Chronic cannabis use may protect young adult athletes from the effects of subconcussive head impacts
By Fadhil Hussain. This article was initially published in the 8/24/23 edition of our Concussion Update newsletter; please consider subscribing.
Cannabis use is becoming more common in athletics as cannabis legalization increases and restrictions loosen in sports leagues. Kalbfell et al. aimed to discover whether chronic cannabis use would protect the brain from acute subconcussive head impacts or worsen their effects. The key findings showed that players who used cannabis regularly had better eye focus ability and lower levels of brain inflammation compared to the non-cannabis group after repetitive head impacts. The findings, published in iScience, suggest that chronic cannabis use may deter some of the adverse effects that athletes experience from subconcussive head impacts in contact sports.
This case-control study included 43 adult soccer players, aged 20 on average, of whom 24 self-reported cannabis use at least once per week over the last six months, and 19 did not use cannabis. Both groups headed a soccer ball twenty times under controlled conditions. The researchers measured participants before the headings to establish a baseline and then at 2 hours, 24 hours, and 72 hours post-heading. The primary outcome measure was near-point of convergence (NPC), which is the closest point that a person’s eyes can focus on before vision gets blurry. Additionally, the authors drew blood to measure serum levels of S100B to gauge astrocyte activation (involved in the inflammatory response after a head impact) and neurofilament light chain (NfL––to gauge damage to axons of neurons).
In the control group, “NPC continued to increase at least up to 72 hours post 20 headings, while such NPC elevation plateaued after 24 hours in the cannabis group,” suggesting a worse ability of the eye’s muscles to adjust focus on nearby objects in the control group compared to the cannabis group. The difference between the groups was even greater in serum S100B levels. S100B increased linearly over all three time points in the control group but showed almost no change in the cannabis group. This blood biomarker finding suggests a decreased inflammatory response in the players who regularly used cannabis. Damage to axons measured by NfL showed no statistically significant within-group or between-group differences after the 20 headings.
Cannabis use has been studied in various contexts, but this study isolated the effects of head impacts to understand their interactions with cannabis use while limiting potential confounding factors. The results demonstrate that chronic cannabis use in young adult athletes may have neuroprotective benefits. The authors note that “a future study in a field setting is warranted to test the translatability of [their] findings.” Additionally, a randomized controlled trial, which faces regulatory barriers since cannabis and cannabinoids are scheduled substances under the Controlled Substance Act, could help scientists further understand the relationship between cannabis use and head impacts. Lastly, long-term studies could be beneficial to see if chronic cannabis use provides any protection from neurodegenerative diseases such as chronic traumatic encephalopathy, the development of which is driven primarily by repeated subconcussive head impacts.
