Sedentary time determines adiposity in inactive individuals
Individuals with longer durations of sedentary time tend to have higher levels of inter- and intraorgan fat, thus emphasizing the importance of exercise, a recent study has shown.
“[T]he deleterious associations of objectively measured sedentary time with visceral, liver and total abdominal fat may be particularly pertinent for those individuals who do not undertake sufficient amounts of [moderate-to-vigorous physical activity (MVPA)]” said researchers.
“[T]he manner in which sedentary time is accumulated may influence the strength of the associations with markers of MRI-derived adiposity,” they added.
In 124 participants (mean age 64.0±7.1 years; 65.3 percent male), each 60-minute duration of sedentary time was significantly associated with greater liver fat (β, 1.86 percent; 95 percent CI, 1.14–2.52; p<0.001), visceral fat (β, 0.62 L; 0.32–0.92; p<0.001), subcutaneous fat (β, 1.14 L; 0.54–1.74; p<0.001) and total abdominal fat (β, 1.74 L; 0.96–2.46; p<0.001). [Obesity 2018;doi:10.1002/oby.22034]
None of the associations were attenuated after further adjustments for MVPA, but only liver fat (β, 1.44; 0.66–2.22; p<0.001) and visceral fat (β, 0.36; 0.06–0.60; p=0.013) remained significantly correlated with sedentary time after controlling for body mass index (BMI).
Bouts of prolonged sedentary time that lasted 30–60 minutes were also significantly associated with higher liver (β, 1.44 percent; 0.18–2.70), visceral (β, 0.78 L; 0.36–1.26), subcutaneous (β, 1.08 L; 0.12–2.04) and total abdominal fat (β, 1.86 L; 0.66–3.12). Only visceral fat remained statistically significant after adjustments for BMI (β, 0.48 L; 0.18–0.78).
The trend was similar for bouts of sedentary time exceeding 60 minutes, which were significantly correlated with higher total abdominal (β, 2.88 L; 1.62–4.08), visceral (β, 0.66 L; 0.24–1.08) and liver fat (β, 1.44 percent; 0.66–2.22).
Interestingly, a greater number of breaks in sedentary time correlated significantly with reductions in visceral (β, –0.06 L; –0.85 to –0.26), subcutaneous (β, –0.68 L; –1.35 to –0.01) and total abdominal fat (β, –0.12 L; –0.21 to –0.04). While adjustments for total sedentary time, BMI and MVPA attenuated the relationships, this finding suggested a protective effect of exercise.
Interaction analyses confirmed that exercise had a modifying effect on the association between fat and sedentary time. For instance, 60-minute bouts of sedentary time significantly increased liver (β, 2.16 percent; 1.08–3.30; p<0.001), visceral (β, 0.54 L; 0.12–0.96; p=0.014) and total abdominal fat (β, 1.80 L; 0.54–3.06; p=0.005) in inactive (n=66) but not in active (n=58) participants.
“To our knowledge, this study is the first to look at the modifying influence of MVPA on associations between sedentary time and MRI-derived fat distribution,” the researchers said, noting that physical activity appears to protect against the detrimental effects of sedentary time on adipose tissue buildup and cardiovascular risks.
“Taken together, the experimental and cross-sectional literature have implied that sedentary time may be not be as pertinent in individuals with a relatively high fitness level or in those who engage in recommended levels of MVPA.”