Concussion and depressive symptoms in high school students: impact of physical activity and substance use

Abstract

Objective

To investigate the association between concussion history and depressive symptoms after adjusting for physical activity, substance use, and illicit drug use.

Methods

We analysed data from the Adolescent Behaviour and Experiences Survey, a nationally representative survey of adolescents in the USA. Our independent variables were history of concussion in the 12 months preceding survey completion; self-reported weekly physical activity (days per week with >60 min of physical activity, 0–7 scale); substance use over the past 30 days (yes vs no) and illicit drug use throughout lifetime (yes vs no). Our dependent variable was participant-reported sadness/hopelessness over the past 12 months (yes vs no).

Results

Among 7499 adolescents (9th–12th grade, 50.4% female), reporting one or more concussions over the past year was not associated with the odds of depressive symptoms (OR: 1.13, 95% CI: 0.93 to 1.37, p=0.21). Each additional day of physical activity per week was associated with a lower odds of depressive symptoms (OR: 0.91; 95% CI: 0.89 to 0.94; p<0.0001). Illicit drug use (OR ever vs never: 2.48; 95% CI: 1.96 to 3.13; p<0.0001) and substance use (OR yes vs no: 2.77; 95% CI: 2.34 to 3.29; p<0.001) were associated with a higher odds of depressive symptoms.

Conclusions

Adjusting for physical activity, substance use and illicit drug use, concussion was not significantly associated with depressive symptoms. This novel discovery informs clinicians as they counsel adolescents with concussion; future research should examine physical activity and avoidance of substance/illicit drug use as postinjury recommendations in an effort to lower the risk of depressive symptoms.

INTRODUCTION

Sport-related brain trauma has been proposed as a possible contributor to poor mental health among adolescent-aged individuals.^{1 2} Concussion, a mild form of traumatic brain injury, has been associated with disturbances in mental health symptoms^3-8 and is a common injury among adolescent athletes.^{9 10} Sports participation and recreational physical activity—where adolescents are at risk of sustaining concussion^{11 12}—have measurable benefits for mental health, physical health and social connectedness.^13-15 Though participation in some sports may present a higher risk of sustaining concussion,^{11 12} reducing or eliminating these sports for the sole purpose of injury mitigation is an ineffective strategy for supporting adolescent well-being. Instead, research and clinical practice would benefit from a better understanding the complex relationships between concussion and poor mental health outcomes, which may inform points of future clinical intervention before or after injury to reduce possible mental health sequelae.¹⁶

Physical inactivity and substance use are uniquely positioned as modifiable risk factors for postconcussion psychosocial sequelae, given their association with mental health outcomes among uninjured adolescents.^{14 15 17-20} Uninjured physically active adolescents are less depressed/anxious and have better overall mental health than their physically inactive counterparts.^{14 15 17 18} Among youth without recent injury, substance use, including drug or alcohol use, is associated with higher odds of mental health disorders.^{19 20} After a concussion has occurred, higher levels of physical activity early in recovery are associated with improved mental health outcomes.^21-25 Preliminary evidence suggests an association between sport-related concussions and increased risk of substance use in adolescent populations.^26-28 Yet, evidence remains sparse on the direct interplay between concussion, physical activity, substance use and mental health.

To address these critical evidence gaps, the primary purpose was to investigate the association of concussion and self-reported depressive symptoms in a nationally representative sample of US adolescents. Second, we aimed to test whether physical activity and/or substance use modified the association between concussion history and depressive symptoms. The results of this study will inform future clinical interventions for individuals with concussion to mitigate the risk of psychological sequelae. Our results will also identify the extent to which concussion contributes to poor mental health, after adjusting for important lifestyle factors with known connection to depressive symptoms.

