Timing of physical activity in relation to liver fat content and insulin resistance

Abstract

Aims/hypothesis: We hypothesised that the insulin-sensitising effect of physical activity depends on the timing of the activity. Here, we examined cross-sectional associations of breaks in sedentary time and timing of physical activity with liver fat content and insulin resistance in a Dutch cohort.

Methods: In 775 participants of the Netherlands Epidemiology of Obesity (NEO) study, we assessed sedentary time, breaks in sedentary time and different intensities of physical activity using activity sensors, and liver fat content by magnetic resonance spectroscopy (n=256). Participants were categorised as being most active in the morning (06:00-12:00 hours), afternoon (12:00-18:00 hours) or evening (18:00-00:00 hours) or as engaging in moderate-to-vigorous-physical activity (MVPA) evenly distributed throughout the day. Most active in a certain time block was defined as spending the majority (%) of total daily MVPA in that block. We examined associations between sedentary time, breaks and timing of MVPA with liver fat content and HOMA-IR using linear regression analyses, adjusted for demographic and lifestyle factors including total body fat. Associations of timing of MVPA were additionally adjusted for total MVPA.

Results: The participants (42% men) had a mean (SD) age of 56 (4) years and a mean (SD) BMI of 26.2 (4.1) kg/m². Total sedentary time was not associated with liver fat content or insulin resistance, whereas the amount of breaks in sedentary time was associated with higher liver fat content. Total MVPA (-5%/h [95% CI -10%/h, 0%/h]) and timing of MVPA were associated with reduced insulin resistance but not with liver fat content. Compared with participants who had an even distribution of MVPA throughout the day, insulin resistance was similar (-3% [95% CI -25%, 16%]) in those most active in morning, whereas it was reduced in participants who were most active in the afternoon (-18% [95% CI -33%, -2%]) or evening (-25% [95% CI -49%, -4%]).

Conclusions/interpretation: The number of daily breaks in sedentary time was not associated with lower liver fat content or reduced insulin resistance. Moderate-to-vigorous activity in the afternoon or evening was associated with a reduction of up to 25% in insulin resistance. Further studies should assess whether timing of physical activity is also important for the occurrence of type 2 diabetes.

Keywords: Epidemiology; Insulin resistance; Liver fat; Physical activity; Sedentary behaviour; Sedentary breaks; Timing.

Fig. 1

Distribution of MVPA presented as mean percentage with 95% CIs per hour throughout the day for total population (a) and for the four subgroups based on timing of MVPA (b). Orange triangles, most MVPA in the morning (16% of population); green diamonds, most MVPA in the afternoon (63% of population); blue squares, most MVPA in the evening (8% of population); grey squares, even distribution of MVPA throughout the day (13% of population). Results are based on analyses weighted towards the BMI distribution of the general population (n=775; i.e. 13% represents around 100 participants)

Fig. 2

Relative changes in liver fat content (a) and insulin resistance (b) between subgroups based on timing of MVPA, compared with an even distribution of MVPA throughout the day. All associations were adjusted for age, sex, educational background, ethnicity, alcohol consumption, smoking, Dutch healthy diet index, total body fat and total MVPA. Results are based on analyses weighted towards the BMI distribution of the general population and were derived from regression coefficients with 95% CIs from linear regression analyses and expressed as a relative change. Such relative change can be interpreted as a ratio (e.g. 0.8 can be interpreted as 0.8-fold reduced liver fat content for most MVPA in the evening vs an even distribution of MVAP, which would reflect a decrease in liver fat content from, for example, 5% to 4%). Associations with insulin resistance were based on the total study population (n=775; i.e. 13% represents around 100 participants). Associations with liver fat content were based on participants with ¹H-MRS of liver fat (n=206; i.e. 15% represents around 31 participants). Percentages in brackets indicate proportion of the study population within the subgroups with most MVPA in the morning, afternoon or evening, or with an even distribution of MVPA throughout the day. Participants with alcohol consumption ≥40 g per day were excluded from the analyses of liver fat content