Interrupting sitting time as a means to improve glucose metabolism in T2DM
Breaking sitting with light activities vs structured exercise: a randomised crossover study demonstrating benefits for glycaemic control and insulin sensitivity in type 2 diabetes.
Moderate- to vigorous-intensity exercise is important in the prevention and treatment of type 2 diabetes (T2DM) [1,2], but over 90% of healthy adults do not adhere to the recommendation of current guidelines to do at least 150 min/week of exercise . Non-compliance may be even higher in those with T2DM-related comorbidities such as muscle weakness and peripheral neuropathy, which can be a barrier to physical activity. Alternatives to exercise are therefore needed.
Results of recent observational studies suggest an association between sedentary time and risk of T2DM, independent of the time spent exercising [4,5]. Experimental studies in laboratory conditions suggest that regular interruption of sitting with small bouts of walking may lower glucose and insulin levels in healthy and overweight/obese adults and in those with T2DM [6-10]. In free-living conditions, it has been shown that replacing sitting time with standing and light-intensity walking was more efficient at improving insulin action than replacement with one bout of moderate- to vigorous-intensity exercise in healthy sedentary participants .
This study investigated whether these findings could be replicated in those with T2DM, by breaking up sitting time with standing and light-intensity walking and comparing it with structured exercise, under conditions of comparable energy expenditure. Adults with T2DM who exercised less than 2.5 hours/week were instructed to discontinue lipid-lowering drugs and cholesterol-lowering margarines 14 days prior to starting the first regimen.
In a cross-over design, participants followed three activity regimes ‘sitting’ (max 1 hour walking and 1 hour standing per day), ‘exercise’ (1 hour supervised cycling per day) and ‘sit less’ (5 h/day sitting replaced with 2 h walking and 3 h standing, and breaking up sitting time, preferably every 30 min), each for 4 days in free-living conditions. Adherence to the regimens was monitored with an advanced accelerometer. A wash-out period between the successive activity regimes was applied. The order of the intervention was randomised. It was calculated that 19 participants were needed to detect a mean difference of 1.7 mmol/l in 24 h glucose between the activity regimens, with a power of 80%.
- Substitution of time spent sitting by ambulatory time reduced 24h glucose levels in the Sit Less regimen as compared with Sitting (mean [SEM]: 7.35 [0.19] vs. 7.69 [0.23] mmol/L, P=0.014). No significant difference was seen between the Sit Less and Exercise regimens (Exercise: 7.29 [0.24} mmol/L, P=0.741).
- iAUC provides a summary measure of the increase above fasting glucose level during the subsequent 24 h observation period. iAUC reduced significantly from 1974  min*mmol/L in the Sitting regimen to1263  min*mmol/L in the Sit Less regimen (P=0.002). Structured exercise reduced 24h glucose excursion to 1383  min*mmol/L), but this did not significantly differ from the Sitting regimen (p=0.069).
- Duration of hyperglycaemia over a 24 h time span was almost halved, from 211  min/day in the Sitting regimen, to 118  min/day in the Sit Less regimen (p=0.002). The Exercise regimen showed intermediate results with 152  min/day.
- Fasting insulin levels did not differ between the Exercise (102  pmol/L) and Sitting regimen ((108  pmol/L, p=0.117), but Sit Less showed significantly lower ((95  pmol/L) levels than Sitting. Likewise, Sit Less resulted in lower HOMA2-IR values than Sitting (1.89 [0.26] vs. 2.16 [0.26], P=0.001), and vs. Exercise (2.06 [0.28], P=0.015).
- An 0.5 MET x h/day difference was estimated between Exercise and Sit Less regimens. Energy intake did not differ significantly between the three regimens.
These data show that the Sit Less regimen improved insulin sensitivity, mean 24 h glucose levels, 24h glucose excursions, duration of hyperglycaemia and fasting triacylglycerol levels. In this study, the general effect of the Sit Less regimen on glucose homeostasis tended to be a little more potent than the effect of structured exercise. Insulin sensitivity was more improved after the Sit Less regimen than after the Exercise regimen. In this respect is it interesting to note that during the Exercise regimen participants spent most of the day sitting. It is thus proposed that the duration of non-sitting activities may be more important than the intensity of these activities.
The volume of light-intensity activities in this study was relatively high as compared with what is generally observed in T2DM patients, thus future studies may establish what activity regimen might be more feasible.