubt. However, one might expect that it would be total sedentary time rather than TV viewing that shows adverse health trends, but the results show the opposite. This supports the view that TV viewing is not really a marker of total sedentary time but may be reflective of a cluster of other negative health behaviours and general socio-economic status. This has important implications for the assessment of individual sedentary behaviours, in so far as we should avoid single markers, such as TV viewing.

It is also important to stress that the need to look beyond the data does not only apply to self-reported measures of sedentary behaviour, but to objective measures as well. This study used one of the most commonly used objective measures of MVPA and sedentary behaviour, Actigraph accelerometers. While these are accepted in the measurement of MVPA, their use in measuring sedentary behaviour is less well defined and subject to a rapidly evolving field of research. However, there is mounting evidence that a much higher cut-point than the 100 counts/min used, in the region of 600–1100, may be a more appropriate measure of sedentary behaviour in children,3 meaning lower thresholds may not adequately distinguish between common sedentary and non-sedentary behaviours. Therefore, it is important that the data from both the objective and subjective measures used in this study are viewed in this light and that any conclusions drawn are tentative.

The associations found between TV viewing and soluble adhesion molecule biomarkers suggest that higher levels of TV might promote the development of atherosclerosis, and, subsequently, increase the risk of developing coronary and peripheral artery disease. Importantly, the associations with TV time and biomarkers are independent of MVPA, suggesting that sedentary time, or in the present study just TV viewing, is a behaviour or cluster of behaviours that requires addressing in its own right. It should not be confused with low levels of MVPA.

References

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Footnotes

  • Competing interests None.

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