Cognitive and Behavioral Functioning in Female Former Soccer Players: Results from the Head Impact and Trauma Surveillance Study (HITSS)

This cross-sectional study of 3,174 female former soccer players found that higher cumulative exposure to repetitive head impacts was significantly associated with increased subjective cognitive complaints, behavioral dysregulation, and depressive symptoms, but showed no association with objective cognitive performance.

The Gist

Imagine a massive library of stories about women who spent their youth and young adulthood playing soccer. For years, we've been worried that the constant, repetitive "thwack" of heading the ball might be like a slow leak in a tire, eventually causing problems later in life. But most of the research so far has been about men playing American football. We didn't have a clear picture of what happens to the women who played soccer.

This study is like opening the doors to that library and reading the stories of 3,174 women (all over 40 years old) to see if their soccer history left any marks on their brains today.

Here is the story of what they found, broken down into simple analogies:

1. The "Headache" vs. The "Test"

The researchers asked these women two types of questions:

• The "How do you feel?" questions: "Do you feel forgetful?" "Do you feel moody or easily frustrated?" "Are you feeling down?" (These are like asking a driver, "Does the car feel sluggish?")
• The "Show me what you can do" tests: Computer games that test memory and planning. (These are like putting the car on a dynamometer to measure its actual horsepower).

The Twist: The women who played soccer the longest, at the highest levels, and headed the ball the most often reported feeling worse on the "How do you feel?" questions. They felt more forgetful, more irritable, and more depressed.

However, when they took the computer tests, they performed just as well as anyone else. It's as if the drivers said, "My car feels like it's dragging," but when they put it on the test track, it ran perfectly fine.

2. The "Dose-Response" Ladder

The study found a clear pattern, like climbing a ladder:

• Youth players (who played the least) felt the best.
• High school and College players felt a little worse.
• Professional players (the ones who played the longest and headed the ball the most) felt the worst.

The more "exposure" a woman had to the sport—measured by how many years she played, how high the level was, and how often she headed the ball—the more likely she was to report symptoms of brain fog, emotional outbursts, or sadness.

3. The "Subjective" vs. "Objective" Gap

Why the difference between feeling bad and testing well? The authors suggest a few reasons:

• The "Early Warning System": Sometimes, the brain's "check engine light" (how you feel) turns on before the engine actually breaks down (failing a test). These women might be in the early stages of changes that haven't yet affected their ability to solve puzzles on a computer.
• The "Mood" Factor: Depression and anxiety can make you feel like your memory is failing, even if your memory is actually fine. The study found that women with more soccer exposure reported more depressive symptoms, which often clouds how we perceive our own abilities.
• The "Test" Limitations: The computer tests used were very specific. They might be like a speed test for a race car, but they don't test how the car handles a bumpy road in the rain. The tests might not be sensitive enough to catch the specific type of "bumpiness" caused by years of heading soccer balls.

4. The Big Picture

Think of this study as a smoke alarm. It's not saying the house is on fire yet (no one failed the memory tests), but the alarm is beeping (people are feeling symptoms).

• The Good News: We found a link between soccer and these feelings, which helps us understand the risks better.
• The Bad News: We don't know why yet. Is it the heading? Is it the concussions? Is it something else?
• The Future: The researchers say we need to keep watching these women over time. Just like checking a car every year, we need to see if these "feeling bad" symptoms eventually turn into actual "engine trouble" (dementia or cognitive decline) as they get older.

The Takeaway

For the millions of women who played soccer, especially those who headed the ball a lot, this study is a gentle nudge. It suggests that while their brains might still be sharp on a computer test, their daily lives might be feeling a bit heavier or foggy. It's a call to pay attention to mental health and mood, and a reminder that we need to keep studying women in sports to make sure we understand the full story.

Technical Summary

1. Problem Statement

Repetitive head impacts (RHI) from contact sports are linked to later-life cognitive impairment, neurobehavioral dysregulation, and neurodegenerative diseases like Chronic Traumatic Encephalopathy (CTE). While extensive research exists on male American football players, the long-term consequences of RHI in female soccer players remain poorly understood.

• The Gap: Existing literature is predominantly male-focused. Female athletes may face unique risks due to anatomical differences (e.g., neck strength) and hormonal influences (estrogen/progesterone fluctuations) that modulate neuroinflammatory responses.
• The Conflict: Previous studies on female soccer players have yielded mixed results regarding cognitive decline, with some showing deficits in memory and speed, while others showing no adverse effects compared to controls.
• Objective: This study aimed to examine the relationship between proxies of RHI exposure (duration of play, level of play, and estimated cumulative heading frequency) and clinical outcomes (subjective cognitive complaints, objective cognitive performance, behavioral dysregulation, and depressive symptoms) in a large cohort of women aged 40 and older.

2. Methodology

Study Design & Population:

• Study: A cross-sectional analysis of data from the Head Impact and Trauma Surveillance Study (HITSS), an extension of the UCSF Brain Health Registry.
• Cohort: 3,174 female former soccer players (mean age 47.15 years).
• Inclusion Criteria: Self-identified as female, soccer as primary sport, no longer playing, age $\ge$ 40, and completion of at least one outcome measure.
• Levels of Play: Spanned Youth (136), High School (1,786), College (1,046), and Professional/Semi-professional (206).

