By Matthew Warren

It’s well known that teenagers’ moods go through drastic changes. In particular, depressive symptoms – like feelings of low mood or self-loathing – tend to increase as they grow older. Now researchers have plotted out the exact trajectory of these depressive symptoms. In their recent paper in Journal of Youth and Adolescence, Alex Kwong and colleagues from the University of Bristol report for the first time the points during teen development when symptoms increase most rapidly, on average – and they find that these timings differ between young men and women.

The timing of symptom increases is of more than theoretical interest. Having more serious depression symptoms in adolescence is a known risk factor for developing depression later on in life, suggesting it could be useful to intervene and treat symptoms when they are at their worst. But when is that exactly? Past research has shown that, on average, depressive symptoms peak at some point in mid-to-late adolescence before decreasing again, but findings have been inconsistent: Scientists have suggested that peak depressive symptoms could occur as early as age 15 or as late as 20. And few studies have pinpointed other potentially important periods, such as the point at which depressive symptoms are increasing most rapidly, rather than simply when they have reached a peak.

To better characterise these critical points, Kwong’s team examined data from the Avon Longitudinal Study of Parents and Children. This study has been following children from birth in the 1990s through to today, providing an overview of development from childhood all the way through to adulthood.

The team looked at participants’ scores on the short mood and feelings questionnaire from the ages of 10 to 22. This questionnaire measures depressive symptoms over the previous two weeks, asking participants to indicate whether statements like “I felt miserable or unhappy” are true for them. Over the 12 year time period, participants had been given the questionnaire on eight separate occasions (although not everyone had completed every questionnaire: 7,335 participants completed the first questionnaire, decreasing to 3,850 by the final one).

The researchers fit a model to this data, showing the path of depressive symptoms for each individual through adolescence and early adulthood. They then averaged these curves across males and females, to give the general trajectory for each sex.

The team found that there were key differences between male and female participants. Females had higher depressive symptoms in general throughout their adolescence, except for between ages 10 and 11, when symptoms were higher for males. The symptoms didn’t peak until around age 20 for both sexes, but there were sex differences in the age at which symptoms increased most rapidly: for females this occurred at 13.7 years old, while for males it was much later, at 16.4 years old.

The researchers say that these sex differences in the trajectories could relate partly to puberty. Girls generally go through puberty earlier, which could explain why their depressive symptoms increase most rapidly almost 3 years earlier than boys’ symptoms. This also suggests that girls could benefit earlier than boys from interventions designed to prevent the increase of depressive symptoms.

However, this study is the first to estimate the age at which depressive symptoms increase most rapidly, so the findings should be considered preliminary. It’s also not yet clear whether it’s possible to slow or reverse these rapid increases in teen depression symptoms – or what the later effects of doing so would be. Nevertheless, the authors say, “if this can be used for clinical purposes, it may be possible to treat individuals at this age, which may help reduce depressive symptoms or depression at a later stage.”

—Identifying Critical Points of Trajectories of Depressive Symptoms from Childhood to Young Adulthood

Matthew Warren (@MattbWarren) is Staff Writer at BPS Research Digest