METHODS

We analysed data from the Adolescent Behaviour and Experiences Survey (ABES), a nationally representative survey of health and behavioural-related outcomes among adolescents. The ABES is a stratified, three-stage cluster probability-based survey which enrolled adolescent-aged high school students in public and private schools across the USA. The survey contained >100 items assessing mental, physical and social domains of health, was administered between January and June 2021, and was completed by >7700 participants. A complete description of the ABES study design can be found in the ABES methodology paper.²⁹ The original purpose of the ABES was to evaluate the mental health of US high school students during the COVID-19 pandemic. The ABES dataset, SAS programs for statistical analyses and user manuals are open-access and were retrieved by the study team in August 2023 (https://www.cdc.gov/healthyyouth/data/abes.htm). Participants were not involved in the development of the survey. We used the ABES as secondary research data; the original sample size was determined by the study investigators (initiated by the Centers for Disease Control and Prevention (CDC)) and was sufficient to address the primary aim of their research. For our secondary analysis, the sample size of over 7000 adolescents is sufficient to examine associations between physical activity, substance use, concussion and depressive symptoms. We used all available data in the current study. ²⁹

Equity, diversity and inclusion

Participant data were weighted based on age, biological sex, race and ethnicity to account for non-response or undersampling of marginalised groups, as is the conventional approach for analysing data from the ABES.²⁹ ABES used a complex survey design to obtain nationally representative data. Typical survey weightings, including poststratification and non-response adjustments, were performed to account for school and student non-response, and correct for the oversampling of non-Hispanic black and Hispanic students. As a result, the demographics in the weighted sample match national student demographic distributions of sex and grade. The ABES survey design is described in greater detail by Rico et al.²⁹ The school response rate was 38%, the student response rate was 48%, according to the ABES report.²⁹

Outcome variable

Our primary measure of adolescent mental health was question #25 (Q25) in the ABES, which asked participants, ‘During the past 12 months, did you ever feel so sad or hopeless almost every day for two weeks or more in a row that you stopped doing some usual activities?’. The response option was a Yes/No selection. Several mental health-related questions are available for analysis in the ABES dataset; we selected Q25/hopelessness due to its use in past research as a proxy for depressive symptoms,⁷ and its association with suicidality in a 10-year longitudinal study.³⁰ In addition, the study’s aim was to investigate subclinical manifestations of depressive symptoms (ie, feelings of sadness/hopelessness vs clinically diagnosable depression).

Explanatory variables

Our primary explanatory variable was question #81 (Q81) in the ABES, which asked participants, ‘During the past 12 months, how many times did you have a concussion from playing a sport or being physically active?’ Given the rare occurrence of multiple concussions in the dataset (<5%), concussion history was modelled as a dichotomous variable: one or more concussions versus no concussion during the previous year. The literature regarding the cumulative effects of concussions on adolescent mental health is mixed; research has identified that sustaining more than one concussion is associated with increased psychological distress compared with sustaining one or no concussions,^{8 31} while others have found no significant difference in mental health outcomes among those sustaining one versus multiple concussions.³² Given that the primary purpose of this investigation is to investigate the impact of concussion history on depressive symptoms within the context of other lifestyle factors (ie, covariates), and due to the low occurrence of multiple concussions in the dataset, we dichotomised this variable.

Aligned with our secondary purpose, additional explanatory variables assessing physical activity and substance use were included in our analysis. Participation in physical activity was based on question #77 (Q77), ‘During the past 7 days, on how many days were you physically active for a total of at least 60 minutes per day?’ Response options ranged from 0 days to 7 days. For purposes of describing sample demographics, we dichotomised physical activity as physically active (>3 days of physical activity per week) or physically inactive (<3 days per week). However, physical activity was modelled in its true ordinal form in all subsequent analyses. Other measures of exercise or physical activity in the ABES survey included frequency of strength training (Q99) and the number of sports played (Q80). However, as these questions do not assess broad physical activity behaviours, they were not used in this investigation but could be important targets for future work.

For substance use, the ABES asked participants, ‘During the past 30 days, on how many days did you use…?’, with individual questions for cigarette smoking (Q32), electronic vape products (Q35), smokeless tobacco (Q37), cigars/cigarillos (Q38), at least one drink of alcohol (Q41), marijuana or synthetic marijuana (Q47 & Q48) and prescription pain medication without a prescription or different than for its intended use (Q49). Categorical response options ranged from 0 times over the past 30 days, to 40 or more times. For analysis, we dichotomised each question as never used or used one or more times over the past 30 days, then created an overall composite variable indicating if the participant had used any substances over the past 30 days. The composite variable was used to prevent overfitting of the model and avoid collinearity between substance use questions. A non-composite approach to modelling substance use is included in online supplemental appendix table 4 and returned similar results as the composite approach.

