Exposure to repetitive head impacts (RHI) through participation in contact and collision sports (CCS) can result
in symptomatic concussions and asymptomatic subconcussions and may increase risk for later-life cognitive
decline and neuropsychiatric dysfunction, as well as dementia from neurodegenerative disease, including
chronic traumatic encephalopathy. Despite many scientific advances in this area, critical knowledge gaps exist
due to: small samples, cross-sectional designs, focus on male professional American football players,
recruitment biases, and reliance on retrospective reports from informants. Many questions remain, such as: What
aspects of RHI are most pertinent to these risks? Are there non-RHI factors that enhance or mitigate risk? Do
the risks generalize to women and to soccer players? Our goal is to address these limitations and examine risk
factors for, and characterize the frequency, severity, and profile of cognitive impairment, neurobehavioral
dysregulation (e.g., explosiveness, impulsivity, “short fuse”), and dementia, in female and male former soccer
players and male former American football players. We will create the Head Impact and Trauma Surveillance
Study (HITSS) by leveraging the Brain Health Registry (BHR) at the University of California, San Francisco. BHR
is an online registry for the longitudinal study of people interested in participating in Alzheimer’s disease (AD)
and related dementias (ADRD) research, with ~70,000 participants currently enrolled. BHR participants complete
demographic and health questionnaires, medical and neurologic histories, depression scales, subjective
cognitive complaint measures, and two validated online cognitive tests. They can also have a study partner
complete additional online measures of the participant’s cognitive and functional status and neuropsychiatric
symptoms. A HITSS Module will be developed and added to BHR to assess CCS history, RHI exposure (e.g.,
positions played, age of first exposure, duration of play, era of play, soccer heading), and standardized
neuropsychiatric measures. Participants will be recruited into HITSS through an extensive national advertising
and social media outreach. We will enroll 1800 former soccer (900 female, 900 male) and 1800 male former
American football players into HITSS, across levels of play (high school, college, or elite/professional), ages 40-
75. Using the existing BHR dataset, two comparison groups (n = 1800 each) of current BHR participants without
a CCS or TBI history will be propensity-matched to the former soccer and former American football players. We
will test the hypothesis that greater cumulative RHI exposure from soccer and American football increases risk
for cognitive impairment, neurobehavioral dysregulation, and dementia, and that non-RHI factors (e.g., TBI
history, sex, race, vascular risk, cognitive reserve) will modify the effect. Data will be shared with researchers
worldwide. Findings will advance research on risk of later-life cognitive decline, neurobehavioral dysregulation,
and dementia from CCS involvement. Development of HITSS will also create: (1) a self-sustaining mechanism
for follow-up of participants in other CCS studies; (2) a longitudinal, sharable dataset of thousands of female and
male, active and former CCS athletes; and (3) a readiness registry of CCS athletes for future research.
