Abstract
BackgroundDiscretionary screen time (time spent viewing a television or computer screen during leisure time) is an important contributor to total sedentary behaviour, which is associated with increased risk of mortality and cardiovascular disease (CVD). The aim of this study was to determine whether the associations of screen time with cardiovascular disease and all-cause mortality were modified by levels of cardiorespiratory fitness, grip strength or physical activity.MethodsIn total, 390,089 participants (54% women) from the UK Biobank were included in this study. All-cause mortality, CVD and cancer incidence and mortality were the main outcomes. Discretionary television (TV) viewing, personal computer (PC) screen time and overall screen time (TV + PC time) were the exposure variables. Grip strength, fitness and physical activity were treated as potential effect modifiers.ResultsAltogether, 7420 participants died, and there were 22,210 CVD events, over a median of 5.0 years follow-up (interquartile range 4.3 to 5.7; after exclusion of the first 2 years from baseline in the landmark analysis). All discretionary screen-time exposures were significantly associated with all health outcomes. The associations of overall discretionary screen time with all-cause mortality and incidence of CVD and cancer were strongest amongst participants in the lowest tertile for grip strength (all-cause mortality hazard ratio per 2-h increase in screen time (1.31 [95% confidence interval: 1.22–1.43], p < 0.0001; CVD 1.21 [1.13–1.30], p = 0.0001; cancer incidence 1.14 [1.10–1.19], p < 0.0001) and weakest amongst those in the highest grip-strength tertile (all-cause mortality 1.04 [0.95–1.14], p = 0.198; CVD 1.05 [0.99–1.11], p = 0.070; cancer 0.98 [0.93–1.05], p = 0.771). Similar trends were found for fitness (lowest fitness tertile: all-cause mortality 1.23 [1.13–1.34], p = 0.002 and CVD 1.10 [1.02–1.22], p = 0.010; highest fitness tertile: all-cause mortality 1.12 [0.96–1.28], p = 0.848 and CVD 1.01 [0.96–1.07], p = 0.570). Similar findings were found for physical activity for all-cause mortality and cancer incidence.ConclusionsThe associations between discretionary screen time and adverse health outcomes were strongest in those with low grip strength, fitness and physical activity and markedly attenuated in those with the highest levels of grip strength, fitness and physical activity. Thus, if these associations are causal, the greatest benefits from health promotion interventions to reduce discretionary screen time may be seen in those with low levels of strength, fitness and physical activity.
Highlights
Discretionary screen time is an important contributor to total sedentary behaviour, which is associated with increased risk of mortality and cardiovascular disease (CVD)
Using data from UK Biobank, which includes almost 500,000 participants with data on grip strength and over 60,000 participants with data on cardiorespiratory fitness, we recently reported that the adverse association of low levels of physical activity with mortality and CVD events are substantially stronger in individuals with low levels of grip strength and/or cardiorespiratory fitness
When the cohort was stratified by grip strength, the hazard ratios (HR) for mortality, CVD and cancer associated with increasing screen time were almost twice as strong in those with low compared with high levels of grip strength
Summary
Discretionary screen time (time spent viewing a television or computer screen during leisure time) is an important contributor to total sedentary behaviour, which is associated with increased risk of mortality and cardiovascular disease (CVD). Low levels of physical activity [1] and high levels of sedentary behaviour (overall sitting and discretionary television viewing and computer use) [2,3,4] both have strong associations with a number of adverse health outcomes, including mortality and cardiovascular disease (CVD). Using data from UK Biobank, which includes almost 500,000 participants with data on grip strength and over 60,000 participants with data on cardiorespiratory fitness, we recently reported that the adverse association of low levels of physical activity with mortality and CVD events are substantially stronger in individuals with low levels of grip strength and/or cardiorespiratory fitness This impies that the benefits of physical activity may be greatest amongst individuals with lower levels of functional capacity, but relatively modest in those with already high levels of functional capacity, who were at low risk irrespective of physical activity levels [9]. We hypothesised that a similar pattern would be evident for discretionary screen-time behaviours such as TV viewing and personal computer (PC) screen time, with the adverse effects of high levels of screen time being greatest in those with low levels of strength, fitness and physical activity [10]
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