We evaluated illicit drug use via the ABES items asking participants ‘During your life, how many times have you used any form of…’, cocaine/crack (Q50), inhalants (Q51), heroin (Q52), methamphetamines (Q53), ecstasy/3,4-methylenedioxymethamphetamine (MDMA) (Q54) or illegal injectable drugs (Q55). Response options mirror that of the substance use questions and creation of a composite variable was used for analysis, as described above.

Basic demographics such as grade level, biological sex, race and ethnicity were collected on the ABES and included as covariates in the study.

Statistical methods

We first compared differences in demographics between adolescents with concussion in the past 12 months versus adolescents with no concussion history. We also compared physically active (>3 days of physical activity per week) versus inactive (<3 days per week) participants. Physical activity was dichotomised for simple presentation of demographic data but modelled in its true ordinal form in all ensuing analyses. Variables with between-group p values of <0.20 were considered potential confounders. The purpose of including confounders is to accurately estimate the relationship between our primary predictor variable (recent concussion history) and our outcome while accounting for other variables that could distort or bias this relationship.

Logistic regression was used to test the association of self-reported hopelessness with concussion incidence in the past 12 months and physical activity. We also tested whether concussion history modifies the association between physical activity and odds of self-reported hopelessness (concussion×physical activity interaction). First, we constructed an unadjusted logistic regression model containing only the primary explanatory variables (concussion history and physical activity). Then, we constructed a multivariable adjusted model. The adjusted model included all demographic covariates that were associated with concussion history and/or physical activity at an alpha level of p<0.20 in the univariable analysis and/or were identified as plausible confounders based on study team expertise (see tables 1 and 2). Our results and discussion include findings from the final adjusted model, which controlled for covariates. We also examined changes in ORs for the primary explanatory variables throughout intermediate stages of model building to assess how relationships shifted with the inclusion of confounders or other lifestyle factors (ie, substance or illicit drug use).

Table 1.

Distribution of demographics across the concussion groups (n=7499)

	No concussion			One or more concussion(s)
	Freq.	Wt. Freq.	%	Freq.	Wt. Freq.	%	P value
Grade, n (%)							0.1358
9th grade	1777	1707.0	26.3	232	215.5	31.8
10th grade	1642	1638.0	25.2	181	175.2	25.8
11th grade	1558	1567.0	24.1	171	160.2	23.6
12th grade	1481	1589.0	24.4	139	127.0	18.7
Female sex, n (%)	3460	3375.0	52.1	318	303.5	44.8	0.0147
≥3 days of physical activity	3190	3188.0	49.3	466	428.1	63.6	<0.0001
Race/ethnicity, n (%)							0.6870
Am Indian/Alaska Native	67	40.0	0.6	10	6.8	1.0
Asian	309	342.8	5.3	27	24.4	3.6
Black or African American	955	778.9	12.1	106	84.1	12.5
Native Hawaiian/other PI	25	32.4	0.5	4	5.2	0.8
White	2933	3250.0	50.3	344	349.7	51.9
Hispanic/Latino	511	515.5	8.0	54	56.0	8.3
Multiple—Hispanic	1215	1141.0	17.7	126	105.8	15.7
Multiple—non-Hispanic	393	358.6	5.6	45	42.1	6.2
Obesity*, n (%)	1105	1167.0	19.7	138	136.7	22.3	0.2634
Recent alcohol use, n (%)	1108	1137.0	18.5	202	186.5	31.7	<0.0001
Recent marijuana use, n (%)	827	744.0	11.6	167	149.7	22.4	<0.0001
Recent synthetic marijuana use, n (%)	347	312.1	4.8	98	89.5	13.3	<0.0001
Recent prescription pain use, n (%)†	266	230.2	3.6	96	78.3	11.6	<0.0001
Recent nicotine use, n (%)‡	940	914.0	14.1	203	183.0	27.0	<0.0001
Ever used illicit drugs, n (%)§	459	425.1	6.5	131	127.4	18.8	<0.0001

P value based on the Rao-Scott Chi-Square test.

