research letter
Diabetes, Obesity and Metabolism 16: 1265–1268, 2014. © 2014 John Wiley & Sons Ltd
Increased physical activity is known to be beneficial in people with type 2 diabetes mellitus (T2DM), but it is not known whether individuals change their activity levels after T2DM diagnosis. The present Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial, conducted in participants with impaired glucose tolerance at high cardiovascular risk, assessed ambulatory activity annually using research-grade pedometers. Oral glucose tolerance tests were performed annually and repeated to confirm T2DM diagnosis. This observational analysis used general linear models to compare step counts before and after T2DM diagnosis in the 2816 participants with the requisite data. Participants were relatively inactive at baseline, taking a median (interquartile range) of 5488 (3258–8361) steps/day, which decreased after T2DM diagnosis by a mean (s.e.) of 258 (64) steps/day (p < 0.0001); however, after adjusting for background trend for activity, step count after T2DM diagnosis was unchanged [mean (s.e.) of 103 (87) fewer steps/day; p = 0.23]. Awareness of T2DM diagnosis had no impact on the trajectory of activity established before the diagnosis. Keyword: observational study Date submitted 19 December 2013; date of first decision 20 February 2014; date of final acceptance 20 May 2014
Introduction Increased physical activity as part of general lifestyle improvement reduces the risk of development of type 2 diabetes mellitus (T2DM) [1,2] and improves cardiovascular risk factors, although a reduction in cardiovascular events has not been shown [3,4]. The American Diabetes Association and other bodies advise that those with T2DM or impaired glucose tolerance (IGT) increase activity levels to >150 min/week [5–7]. It is unknown whether individuals increase their activity levels after T2DM diagnosis. Improved physical activity after T2DM diagnosis would suggest that lifestyle advice is being given and acted upon, or that patients are taking their own initiative, whereas absence of improvement would suggest that barriers exist to the uptake or provision of lifestyle advice. To date, no studies have examined the impact of T2DM diagnosis on activity. We investigated whether physical activity levels, measured by pedometer steps, change after T2DM diagnosis in the present Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial.
Materials and Methods Study Population The present NAVIGATOR trial (NCT00097786) was a multinational randomized, placebo-controlled, 2 × 2 factorial trial investigating the respective effects of Nateglinide and Valsartan on cardiovascular risk and new-onset diabetes in participants with IGT [8] and existing cardiovascular disease or high Correspondence to : Dr David Preiss, BHF Glasgow Cardiovascular Research Centre, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK. E-mail: [email protected]
cardiovascular risk [9,10]. Patients were enrolled between January 2002 and January 2004, and followed up for 5 years, for progression to T2DM (n = 9306). To evaluate pedometer activity before and after T2DM diagnosis, we included only patients who progressed to T2DM and who contributed pedometer data at least once before and once after T2DM diagnosis (n = 2816). All participants provided written consent. Ethical approval was obtained for the study for all sites.
Lifestyle Advice All participants took part in a standard lifestyle modification programme. One element consisted of advice to increase activity to >150 min/week. Study personnel administered the programme to all participants, who received relevant reading materials at visits within the first year (0.5, 1, 3, 6 and 12 months), with additional reinforcement through telephone contacts thereafter.
Physical Activity Habitual ambulatory activity was assessed using research-grade pedometers (Accusplit, San Jose, CA, USA). Two weeks after the baseline measurements, and annually thereafter, participants received pedometers and were instructed to wear them during waking hours for 7 consecutive days. Participants were instructed to record their daily step count in a log book and return it to the study team.
Diagnosis of T2DM During the Study Biochemical measures, including an oral glucose tolerance test, were repeated annually. Fasting plasma glucose (FPG) level was measured every 6 months for the first 3 years,
RESEARCH LETTER
Change in levels of physical activity after diagnosis of type 2 diabetes: an observational analysis from the NAVIGATOR study
research letter then annually. T2DM was defined as FPG ≥7.0 mmol/l or post-challenge glucose ≥11.1 mmol/l, confirmed within 12 weeks. The date of T2DM diagnosis was defined as the date of the first diagnostic value. New diagnoses were communicated to the participant’s primary care physician with his/her permission. An independent committee adjudicated the small number of cases where patients received a diagnosis or were started on glucose-lowering medication without undergoing study-specified laboratory investigations.
