In adolescents, current physical activity level has a greater effect on metabolic health than time spent being sedentary, according to findings from a prospective cohort study published in PLOS Medicine.
“Much of what we know about device-measured physical activity for health is based on a snapshot of activity. To answer core questions about the nature of activity’s health effects — like whether they are long- or short-lived — requires repeated measures,” Joshua Bell, PhD, a research associate in the MRC Integrative Epidemiology Unit at the University of Bristol, United Kingdom, told Endocrine Today. “This is the first time multiple occasions of device-measured activity have been linked with these metabolic traits; these were based on novel metabolomics, which allowed a more comprehensive picture of metabolism than before.”
Bell and colleagues analyzed data from 1,826 children (55.6% girls) born between April 1991 and December 1992 to women participating in the Avon Longitudinal Study of Parents and Children. At age 12, 14 and 15 years, children wore an accelerometer between 3 and 7 days to measure bouts of moderate to vigorous physical activity and sedentary time, calculated as “counts per minute” with intense physical activity defined as any time above 3,600 counts per minute and sedentary time as readings at or below 199 counts per minute.
At age 15 years, participants underwent a physical exam to measure systolic and diastolic blood pressure, insulin and C-reactive protein; using proton nuclear magnetic resonance spectroscopy, researchers assessed 230 traits from targeted metabolomics, including lipoproteins, fatty acids, amino acids and inflammatory factors. Researchers used linear regression analysis to examine metabolic traits at age 15 years in relation to time spent in active and sedentary pursuits at age 15 years; in relation to the combination of active and sedentary time at age 12, 14 and 15 years; and in relation to changes in active and sedentary traits over time.
At age 15 years, mean total physical activity level was 477.5 counts per minute, mean time spent in moderate to vigorous activity was 23.6 minutes per day, and mean sedentary time was 522.1 minutes per day. From age 12, 14 and 15 years, total activity generally slowed while sedentary time increased. Moderate to vigorous activity remained at similar levels throughout the three data collection points, according to researchers.
Total activity at age 15 years was most strongly associated with VLDL particle concentrations and lipid fractions (P = 1.78 x 10-7). Increased activity was associated with lower total VLDL cholesterol (P = 5.13 x 10-5) and higher total HDL cholesterol (P = 3.8 x 10-5), but not with LDL, and with lower total triglyceride levels, but not in LDL particles. Associations were weaker between sedentary activity and metabolic traits at age 15 years, but the connections strengthened when encompassing measurement at all three ages.
“Patterns were strange for longer-term sedentary time, with more sitting linked beneficially with some traits, including lower remnant cholesterol,” Bell said. “This is unlikely to be real, but rather a sign that sitting time in adolescence is a marker for other important factors. For example, socioeconomic advantage can lead to more sitting while studying and also to better health, giving the illusion of sitting being beneficial. Links between time spent intensely active and metabolic traits were more robust.”
Although physical activity measured at age 15 years was associated with several metabolic traits, changes in activity of all three types (total, vigorous, sedentary) between age 12 and 15 years did not provide evidence for a strong connection.
“It’s never too late to benefit from physical activity, but we also need to remove barriers that make activity hard to keep up,” Bell said. “We can’t expect much benefit otherwise. Activity’s effects are good but short-lived, meaning we need to move often to prevent disease. Still, there’s a positive message: What matters is what you do right now.” – by Phil Neuffer
Disclosures: Bell reports that he was supported by a Cancer Research UK program grant. Please see the study for all other authors’ relevant financial disclosures.