^*Obese=BMI percentile is at or above the 95th, percentile for BMI by age and sex. Recent use=any use (1 or more times) in the previous 30 days.

^†Prescription pain use (Q94)=During the past 30 days, how many times did you take prescription pain medicine without a doctor’s prescription or differently than how a doctor told you to use it?.

^‡Composite variable that includes cigarettes, cigars, smokeless tobacco and/or vaping.

^§Ever used illicit drugs is a composite variable that includes cocaine, inhalant(s), heroin, methamphetamine, MDMA or injection drug use.

BMI, body mass index; MDMA, 3,4-methylenedioxymethamphetamine.

Table 2.

Distribution of demographics across the physical activity groups

	≤3 days of physical activity			>3 days of physical activity
	Freq.	Wt. Freq.	%	Freq.	Wt. Freq.	%	P value
Grade, n (%)							0.3137
9th grade	934	902.3	25.4	1090	1027.0	28.1
10th grade	913	910.3	25.6	917	910.9	24.9
11th grade	865	884.9	24.9	873	847.5	23.2
12th grade	813	853.4	24.0	815	868.5	23.8
One or more concussions, n (%)	252	244.7	6.9	466	428.1	11.8	<0.0001
Female sex, n (%)	2121	2066.0	58.5	1669	1614.0	44.2	<0.0001
Race/ethnicity, n (%)							<0.0001
Am Indian/Alaska Native	37	25.5	0.7	41	22.4	0.6
Asian	202	214.3	6.1	131	152.3	4.2
Black or African American	609	480.6	13.6	465	388.8	10.7
Native Hawaiian/other PI	22	26.3	0.8	7	11.3	0.3
White	1415	1616.0	45.8	1877	1982.0	54.6
Hispanic/Latino	299	298.9	8.5	263	273.5	7.5
Multiple—Hispanic	694	669.2	18.9	658	586.2	16.1
Multiple—non-Hispanic	216	193.9	5.5	226	213.9	5.9
Obesity*, n (%)	698	721.8	22.9	558	591.9	17.3	<0.0001
Recent alcohol use, n (%)	608	637.1	19.3	710	690.5	20.1	0.4522
Recent marijuana use, n (%)	474	421.8	12.0	532	479.9	13.3	0.2770
Recent synthetic marijuana use, n (%)	223	193.7	5.5	224	208.4	5.7	0.6355
Recent prescription pain use, n (%)†	192	152.4	4.3	171	151.2	4.2	0.7898
Recent nicotine use, n (%)‡	535	533.5	15.0	619	574.4	15.7	0.5346
Ever used illicit drugs, n (%)§	311	310.9	8.8	287	244.0	6.7	0.0506

P value based on the Rao-Scott χ² test.

^*Obese=BMI percentile is at or above the 95th, percentile for BMI by age and sex. Recent use=any use (1 or more times) in the previous 30 days.

^†Prescription pain use (Q94)=During the past 30 days, how many times did you take prescription pain medicine without a doctor’s prescription or differently than how a doctor told you to use it?.

^‡A composite variable that includes cigarettes, cigars, smokeless tobacco and/or vaping.

^§Ever used illicit drugs is a composite variable that includes cocaine, inhalant(s), heroin, methamphetamine, MDMA or injection drug use.

BMI, body mass index; MDMA, 3,4-methylenedioxymethamphetamine.

The complex survey design was accounted for using the ‘procsurveyfreq’, ‘procsurveymeans’ and ‘procsurvey-logistic’ procedures in SAS V.9.4. The jackknife residual method was used to estimate standard errors in all logistic models. We assessed logistic regression assumptions, including linearity. Custom SAS processing, formatting and analysis programmes are available on our GitHub page, https://github.com/CU-Department-of-Orthopedics.

