displays the descriptive characteristics of participants at baseline and follow-up. The mean follow-up time was 405 ± 103 days. Men were heavier and taller and had a higher FFM than women (P < 0.001). Fasting glucose (P < 0.01), insulin (P < 0.001), and the HOMA-IR score (P < 0.001) were also significantly higher in men than in women, whereas fat mass was higher in women (P < 0.001). Forty-nine percent of men and 36% of women were overweight, and, in addition, 27% of both men and women were obese.
Descriptive characteristics of participants at baseline and follow-up
Men spent more time sedentary (P < 0.01), whereas women spent more time at light-intensity activity (P < 0.05). In contrast, men reported significantly lower levels of TV viewing (P < 0.001). Self-reported TV viewing decreased significantly between baseline and follow-up (P < 0.05), whereas all other variables remained unchanged. We did not observe any significant sex by time interactions. Therefore, all subsequent analyses were performed with men and women combined, adjusted for sex.
Time spent sedentary was significantly and inversely associated with time spent at light-intensity activity at baseline and follow-up (r = −0.52, P < 0.0001; r = −0.48, P < 0.0001) and time spent at light-intensity activity was significantly and positively correlated with time spent at MVPA at follow-up (r = 0.24, P = 0.009) but not at baseline. Self-reported TV viewing was significantly and inversely associated with time spent at light-intensity activity at baseline and follow-up (r = −0.16, P = 0.027; r = −0.24, P = 0.001) but was not associated with any of the other objectively measured time estimates. Self-reported TV viewing at baseline was significantly correlated with TV viewing at follow-up (r = 0.78, P < 0.001). Similarly, all objectively measured time estimates at baseline were significantly correlated with their corresponding time estimates at follow-up (r = 0.61 to 0.63, P < 0.0001), indicating a high degree of stability of patterns of physical activity.
shows the cross-sectional and prospective associations between time estimates of physical activity and self-reported TV viewing with insulin resistance. In cross-sectional analyses, time (minutes per day) spent at MVPA was significantly and inversely associated with HOMA (β = −0.004 [95% CI −0.008 to −0.00001], P = 0.048) and fasting insulin (β = −0.005 [−0.008 to −0.001], P = 0.017), independent of time spent sedentary, time spent at light-intensity activity, sex, age, smokingstatus, waist circumference, and self-reported TV viewing. TV viewing was significantly and positively associated with HOMA (β = 0.01 [95% CI 0.004–0.019], P = 0.002) and fasting insulin (β = 0.01 [0.004–0.017], P = 0.002), independent of objectively measured time estimates and the same confounders as above.
Associations between objectively measured time estimates of physical activity and self-reported TV and video viewing at baseline with the HOMA score and fasting insulin in adults with a family history of type 2 diabetes
We thereafter examined whether time spent sedentary, at light-intensity activity and at MVPA, and TV viewing predicted insulin resistance at follow-up. Time spent at MVPA was a significant predictor of fasting insulin (β = −0.004 [95% CI −0.007 to −0.0001], P = 0.022), and the association approached significance for HOMA (β = −0.003 [−0.007 to 0.000002], P = 0.052), independent of baseline phenotype, follow-up time, and other confounding factors. Similar to results for the cross-sectional analyses, time spent sedentary and at light-intensity activity were not significantly associated with insulin resistance at follow-up. In contrast to the cross-sectional analyses, TV viewing did not predict insulin resistance at follow-up (β = −0.0006 [−0.007 to 0.006], P = 0.84, and β = 0.00007 [−0.006 to −0.006], P = 0.94, for HOMA and fasting insulin, respectively).
Then we examined whether the change in MVPA and TV viewing between baseline and follow-up was associated with insulin resistance. The change in MVPA was significantly and inversely related to the change in fasting insulin (β = −0.003 [95% CI −0.007 to −0.0003], P = 0.032) and the HOMA score (β = −0.004 [−0.008 to −0.001], P = 0.015) after adjustment for sex, baseline phenotype, age, waist, smoking status, TV viewing, and follow-up time. In contrast, the change in TV viewing was not associated with either fasting insulin (β = 0.003 [−0.006 to 0.011], P = 0.55) or the HOMA score (β = 0.004 [−0.005 to 0.013], P = 0.42).
Finally, we analyzed whether meeting the recommendations of accumulating 30 min/day of MVPA at baseline was associated with fasting insulin at follow-up. Meeting this activity guideline was associated with a significantly lower mean value for fasting insulin (geometric mean difference between groups 1.12 pmol/l [95% CI 1.02–1.24], P = 0.002), independent of baseline insulin levels and the same confounders as above. shows fasting insulin levels at follow-up, stratified according to baseline BMI group (normal, overweight, or obese) and the dichotomous variable of meeting/not meeting the physical activity guidelines at baseline. BMI group (Ptrend = 0.004) and meeting activity guidelines (Ptrend = 0.050) predicted fasting insulin at follow-up, independent of each other and of baseline fasting insulin, age, sex, smoking status, TV viewing, and follow-up time.
Figure 1 Fasting insulin (geometric mean) at follow-up stratified by BMI group (normal weight, overweight, and obese) and according to achieving at least 30 min of MVPA per day (yes vs. no). Data are adjusted for sex, baseline age, baseline fasting insulin, baseline (more ...)