Exposure Metrics (RHI Proxies):
Derived from the Boston University Repetitive Head Impact Exposure Assessment (RHIEA):

1. Total Years of Play: Cumulative duration of organized soccer.
2. Highest Level of Play: Categorized as Youth, High School, College, or Professional.
3. Estimated Cumulative Heading Frequency: Calculated by summing self-reported frequency of heading (Less, As, More frequently than peers) across all levels of play (range 0–15).

Outcome Measures:

• Subjective Cognitive Complaints:
  • BRIEF-A Metacognition Index (MI): Executive functioning (Initiate, Working Memory, Plan/Organize, etc.).
  • Everyday Cognition Scale (ECog): Perceived decline in daily tasks compared to 10 years prior.
• Behavioral & Depressive Symptoms:
  • BRIEF-A Behavioral Regulation Index (BRI): Impulse control, emotional regulation.
  • Geriatric Depression Scale (GDS-15): Depressive symptom severity.
  • Mild Behavioral Impairment Checklist (MBI-C): Persistent behavioral changes.
• Objective Cognitive Performance (Computerized CANTAB Tests):
  • Paired Associates Learning (PAL): Episodic memory/visual learning.
  • One Touch Stockings (OTS): Spatial planning/problem-solving.
  • Spatial Working Memory (SWM): Working memory and strategy.

Statistical Analysis:

• Models: Multivariable linear regression (for continuous outcomes) and binary logistic regression (for clinically meaningful impairment).
• Adjustments: Models were adjusted for age and years of education.
• Correction: P-values were adjusted using the Benjamini-Hochberg False Discovery Rate (FDR) method to control for multiple comparisons across domains.
• Software: R (v4.5.1) and SPSS (v29.0.2.0).

3. Key Results

A. Subjective and Behavioral Outcomes (Significant Associations)
There were statistically significant, small-to-moderate associations between higher RHI exposure and worse self-reported outcomes:

• Cumulative Heading: Strongest predictor. Associated with worse scores on BRIEF-A (both MI and BRI), GDS-15, MBI-C, and ECog.
  • Clinical Relevance: Higher heading exposure increased the odds of clinically meaningful impairment (e.g., OR 1.14 for BRIEF-A BRI; OR 1.09 for GDS-15).
• Years of Play: Longer duration was associated with greater behavioral dysregulation (BRIEF-A BRI), depressive symptoms (GDS-15), and subjective cognitive decline (ECog).
• Level of Play: A dose-response pattern was observed. Professional players scored significantly worse than Youth and High School players on GDS-15, BRIEF-A BRI, and MBI-C.
  • Key Finding: Professional players had 3.51 times the odds of clinically meaningful impairment on the BRIEF-A BRI compared to youth players.

B. Objective Cognitive Outcomes (Null Findings)

• No Associations: There were no significant associations between any RHI proxy (years, level, or heading) and performance on the objective CANTAB computerized tests (PAL, OTS, SWM).
• Completion Rates: Objective test completion was lower than self-report measures (e.g., only ~30% of the cohort completed the CANTAB tests), potentially introducing selection bias toward cognitively unimpaired participants.

4. Key Contributions

1. Largest Female Soccer Cohort: This represents the largest investigation to date of clinical symptoms and RHI exposure specifically in middle-aged female former soccer players.
2. Differentiation of Subjective vs. Objective: The study highlights a critical dissociation: RHI exposure is significantly linked to subjective cognitive decline, behavioral dysregulation, and depression, but not to objective computerized cognitive test performance in this specific age group.
3. Quantification of Heading Risk: It provides empirical evidence that estimated cumulative heading frequency is a sensitive predictor of neurobehavioral symptoms in women, independent of total years played.
4. Level of Play Gradient: It establishes a dose-response relationship where professional-level play carries the highest risk for behavioral and depressive symptoms compared to lower levels of play.

5. Significance and Implications

• Clinical Relevance: The findings suggest that for female former soccer players, the primary clinical manifestation of RHI exposure in middle age may be neurobehavioral (depression, impulsivity, emotional lability) and subjective cognitive decline, rather than overt objective cognitive failure. This aligns with the clinical features of Traumatic Encephalopathy Syndrome (TES).
• Sex-Specific Vulnerability: The results support the hypothesis that women may have differential vulnerability to head impacts, potentially due to hormonal or anatomical factors, necessitating sex-specific monitoring and safety protocols.
• Limitations & Future Directions:
  • The lack of objective findings may be due to the cohort being relatively young (mean age 47) and cognitively intact, or due to the insensitivity of current computerized tests to early RHI pathology.
  • The study relies on self-reported exposure metrics (no accelerometer data for soccer exists at this scale).
  • Future Work: Longitudinal monitoring is required to determine if these subjective complaints progress to objective decline or neurodegenerative disease (e.g., CTE, Alzheimer's) as the cohort ages.
• Policy Context: With the exponential growth of female soccer participation post-Title IX, understanding these long-term consequences is critical for developing safety guidelines (e.g., heading restrictions) and clinical care pathways for aging female athletes.

Conclusion:
The study concludes that cumulative RHI exposure in female former soccer players is significantly associated with small but statistically significant increases in subjective cognitive complaints, behavioral dysregulation, and depressive symptoms. However, these exposures did not correlate with objective cognitive test performance in this cross-sectional snapshot, underscoring the need for longitudinal studies to track the evolution of these symptoms into potential neurodegenerative conditions.