RESULTS

Study population

The total sample included 7499 adolescents (table 1). The crude prevalence of feelings of hopelessness/sadness in the sample was 44.2% (95% CI: 41.6% to 46.8%). The prevalence of one or more concussions over the prior 12 months was 9.4% (95% CI: 8.2% to 10.7%) and approximately half (50.7%; 95% CI: 47.8% to 53.6%) of the sample reported >60 min of physical activity more than 3 days per week. See online supplemental appendix tables 1-3 for more information about physical activity, recent mental health status and concussion history in the sample.

Demographic confounders

There was a difference in the proportion of grade, physical activity and substance use between individuals who reported a history of one or more concussions versus individuals who reported no concussions over the previous 12 months (table 1). Concussion history, sex, obesity and race/ethnicity were significantly different between individuals who engaged in physical activity >3 days per week versus individuals who were physically active <3 days per week (table 2).

Unadjusted models

The unadjusted models investigated associations between self-reported depressive symptoms and recent concussion history (ie, in the 12 months prior to survey completion) or self-reported physical activity. Adolescents with one or more concussions in the last year had 1.41 times greater odds (95% CI: 1.17 to 1.71) of reporting sadness/hopelessness compared with peers without concussions in the last year. Independent of concussion, each additional day that participants were physically active for >60 min was associated with 0.89 times odds (95% CI: 0.87 to 0.91) of reporting depressive symptoms (figure 1).

Figure 1.

Relationship between increasing number of physically active days per week and decreasing probability of reporting feelings of hopelessness/sadness over the prior year. The probability estimates and 95% CIs were obtained from a logistic regression model testing the association between increasing physical activity over the prior 7 days and odds of feelings of hopelessness/sadness over the prior year. Physical activity was defined as total number of days over the week prior to survey completion in which individuals were physically active for a total of at least 60 min per day.

Effect modification: concussion and physical activity

We also tested whether concussion history modifies the association between physical activity and odds of reporting depressive symptoms. Concussion history did not significantly modify the association between physical activity (p=0.6086) and odds of reporting depressive symptoms. Physical activity was protective against odds of depressive symptoms among individuals who reported one or more concussions over the previous year (OR: 0.89, 95% CI: 0.82 to 0.97) as well as individuals who reported no concussions over the previous year (OR: 0.91, 95% CI: 0.89 to 0.94, figure 2).

Figure 2.

Inter-relationship between physical activity (PA), concussion history and odds of hopelessness/sadness over the previous year. The y-axis represents odds of feelings of hopelessness/sadness over the prior year for every 1 day increase in PA. The x-axis represents the stratum specific estimates of the adjusted association between PA and feelings of hopelessness/sadness among individuals with no prior history of concussion (middle OR) as well as history of one or more concussions over the prior year (right OR). Although the protective effect of PA was slightly increased in the concussion group, history of a prior concussion did not significantly modify the association between PA and feelings of hopelessness/sadness.

Final adjusted model: illicit drug and substance use

The final multivariable logistic regression model adjusted for concussion history, physical activity, substance use, illicit drug use and covariates of participant grade, biological sex, race/ethnicity and obesity. Increasing physical activity was significantly associated with decreased odds of depressive symptoms (OR per 1-day increase: 0.91; 95% CI: 0.89 to 0.94; p<0.0001). Participants reporting one or more concussions over the past year were not at significantly increased odds of reporting depressive symptoms relative to non-concussed peers (OR: 1.13, 95% CI: 0.93 to 1.37, p=0.2109). Illicit drug use (OR ever vs never: 2.48; 95% CI: 1.96 to 3.13; p<0.0001), substance use in the previous 30 days (OR yes vs no: 2.77; 95% CI: 2.34 to 3.29; p<0.001) and female sex (OR female vs male: 2.64; 95% CI: 2.28 to 3.06; p<0.0001) were associated with higher odds of reporting depressive symptoms. Grade (p=0.3762), obesity (p=0.1080) and race/ethnicity (p=0.1409) were not significantly associated with odds of depressive symptoms in the final model.

