Sedentary time may enlarge adolescents' hearts

In adolescents, sedentary time may increase heart size three times more than moderate-to-vigorous physical activity. That’s according to a new study published in the Scandinavian Journal of Medicine & Science in Sports, conducted by the University of Bristol, the University of Exeter and the University of Eastern Finland.

Physical inactivity has been associated with several non-communicable diseases in adults, such as cardiovascular diseases, type 2 diabetes and cancer. In the paediatric population, the majority of movement behaviour studies have focused on the effect of sedentary behaviour and physical activity on cardiometabolic health, which includes blood pressure, insulin resistance, blood lipids and body mass index. But there has been a gap in knowledge on the effect of sedentary time and moderate-to-vigorous physical activity on cardiac structure and function in large adolescent populations, due to the scarcity of device-measured movement behaviour and echocardiography assessment in the paediatric population.

The new study, which used data from the University of Bristol study Children of the 90s (also known as the Avon Longitudinal Study of Parents and Children), included 530 adolescents aged 17 years. On average, these adolescents spent almost eight hours a day sedentary and about 49 minutes a day in moderate-to-vigorous physical activity. It was observed that both sedentary time and moderate-to-vigorous physical activity were associated with higher left ventricular mass, which indicates an enlarged or hypertrophied heart. A higher left ventricular mass and a reduced left ventricular function, which indicates decreased heart function, may in combination or independently lead to an increased risk of heart failure, myocardial infarction, stroke and premature cardiovascular death.

The increase in cardiac mass (3.8 g/m^2.7) associated with sedentary time was three times higher than the cardiac mass increase (1.2 g/m^2.7) associated with moderate-to-vigorous physical activity. This finding was observed in adolescents irrespective of their obesity status. Importantly, light physical activity was not associated with an increase in cardiac mass but was associated with better cardiac function estimated from left ventricular diastolic function.

“This novel evidence extends our knowledge of the adverse effects of sedentary time on cardiac health,” said Andrew Agbaje, a physician and clinical epidemiologist at the University of Eastern Finland.

“It is known among adults that a 5 g/m² increase in cardiac mass may increase the risk of cardiovascular disease and death by 7–20%. Engaging in moderate-to-vigorous physical activity also slightly enlarged the heart, but it seems an acceptable ‘negative side effect’ considering several other health benefits of moderate-to-vigorous exercise.

“Hence, public health experts, health policymakers, high school administrators and teachers, paediatricians, and caregivers are encouraged to facilitate adolescent participation in physical activity to enable a healthy heart.”

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