Active Voice: Television Viewing Time Predicts Usual Walking Speed — But Is It the Sitting That’s Important?
By Victoria L. Keevil, BMBCh and Katrien Wijndaele, Ph.D.
Victoria L. Keevil, BMBCh, is a clinician specializing in medicine for older people and was awarded a Wellcome Trust clinical training fellowship to undertake a Ph.D. under the supervision of Prof Kay-Tee Khaw, at the Department of Public Health and Primary Care, University of Cambridge (UK). She is interested in the heterogeneity of physical functional health in later life and in establishing links with modifiable risk factors, including sedentary behavior. Her research was inspired by the need for evidence-based public health policy to promote good health in older age.
Katrien Wijndaele, Ph.D., is a British Heart Foundation (BHF) intermediate basic science research fellow at the Medical Research Council Epidemiology Unit, University of Cambridge (UK). Her primary research interest lies in the potential health consequences of prolonged sitting in adults and children, with an additional focus on sedentary behavior measurement and development of intervention strategies to decrease prolonged sitting.
This commentary presents Drs. Keevil’s and Wijndaele’s views on the topic of a research article which they and other colleagues had published in the April 2015 issue of Medicine & Science in Sports & Exercise® (MSSE).
Sedentary behavior, i.e., time spent sitting or lying when energy expenditure is low, has been proposed as an independent risk factor for poor health and is acknowledged in a recent ACSM Position Stand on physical activity recommendations. In particular, both total sitting time and specific sedentary behaviors, such as watching television (TV), have been associated with type 2 diabetes, cardiovascular disease, specific cancers and premature mortality. However, little is known about the potential impact of prolonged sitting on physical function. This is somewhat surprising given the established link between prolonged bed rest and muscle atrophy, the importance of maintaining optimal physical function later in life and the high volumes of sitting time observed among older adults. Therefore, sedentary behavior is potentially an attractive target for public health intervention.
In our research article published in April 2015 issue of MSSE, we utilized the infrastructure of a large prospective cohort study, the European Prospective Investigation of Cancer (EPIC)-Norfolk study, to investigate associations between television viewing time and objective measures of physical capability in community-based adults aged 48-92 years old. Television viewing time, the most common leisure time sedentary behavior in Western cultures, was measured in more than 6000 participants at two time periods: in 1998-2000 and again in 2006-2007. Usual walking speed, grip strength and timed chair stands speed also were measured at a central research clinic between 2006 and 2011. These objective measures of physical function have been extensively validated in clinical and epidemiological cohorts and usual walking speed and grip strength also are featured in the motor domain of the National Institutes for Health toolbox.
We found that men and women who watched TV for less than two hours per day, either in 1998-2000 or 2006-2007, had faster usual walking speeds compared to those who watched TV for four or more hours per day. In analyses combining men and women and using the average of both TV viewing time measurements, a clear dose-response association was evident across TV viewing time categories. Those who watched less than two hours per day walked 2.4 m/min faster than those who watched four or more hours/day, a difference in usual walking speed equivalent to around four years difference in age. TV viewing time was not consistently or strongly associated with either grip strength or timed chair stands speed, the latter being a proxy measure for lower body strength.
Usual walking speed has been proposed as the “sixth vital sign” of health in older people. It is associated with a range of health parameters, including cognition and premature mortality. Therefore, the observed association of less TV viewing time with faster usual walking speed, which persisted when TV viewing time was measured nearly a decade before, is of great public health interest. These findings add valuable evidence to the existing literature in this area, which is mainly cross-sectional and often based on self-reported measures of physical function, which come with substantially more measurement error.
We do, of course, have to carefully consider the interpretation of our findings before recommending change in public health policy. TV viewing time is not a measure of overall sitting and it is associated with a complex range of socioeconomic and behavioral factors. Although we aimed to account for these variables in our analyses, we cannot be certain that it is the “sitting” per se, while watching TV that is solely contributing to the association we observed. Future studies with objective measures of overall sitting time should explore prospective associations with physical function.