Intermediate models

In the unadjusted model, concussion in the last 12 months was associated with feelings of hopelessness/sadness. However, this association was no longer significant after adjusting for illicit drug use and substance use in the final model (table 3). We reviewed intermediate models, defined as a subset of the full list of potential confounding variables, to identify variables or sets of variables that, when added to the model, shifted the concussion OR towards the null and thus, potentially represent important variables that confound the association between concussion history and depressive symptoms. When substance use over the previous 30 days and history of illicit drug use were adjusted for in the model, the OR representing the association between concussion history and feelings of hopelessness/sadness decreased by 23.4% (towards the null).

Table 3.

Summary of model building with primary outcome being odds of sadness/hopelessness

Contrast	OR	LCL	UCL	% change in OR*
Unadjusted model
Concussion vs no concussion	1.41	1.17	1.71	–
Physical activity per 1 day	0.89	0.87	0.91	–
Adjusted model: covariates of grade, sex, obesity and race/ethnicity
Concussion vs no concussion	1.47	1.22	1.79	+4.3%
Physical activity per 1 day	0.91	0.89	0.94	−2.8%
Final adjusted model: covariates, illicit drug and substance use
Concussion vs no concussion	1.13	0.93	1.37	−23.4%
Physical activity per 1 day	0.91	0.89	0.94	−0.2%

Ever used illicit drugs is a composite variable that includes cocaine, inhalant(s), heroin, methamphetamine, MDMA or injection drug use.

Recent substance use is a composite variable based on self-reported use of one of more of the following substances during the previous 30 days: nicotine, alcohol, marijuana, synthetic marijuana, prescription opioid misuse (use of prescription pain meds without a prescription and/or in manner, ie, inconsistent with doctor recommendations).

^*Change in OR represents % change in OR relative to the previous model (adjusted–previous)/adjusted, + values indicate the OR moved away from null (OR=1), − values indicate the OR moved away from the null.

LCL, lower 95% confidence limit; MDMA, 3,4-methylenedioxymethamphetamine; UCL, upper 95% confidence limit.

DISCUSSION

Concussion and mild traumatic brain injury have been proposed as a potential contributor to poor mental health, including feelings of sadness or hopelessness, in past research.^{5 7 8 33} Our study contradicts this notion by introducing lifestyle factors such as physical activity or substance use as important considerations in the relationship between concussion and depressive symptoms. Physical activity or substance use may be helpful or harmful to mental health, respectively, and confound the association between concussion history and depressive symptoms, but the complex inter-relationships between these factors have not been thoroughly investigated in research to date. After adjusting for physical activity, substance use and illicit drug use, we found that concussion history is not significantly associated with depressive symptoms in a representative sample of more than 7000 US adolescents. These data indicate that our understanding of the association between concussion and depression-related mental health symptoms should not be viewed through a singular (univariable) lens, but through a comprehensive and multifaceted approach that accounts for lifestyle behaviour variability and the co-occurrence of risk factors before, during and after concussion which may affect mental health outcomes for adolescents.

Nearly half (approximately 44%) of adolescents in this nationally representative survey reported feeling so sad or hopeless almost every day for 2 weeks or more that they stopped doing some usual activities. This aligns with past work which has described deteriorating adolescent mental health as a substantial public health concern.³⁴ We also identified significantly higher odds of reporting depressive symptoms among female participants compared with male participants. This is consistent with past work in adolescents with concussion which has shown a higher rate of endorsing depressive symptoms among female adolescents compared with males.³⁵ Biological sex may be an important component to consider when understanding the risk of mental health problems in patients with recent concussion.

