The impact of screen time on cardiovascular disease, cancer incidence and mortality may be greatest in people who have lower levels of grip-strength, fitness and physical activity, according to a study published in the open access journal, BMC Medicine.

Researchers at Glasgow University, UK, found that the amount of leisure time spent watching a television or computer screen had almost double the impact on the risk of mortality, cardiovascular disease and cancer in people with low grip strength or low fitness levels than on participants who had the highest levels of fitness and grip strength. Increasing strength and fitness may offset the adverse health consequences of spending a large proportion of leisure time sitting down and watching a screen, according to the authors.

Dr Carlos Celis, corresponding author of the study said: "Our study shows that the risks associated with sedentary behaviour are not the same for everyone; individuals with low physical activity experience the greatest adverse effects. "This has potential implications for public health guidance as it suggests that specifically targeting people with low fitness and strength for interventions to reduce the time they spend sitting down may be an effective approach."

The authors suggest that measuring grip strength could be an efficient way to target individuals that may benefit most from public health interventions to reduce screen time.

Dr Celis explained: "While fitness testing can be difficult in healthcare and community settings, grip strength is a quick, simple and cheap measure, therefore it would be easy to implement as a screening tool in a variety of settings."

The study analysed data from 391,089 participants from the UK Biobank, a large, prospective, population-based study that includes data on all-cause mortality, cardiovascular disease and cancer incidence, along with screen time, grip strength, fitness and physical activity.

The researchers caution that the use of self-reported screen time and physical activity data may have impacted on the strength of the associations drawn in this study. The observational nature of the study does not allow for conclusions about cause and effect.