OBJECTIVELY MEASURED LIGHT-INTENSITY PHYSICAL ACTIVITY IS INDEPENDENTLY ASSOCIATED WITH 2-H PLASMA GLUCOSE
Healy GN, Dunstan DW, Salmon J, et al
Diabetes Care. 2007;30(6):1384-1389; E-pub 2007.
Objective
We examined the associations of objectively measured sedentary time, light-intensity physical activity, and moderate- to vigorous-intensity activity with fasting and 2-hour postchallenge plasma glucose in Australian adults.
Research Design and Methods
A total of 67 men and 106 women (mean age = 53.3 +/- 11.9 years) without diagnosed diabetes were recruited from the 2004-2005 Australian Diabetes, Obesity, and Lifestyle study. Physical activity was measured by Actigraph accelerometers worn during waking hours for 7 consecutive days and summarized as sedentary time (<100 accelerometer counts/min; average hours per day), light-intensity activity (100-1,951 counts/min), and moderate- to vigorous-intensity activity (>1,952 counts/min). An oral glucose tolerance test was used to ascertain 2-hour plasma glucose (2-h PG) and fasting plasma glucose (FPG) levels.
Results
After adjustment for confounders (including waist circumference), sedentary time was positively associated with 2-h PG (b = 0.29, 95% confidence interval [CI] = 0.11-0.48, P = .002) and light-intensity activity time (b = -0.25, -0.45 to -0.06, P = .012) and moderate- to vigorous-intensity activity time (b = -1.07, -1.77 to -0.37, P = .003) were negatively associated with 2-h PG. Light-intensity activity remained significantly associated with 2-h PG following further adjustment to moderate- to vigorous-intensity activity (b = -0.22, -0.42 to -0.03, P = .023). Associations of all activity measures with FPG were nonsignificant (P > .05).
Conclusions
These data provide the first objective evidence that light-intensity physical activity is beneficially associated with blood glucose level and that sedentary time is unfavorably associated with blood glucose level. These objective data support previous findings from studies using self-report measures, and suggest that substituting light-intensity activity for television viewing or other sedentary time may be a practical and achievable preventive strategy to reduce the risk of type 2 diabetes and cardiovascular disease.
Editor's Comment. This study by Healy and colleagues is interesting on more than 1 level. First, few studies are currently available that address the role of light-intensity physical activity and its effects on risk factors or physiological variables. Most of the research on exercise/activity (other than epidemiological data) uses what is defined in this study as "moderate to vigorous" activity. This study was designed to assess 3 levels of sedentary- to vigorous-intensity activity and to study their relationship to both FPG and 2-h PG levels. Healy and her colleagues statistically controlled for confounders such as weight, waist circumference, etc. The data show that light activity, as well as moderate to vigorous activity, is related to lower 2-h PG. Light-intensity activity was also a significant predictor in 3 of the 4 regression models that were generated to predict 2-h PG. The other interesting factor is that these subjects did not have diabetes (type 1 or type 2). A recent meta-analysis (as well as other studies) has confirmed that elevated 2-h PG is related to both all-cause and cardiovascular mortality, even in the absence of diabetes. The other important outcome of this study is that even light-intensity activity is better than sedentary time. Intuitively, we all know this is true, even in people who engage in daily or regular exercise. We should be counseling patients and families to increase overall activity levels as well as to engage in regular exercise. Put in the reverse, being sedentary is unhealthy!!