Our analysis consistently underscored physical activity as a protective factor for adolescent depressive symptoms, aligning with and extending previous suggestions in the literature. The WHO and US CDC both recommend that children and adolescents engage in 60 min of physical activity 7 days per week for a healthy physically active lifestyle.^{36 37} Only 19% of participants included in our analysis met this criterion of self-reported physical activity (online supplemental appendix table 2). Based on our data, a participant engaging in >60 min of physical activity 7 days per week would be 32% less likely to report depressive symptoms compared with a participant physically active for 3 days per week, regardless of concussion status. Though, the directionality and temporality of this association cannot be determined through our study design; it is unknown if physical activity necessarily affected sadness/hopelessness, or if feeling sad/hopeless precluded physical activity. Past work in patients with concussion with acute and persisting symptoms suggests that physical activity may be one treatment option to address postinjury anxiety and depressive symptoms.^21-23 More research may be necessary to validate these same approaches in patients further from injury, such as those who sustained a concussion months to years previously.

Notably, our findings reveal a higher prevalence of substance and illicit drug use among adolescents with a concussion history than those without. Almost one in five adolescents with a history of concussion reported illicit drug use. Drug and/or substance use in adolescence has been associated with worse mental health, independent of concussion status.¹⁹ Our investigation built on this, finding that adolescents who reported substance use in the past 30 days were approximately 2–3 times (OR: 2.77) more likely to report depressive symptoms than peers who did not report substance use. Adolescents who used illicit drugs were similarly two-and-a-half times (OR: 2.48) more likely to report sadness/hopelessness compared with peers. The collinearity of concussion history and substance use remains poorly explored; it is unclear if concussion is an immediate risk factor for substance use, or if substance use is a lifestyle/behavioural factor tangentially associated with an increased risk for sustaining a concussion.

An interesting finding of our investigation was the change in OR between the unadjusted and adjusted models for the association between concussion history and participant reporting of depressive symptoms. When controlling for substance and illicit drug use and other covariates, the OR representing the relationship between concussion history and depressive symptoms decreased substantially towards the null hypothesis. Scientifically, this may indicate that the associations observed between concussion and depressive mental health are more thoroughly explained by differences in substance use behaviours than by concussion history alone. Clinically, these results further support the complexity and multifaceted nature of mental health in adolescent populations, particularly among those who have experienced a concussion.

When substance use questions were investigated individually (ie, non-composite; see online supplemental appendix table 4), misuse of prescription pain medication was associated with the greatest odds of depressive symptoms compared with other substances, such as alcohol, marijuana or nicotine. Prescription pain medication use has been indicated in higher severity traumatic brain injury but has not been thoroughly investigated within the context of concussion.³⁸ Though this finding is outside the scope of our singular investigation, these data indicate the importance of assessing an array of lifestyle factors, including (but not limited to) physical activity and substance use, in addition to recent concussion status, to obtain a holistic understanding of patients and inform treatment pathways. Both scientifically and clinically, our results point to methods that guide patients towards more physical activity and less substance use as strategies to reduce negative depression-related mental health sequelae associated with concussion.

Limitations

This study has notable strengths and limitations which should be considered when interpreting our results. First, we leveraged data from the ABES, a robust, nationally representative questionnaire that used a stratified, three-stage cluster probability-based design and enrolled >7000 adolescent-aged high school students across diverse public and private schools in the USA. In addition, weighted frequencies were applied to account for random sampling error (see the ‘Statistical methods’ section). Thus, the results of our investigation have strong generalisability for adolescents within the USA but may not generalise to individuals outside of the USA.

Our investigation is cross-sectional and limits our capacity to determine causality. It is unclear whether concussion predisposed individuals to substance use or physical activity/inactivity, or if worse mental health is a risk factor for substance use or physical inactivity. Determining the directionality of these relationships will be essential in future prospective investigations. A lack of consistency in the time frame for various questions should also be considered. For example, concussion history was reported for the previous 12 months, substance use was reported for the previous 30 days and physical activity was reported for only the previous week. In addition, the ABES survey provides only crude assessments of mental and physical health. For example, the ABES measure of physical activity is limited in that it lacks detailed information on the duration, intensity and type of activities performed. Large-scale, nationally representative surveys such as the ABES often do not capture such granular data.