Statistical Analysis Physical activity was quantified as the mean daily step count over 7 days. Values of zero were classified as missing data. To explore any potential change in step count after T2DM diagnosis, we fitted general linear models for longitudinal pedometer steps allowing for correlation between repeated activity levels within subjects. Diagnosis was captured with a binary indicator value of ‘0’ for time points before diagnosis and ‘1’ afterwards. We used the Akaike information criterion to compare alternative correlation structures for repeated within-subject measures. An unstructured covariance had the best fit and was used; however, results are based on empirical standard errors which are robust to misspecification of the covariance structure. We first fitted a simple model (Model 1) where the only predictor was the binary indicator for diabetes. This model did not account for the possibility of a background trend in pedometer-measured activity. In Model 2, we adjusted for a linear trend over time to capture a potential shift in activity, beyond the background trend at diagnosis. Subgroup analyses were performed by age (
Diabetes, Obesity and Metabolism 16: 1265–1268, 2014. © 2014 John Wiley & Sons Ltd
Increased physical activity is known to be beneficial in people with type 2 diabetes mellitus (T2DM), but it is not known whether individuals change their activity levels after T2DM diagnosis. The present Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial, conducted in participants with impaired glucose tolerance at high cardiovascular risk, assessed ambulatory activity annually using research-grade pedometers. Oral glucose tolerance tests were performed annually and repeated to confirm T2DM diagnosis. This observational analysis used general linear models to compare step counts before and after T2DM diagnosis in the 2816 participants with the requisite data. Participants were relatively inactive at baseline, taking a median (interquartile range) of 5488 (3258–8361) steps/day, which decreased after T2DM diagnosis by a mean (s.e.) of 258 (64) steps/day (p < 0.0001); however, after adjusting for background trend for activity, step count after T2DM diagnosis was unchanged [mean (s.e.) of 103 (87) fewer steps/day; p = 0.23]. Awareness of T2DM diagnosis had no impact on the trajectory of activity established before the diagnosis. Keyword: observational study Date submitted 19 December 2013; date of first decision 20 February 2014; date of final acceptance 20 May 2014
Introduction Increased physical activity as part of general lifestyle improvement reduces the risk of development of type 2 diabetes mellitus (T2DM) [1,2] and improves cardiovascular risk factors, although a reduction in cardiovascular events has not been shown [3,4]. The American Diabetes Association and other bodies advise that those with T2DM or impaired glucose tolerance (IGT) increase activity levels to >150 min/week [5–7]. It is unknown whether individuals increase their activity levels after T2DM diagnosis. Improved physical activity after T2DM diagnosis would suggest that lifestyle advice is being given and acted upon, or that patients are taking their own initiative, whereas absence of improvement would suggest that barriers exist to the uptake or provision of lifestyle advice. To date, no studies have examined the impact of T2DM diagnosis on activity. We investigated whether physical activity levels, measured by pedometer steps, change after T2DM diagnosis in the present Nateglinide and Valsartan in Impaired Glucose Tolerance Outcomes Research (NAVIGATOR) trial.
Materials and Methods Study Population The present NAVIGATOR trial (NCT00097786) was a multinational randomized, placebo-controlled, 2 × 2 factorial trial investigating the respective effects of Nateglinide and Valsartan on cardiovascular risk and new-onset diabetes in participants with IGT [8] and existing cardiovascular disease or high Correspondence to : Dr David Preiss, BHF Glasgow Cardiovascular Research Centre, University of Glasgow, 126 University Place, Glasgow G12 8TA, UK. E-mail: [email protected]
cardiovascular risk [9,10]. Patients were enrolled between January 2002 and January 2004, and followed up for 5 years, for progression to T2DM (n = 9306). To evaluate pedometer activity before and after T2DM diagnosis, we included only patients who progressed to T2DM and who contributed pedometer data at least once before and once after T2DM diagnosis (n = 2816). All participants provided written consent. Ethical approval was obtained for the study for all sites.
Lifestyle Advice All participants took part in a standard lifestyle modification programme. One element consisted of advice to increase activity to >150 min/week. Study personnel administered the programme to all participants, who received relevant reading materials at visits within the first year (0.5, 1, 3, 6 and 12 months), with additional reinforcement through telephone contacts thereafter.
Physical Activity Habitual ambulatory activity was assessed using research-grade pedometers (Accusplit, San Jose, CA, USA). Two weeks after the baseline measurements, and annually thereafter, participants received pedometers and were instructed to wear them during waking hours for 7 consecutive days. Participants were instructed to record their daily step count in a log book and return it to the study team.
Diagnosis of T2DM During the Study Biochemical measures, including an oral glucose tolerance test, were repeated annually. Fasting plasma glucose (FPG) level was measured every 6 months for the first 3 years,
RESEARCH LETTER
Change in levels of physical activity after diagnosis of type 2 diabetes: an observational analysis from the NAVIGATOR study
research letter then annually. T2DM was defined as FPG ≥7.0 mmol/l or post-challenge glucose ≥11.1 mmol/l, confirmed within 12 weeks. The date of T2DM diagnosis was defined as the date of the first diagnostic value. New diagnoses were communicated to the participant’s primary care physician with his/her permission. An independent committee adjudicated the small number of cases where patients received a diagnosis or were started on glucose-lowering medication without undergoing study-specified laboratory investigations.
Statistical Analysis Physical activity was quantified as the mean daily step count over 7 days. Values of zero were classified as missing data. To explore any potential change in step count after T2DM diagnosis, we fitted general linear models for longitudinal pedometer steps allowing for correlation between repeated activity levels within subjects. Diagnosis was captured with a binary indicator value of ‘0’ for time points before diagnosis and ‘1’ afterwards. We used the Akaike information criterion to compare alternative correlation structures for repeated within-subject measures. An unstructured covariance had the best fit and was used; however, results are based on empirical standard errors which are robust to misspecification of the covariance structure. We first fitted a simple model (Model 1) where the only predictor was the binary indicator for diabetes. This model did not account for the possibility of a background trend in pedometer-measured activity. In Model 2, we adjusted for a linear trend over time to capture a potential shift in activity, beyond the background trend at diagnosis. Subgroup analyses were performed by age (
