Lowering physical activity impairs glycemic control in healthy volunteers

Abstract

Introduction: Postprandial glucose (PPG) is an independent predictor of cardiovascular events and death, regardless of diabetes status. Whereas changes in physical activity produce changes in insulin sensitivity, it is not clear whether changes in daily physical activity directly affect PPG in healthy free-living persons.

Methods: We used continuous glucose monitors to measure PPG and PPG excursions (ΔPPG, postmeal - premeal blood glucose) at 30-min increments after meals in healthy habitually active volunteers (n = 12, age = 29 ± 1 yr, body mass index = 23.6 ± 0.9 kg·m(-2), VO2max = 53.6 ± 3.0 mL·kg(-1)·min(-1)) during 3 d of habitual (≥10,000 steps per day) and reduced (<5000 steps per day) physical activity. Diets were standardized across monitoring periods, and fasting-state oral glucose tolerance tests (OGTT) were performed on the fourth day of each monitoring period.

Results: During 3 d of reduced physical activity (12,956 ± 769 to 4319 ± 256 steps per day), PPG increased at 30 and 60 min after a meal (6.31 ± 0.19 to 6.68 ± 0.23 mmol·L(-1) and 5.75 ± 0.16 to 6.26 ± 0.28 mmol·L(-1), P < 0.05 relative to corresponding active time point), and ΔPPG increased by 42%, 97%, and 33% at 30, 60, and 90 min after a meal, respectively (P < 0.05). Insulin and C-peptide responses to the OGTT increased after 3 d of reduced activity (P < 0.05), and the glucose response to the OGTT did not change significantly.

Conclusions: Thus, despite evidence of compensatory increases in plasma insulin during an OGTT, ΔPPG assessed by continuous glucose monitoring systems increased markedly during 3 d of reduced physical activity in otherwise healthy free-living individuals. These data indicate that daily physical activity is an important mediator of glycemic control, even among healthy individuals, and reinforce the utility of physical activity in preventing pathologies associated with elevated PPG.

Figures

FIGURE 1. Study Design

Postprandial glucose responses were measured via continuous glucose monitoring systems (CGMS) during three days of habitual (≥10,000 step/d; ACTIVE phase) or reduced (

FIGURE 2. (A) Daily pedometer steps

Number of steps taken each day by healthy volunteers (n=12) during three days of habitual (ACTIVE) or reduced physical activity (INACTIVE). □ Mean±SEM steps per day during the ACTIVE phase; Δ Mean±SEM steps per day taken during the INACTIVE phase. (B, C) Postprandial glucose (PPG) and glucose excursions (ΔPPG). Three days of reduced physical activity resulted in significant increases in (A) PPG and (B) ΔPPG. PPGpeak was also significantly elevated. All data are expressed as means±SEM. *Significantly different from ACTIVE (P < 0.05).

FIGURE 3. Glucose Tolerance

Glucose (A, B), insulin (C,D), and C-peptide (E,F) responses to a 75 g oral glucose tolerance test in physically active, healthy volunteers before (ACTIVE) and after three days of reduced physical activity (INACTIVE). AUC – area under the curve. All data are expressed as means±SEM. *Significantly different from baseline (P