We relied on a single measure of depressive symptoms, question 25 in the ABES survey asking about feelings of sadness and hopelessness. The ABES offers several mental-health-related items from which to choose, including questions related to suicidal ideation and attempts. Sadness/hopelessness may be an ideal outcome for investigation because it represents a subclinical manifestation of mental health symptoms. Recent narrative reviews have indicated that anxiety and depressive symptoms may appear postconcussion, though are quick to note that levels often exist subclinically. Regardless, we repeated our same analysis approach with question 85 (Q85) ‘during the past 30 days, how often was your mental health not good?’ (online supplemental appendix table 1). The obtained results did not differ from that which we present in this manuscript.

Unmeasured confounding is a limitation of this study. Though we adjusted for possible covariates, there may be other relevant factors that were not evaluated, such as clinical characteristics, socioeconomic status or environmental influences, that introduced bias into our estimates. Furthermore, we tested for effect modification on the multiplicative scale only (ORs). It is possible that concussion history modified the association between physical activity and prevalence of depressive symptoms on the additive scale (risk differences).

Last, the ABES survey was administered during the COVID-19 pandemic, which may have influenced our findings. For example, the documented reduction in sport and physical activity participation during the pandemic may have reduced the incidence of concussion in our sample. Similarly, the pandemic may have introduced unique circumstances that impacted adolescent mental health in ways that are both unknown and difficult to quantify.

CONCLUSIONS

The relationship between recent concussion history and depression-related mental health symptoms among adolescents is complex and likely affected by several lifestyle factors. After adjusting for physical activity behaviours, substance use and illicit drug use, concussion history had a minimal, non-significant, effect on feelings of sadness or hopelessness in a nationally representative sample of adolescents. Our findings also highlight the critical role of physical activity as a protective factor against depressive symptoms. We identified a complex inter-relationship between depressive symptoms, concussion history and substance use. Although concussion history was not significantly associated with depressive symptoms, adolescents with concussion history were more likely to report substance use, a strong risk factor for poor mental health. These results underscore the need for holistic approaches in clinical assessment and intervention for adolescents with a history of concussion, emphasising the importance of promoting physical activity and monitoring for substance use as well as depressive symptoms during recovery. Future research should aim to explore these relationships through longitudinal designs to better understand causality rather than simple association and inform targeted interventions for improving adolescent mental health in the context of concussion recovery.

Supplementary Material

Supplemental material This content has been supplied by the author(s). It has not been vetted by BMJ Publishing Group Limited (BMJ) and may not have been peer-reviewed. Any opinions or recommendations discussed are solely those of the author(s) and are not endorsed by BMJ. BMJ disclaims all liability and responsibility arising from any reliance placed on the content. Where the content includes any translated material, BMJ does not warrant the accuracy and reliability of the translations (including but not limited to local regulations, clinical guidelines, terminology, drug names and drug dosages), and is not responsible for any error and/or omissions arising from translation and adaptation or otherwise.

Additional supplemental material is published online only. To view, please visit the journal online (https://doi.org/10.1136/bjsports-2024-109029).

WHAT IS ALREADY KNOWN ON THIS TOPIC

• Adolescents who sustain a concussion are at increased risk of mental health disturbances, including anxiety and depressive symptoms. Lifestyle factors which influence this relationship remain unknown.

WHAT THIS STUDY ADDS

• This study identified physical activity as a protective factor and substance/illicit drug use as risk factors for depressive symptoms in adolescents. After controlling for physical activity and substance/illicit drug use, concussion history was no longer associated with depressive symptoms. These results provide a holistic perspective for clinicians counselling adolescents with a history of concussion.

HOW THIS STUDY MIGHT AFFECT RESEARCH, PRACTICE OR POLICY

• Physical activity and substance/illicit drug use, but not concussion history, are associated with adolescent depressive symptoms. This novel discovery assists clinicians caring for adolescents with concussions, improving postinjury recommendations by informing patients of factors which may relate to the risk of adverse mental health outcomes.

Data availability statement

Data are available in a public, open access repository. We analysed data from the Adolescent Behaviour and Experiences Survey (ABES), a nationally representative survey of health and behavioural-related outcomes among adolescents. The ABES is a stratified, three-stage cluster probability-based survey which enrolled adolescent-aged high school students in public and private schools across the USA.