Self-reported television viewing may not be an accurate measure of total sedentary time….
Cardiometabolic abnormalities such as hypertension, central obesity, dyslipidemia and dysglycemia are known to significantly increase the risk of developing type 2 diabetes and other chronic diseases. Excessive time spent sedentary and insufficient moderate-to-vigorous physical activity (MVPA) are recognized as contributing factors to increased cardiometabolic risk.
Prior to this study, however, there was little evidence to establish a longitudinal association between the time one spends sedentary and their cardiometabolic risk. The few studies that do study this relationship have used self-reported television viewing as a marker of sedentary behavior, which does not accurately reflect total sedentary time as it is only one aspect of the total time that one spends sedentary. Therefore, its association with metabolic risk may be underestimated. While healthcare providers often recommend increased MVPA to those at high risk of T2DM, these interventions often have little success as patients experience difficulty increasing their physical activity levels. Identifying additional behavioral targets that are more manageable for these patients could help to develop new preventative interventions for future use.
A cohort analysis was performed from the ProActive trial, a trial that evaluated the efficacy of a theoretical, evidence, and family-based program that aimed to increase physical activity levels in adults at high risk for developing T2DM because of a parent with the disease. 171 of the patients in the ProActive trial were included in this cohort study, which covered a time span of 6 years. These patients were all adults, averaging 42.52 years of age ± 6.30 years.
The purpose of this study was to estimate the associations between measured time spent sedentary, time spent in MVPA, and self-reported television watching and changes in cardiometabolic risk factors. Data collection was the same at baseline and follow-up, and occurred at a study center following an overnight fast. At the study center, a venous blood sample was taken, and each participant’s fasting plasma glucose, triacylglycerol, HDL-cholesterol levels, serum insulin, waist circumference, systolic and diastolic blood pressure, weight and height were measured. These measurements were then used to compute a clustered cardiometabolic risk score (CCMR). Physical activity was measured using a piece of equipment called the ActiGraph accelerometer, which was worn by the patient for 4 consecutive days at baseline and follow-up. Sedentary time was determined by using a cutoff of <100 counts/min, and time spent in MVPA was determined using a cutoff of ≥1,952 counts/min. Time spent watching television was self-reported using a questionnaire with high repeatability and sufficient validity. Another questionnaire was completed to account for confounding variables, such as smoking status, age at finishing full-time education (used as a marker of socioeconomic status), and medication use for dyslipidemia, hypertension, or dysglycemia.
The study found that mean values for CCMR, SBP, fasting plasma glucose, fasting serum insulin, sedentary time, and television viewing time increased from baseline to the 6 year follow-up. The percentage of wear time with the ActiGraph accelerometer spent sedentary increased, and the percentage spent in MVPA decreased. Greater increase in sedentary time was independently associated with a larger increase in CCMR, triacylglycerol and waist circumference after adjusting for the relevant confounders. A greater decrease in MVPA was also associated with a larger increase in CCMR and waist circumference, as well as fasting serum insulin. These associations, though, were attenuated after adjustment for baseline and change in sedentary time, with the exception of waist circumference. A greater increase in television viewing time was also associated with a greater increase in CCMR, waist circumference, fasting plasma glucose, and fasting serum insulin, though these associations were again attenuated after adjustment for baseline and change in MVPA.
As increasing MVPA can also be particularly challenging for many patients, a more effective intervention may be to replace sedentary time with light-intensity activities that are part of daily living. This is supported by other research that demonstrates the importance of total daily physical activity rather than MVPA alone on cardiometabolic risk.
Increasing sedentary time was independently associated with increased clustered cardiometabolic risk and triacylglycerol levels.
Replacing sedentary time by light-intensity activity, thus increasing daily physical activity levels overall, could be a helpful lifestyle intervention in high-risk patients.
Wijndaele, K. et al. "Increasing objectively measured sedentary time increases clustered cardiometabolic risk: a 6 year analysis of the ProActive study" Diabetologia. 2014; 57(2): 305-313.