Physical activity associated with metabolic traits in adolescents
A recent study has found associations of physical activity with metabolic traits that are small in magnitude and stronger for higher moderate-to-vigorous physical activity (MVPA) vs sedentary time.
In addition, “[a]ctivity fluctuates over time, but associations of current activity with most metabolic traits did not differ by previous activity,” researchers said. “This suggests that the metabolic effects of physical activity, if causal, depend on most recent engagement.”
A total of 1,826 participants were recruited at birth in 1991–1992 via mothers participating in the Avon Longitudinal Study of Parents and Children offspring cohort who attended clinics in 2003–2005, 2005–2006 and 2006–2008 and were included in ≥1 analysis. Uniaxial accelerometers worn on the waist measured total activity (counts/min), MVPA (min/d) and sedentary time (min/d) over ≥3 d at mean ages of 12, 14 and 15 years.
Researchers also examined current activity (at age 15 years), mean activity across occasions, interaction by previous activity and change in activity relative to systolic and diastolic blood pressures, insulin, C-reactive protein, and 230 traits from targeted metabolomics (nuclear magnetic resonance spectroscopy), including lipoprotein cholesterol and triglycerides, amino and fatty acids, glycoprotein acetyls, and others.
There was a mean 477.5 counts/min of current total activity, while mean durations of MVPA and sedentary time were 23.6 and 522.1 min/d, respectively. At age 15 years, mean body mass index was 21.4 kg/m2. Low associations were seen between first and last activity measurement occasions (eg, r=0.40 for counts/min). [PLoS Med 2018;15:e1002649]
The strongest association of current activity was with cholesterol and triglycerides in high- (HDL) and very low-density lipoprotein (VLDL) particles (eg, –0.002 mmol/l or –0.18 SD units; 95 percent CI, –0.24 to 0.11 for triglycerides in chylomicrons and extremely large VLDL), and with glycoprotein acetyls (–0.02 mmol/l or –0.16 SD units; –0.22 to –0.10), among others. There were similar associations for mean activity across three occasions.
Modest attenuations were observed after adjustment for fat mass index based on dual-energy X-ray absorptiometry. Mutually adjusted models demonstrated opposite associations of higher MVPA and sedentary time with cholesterol and triglycerides in VLDL and HDL particles (MVPA more strongly related with glycoprotein acetyls and sedentary time with amino acids).
Based on longer-term measures, there appeared to be less consistent associations for sedentary time vs MVPA. Such relations were also weak for change in all activity types from age 12–15 years. In addition, there was weak evidence for interaction between activity types at age 15 years and previous activity measures relative to most traits (minimum p=0.003; median p=0.26 for counts/min), with interaction coefficients mostly positive.
“Physical activity is commonly thought to protect against cardiovascular disease, but direct causal evidence from randomized controlled trials and other studies designed to strengthen causal inference is sparse,” researchers said. [JAMA Cardiol 2016;1:568-574; BMJ 2016;354:i3857]
“Higher cholesterol content in LDL and remnant lipoproteins and higher total triglycerides are supported as causes of CHD [coronary heart disease] through Mendelian randomization studies and randomized controlled trials,” they added. [N Eng J Med 2015;372:2387-2397; N Engl J Med 2017;376:1713-1722; J Am Coll Cardiol 2015;65:1552-1561; Eur Heart J 2014;36:539-550]
The present study was limited by modest sample sizes and relatively short durations of accelerometry measurement on each occasion (3–7 d) and of time lengths between first and last accelerometry occasions (<4 years). Additionally, uniaxial accelerometers, which predated more sensitive triaxial devices, were used to record activity.