A University College London study has found that an additional 60 minutes of light activity (such as walking or doing chores) daily at age 12 was associated with a 10% reduction in depressive symptoms at age 18.
"Our findings show that young people who are inactive for large proportions of the day throughout adolescence face a greater risk of depression by age 18. We found that it's not just more intense forms of activity that are good for our mental health, but any degree of physical activity that can reduce the time we spend sitting down is likely to be beneficial," said the study's lead author, PhD student Aaron Kandola (UCL Psychiatry). "We should be encouraging people of all ages to move more, and to sit less, as it's good for both our physical and mental health."
The research team used data from 4,257 adolescents, who have been participating in longitudinal research from birth as part of the University of Bristol Children of the 90s cohort study. The children wore accelerometers to track their movement for at least 10 hours over at least three days, at ages 12, 14 and 16.
The accelerometers reported whether the child was engaging in light activity (which could include walking or hobbies such as playing an instrument or painting), engaging in moderate-to-physical activity (such as running or cycling), or if they were sedentary. The use of accelerometers provided more reliable data than previous studies which have relied on people self-reporting their activity, which have yielded inconsistent results.
Depressive symptoms, such as low mood, loss of pleasure and poor concentration, were measured with a clinical questionnaire. The questionnaire measures depressive symptoms and their severity on a spectrum, rather than providing a clinical diagnosis.
Between the ages of 12 and 16, total physical activity declined across the cohort, which was mainly due to a decrease in light activity (from an average of five hours, 26 minutes to four hours, five minutes) and an increase in sedentary behaviour (from an average of seven hours and 10 minutes to eight hours and 43 minutes).
The researchers found that every additional 60 minutes of sedentary behaviour per day at age 12, 14 and 16 was associated with an increase in depression score of 11.1%, 8% or 10.5%, respectively, by age 18. Those with consistently high amounts of time spent sedentary at all three ages had 28.2% higher depression scores by age 18.
Every additional hour of light physical activity per day at age 12, 14 and 16 was associated with depression scores at age 18 that were 9.6%, 7.8% and 11.1% lower, respectively.
The researchers found some associations between moderate-to-vigorous activity at earlier ages and reduced depressive symptoms, although they caution that their data was weaker due to low levels of activity of such intensity in the cohort (averaging around 20 minutes per day), so the findings do not clarify whether moderate-to-vigorous activity is any less beneficial than light activity.
While the researchers cannot confirm that the activity levels caused changes to depressive symptoms, the researchers accounted for potentially confounding factors such as socioeconomic status, parental history of mental health, and length of time wearing the accelerometer, and avoided the possibility of reverse causation by adjusting their analysis to account for people with depressive symptoms at the study outset.
"Worryingly, the amount of time that young people spend inactive has been steadily rising for years, but there has been a surprising lack of high-quality research into how this could affect mental health. The number of young people with depression also appears to be growing and our study suggests that these two trends may be linked," Kandola added.
The study's senior author, Dr Joseph Hayes (UCL Psychiatry and Camden and Islington NHS Foundation Trust), said: "A lot of initiatives promote exercise in young people, but our findings suggest that light activity should be given more attention as well."
"Light activity could be particularly useful because it doesn't require much effort and it's easy to fit into the daily routines of most young people. Schools could integrate light activity into their pupils' days, such as with standing or active lessons. Small changes to our environments could make it easier for all of us to be a little bit less sedentary," he added.
Background: Identifying modifiable risk factors is essential to reduce the prevalence adolescent depression. Self-report data suggest that physical activity and sedentary behaviour might be associated with depressive symptoms in adolescents. We examined associations between depressive symptoms and objectively measured physical activity and sedentary behaviour in adolescents.
Methods: From a population-based cohort of adolescents whose mothers were invited to participate in the Avon Longitudinal Study of Parents and Children (ALSPAC) study, we included participants with at least one accelerometer recording and a Clinical Interview Schedule-Revised (CIS-R) depression score at age 17·8 years (reported as age 18 years hereafter). Amounts of time spent in sedentary behaviour and physical activity (light or moderate-to-vigorous) were measured with accelerometers at around 12 years, 14 years, and 16 years of age. Total physical activity was also recorded as count per minute (CPM), with raw accelerometer counts averaged over 60 s epochs. Associations between the physical activity and sedentary behaviour variables and depression (CIS-R) scores at age 18 years were analysed with regression and group-based trajectory modelling.
Findings: 4257 adolescents from the 14 901 enrolled in the ALSPAC study had a CIS-R depression score at age 18 years. Longitudinal analyses included 2486 participants at age 12 years, 1938 at age 14 years, and 1220 at age 16 years. Total follow-up time was 6 years. Total physical activity decreased between 12 years and 16 years of age, driven by decreasing durations of light activity (mean 325·66 min/day [SD 58·09] at 12 years; 244·94 min/day [55·08] at 16 years) and increasing sedentary behaviour (430·99 min/day [65·80]; 523·02 min/day [65·25]). Higher depression scores at 18 years were associated with a 60 min/day increase in sedentary behaviour at 12 years (incidence rate ratio [IRR] 1·111 [95% CI 1·051–1·176]), 14 years (1·080 [1·012–1·152]), and 16 years of age (1·107 [1·015–1·208]). Depression scores at 18 years were lower for every additional 60 min/day of light activity at 12 years (0·904 [0·850–0·961]), 14 years (0·922 [0·857–0·992]), and 16 years of age (0·889 [0·809–0·974]). Group-based trajectory modelling across 12–16 years of age identified three latent subgroups of sedentary behaviour and activity levels. Depression scores were higher in those with persistently high (IRR 1·282 [95% CI 1·061–1·548]) and persistently average (1·249 [1·078–1·446]) sedentary behaviour compared with those with persistently low sedentary behaviour, and were lower in those with persistently high levels of light activity (0·804 [0·652–0·990]) compared with those with persistently low levels of light activity. Moderate-to-vigorous physical activity (per 15 min/day increase) at age 12 years (0·910 [0·857–0·966]) and total physical activity (per 100 CPM increase) at ages 12 years (0·941 [0·910–0·972]) and 14 years (0·965 [0·932–0·999]), were negatively associated with depressive symptoms.
Interpretation: Sedentary behaviour displaces light activity throughout adolescence, and is associated with a greater risk of depressive symptoms at 18 years of age. Increasing light activity and decreasing sedentary behaviour during adolescence could be an important target for public health interventions aimed at reducing the prevalence of depression.
Aaron Kandola, Gemma Lewis, David P J Osborn, Brendon Stubbs, Joseph F Hayes