From Pages to Practice
As a team physician for a professional soccer team, I have the vantage point on game days to observe the exciting actions that occur on the pitch (field) from the sideline of the most popular sport in the world. Unfortunately, this also means that I witness first-hand the occasional sports-related traumatic brain injuries (TBIs) that occur on game days.
In contact sports, repetitive head injuries are not uncommon. In the United States, as many as 3.8 million cases of sports-related TBIs are estimated to occur annually. TBIs are often caused by sudden direct impact or other forces that propel the skull, leading to rotational acceleration and deceleration injury to the brain. Sports-related TBIs can present as concussions, which are short-lived neurological impairments (80%–90% of sports-related concussions resolve within 10 days). TBIs can also result in chronic traumatic encephalopathy, which is a neurodegenerative condition resulting from repeated head injuries. Such injuries are associated with increases in tau proteins in the brain and may present with cognitive, emotional, and psychiatric changes.
While American football has been associated with increased risk of chronic traumatic encephalopathy, it is unclear whether soccer, played by more than 265 million people in the world, is associated with increased risk for neurodegenerative conditions due to repetitive head injuries.
In a study published in NEJM, Mackay and colleagues report the results of a retrospective cohort study that compared mortality rates due to neurodegenerative diseases in about 7,600 former professional soccer players in Scotland and about 23,000 controls in the general population. The results indicated that the mortality rate (2.9% vs. 1.0%) was about 3.5 times higher in former professional soccer players (adjusted hazard ratio, 3.45; 95% CI, 2.11–5.62; P<0.001).
Does this mean that nonprofessional soccer players should stop playing? In an editorial, Robert A. Stern from the Boston University School of Medicine agrees with the study authors, noting “it is not possible to generalize their findings among male former professional soccer players to participants in recreational, amateur, or collegiate-level soccer. Parents of children who headed the ball in youth or high-school soccer should not fear that their children are destined to have cognitive decline and dementia later in life. Rather, they should focus on the substantial health benefits from exercise and participation in a sport that their children enjoy. However, it is also important that the findings from the current study lead to research and increased awareness of the potential short-term and long-term consequences of heading the ball in amateur soccer”.
The following NEJM Journal Watch summary provides more details of the study.
Jaime Toro, MD reviewing Mackay DF et al. N Engl J Med 2019 Nov 7 Stern RA. N Engl J Med 2019 Nov 7
Although exercise and sports are beneficial for health and for preventing dementia, some contact and collision sports may increase cognitive decline and cause chronic traumatic encephalopathy and dementia. Repetitive head impacts seem to be associated with neuropathologic changes and biomarkers such as deposits of hyperphosphorylated tau protein and neurofibrillary tangles.
In this retrospective cohort study, researchers compared mortality from neurodegenerative disease in 7676 former soccer players with mortality in controls from the general population matched by sex, birth year, and extent of social deprivation.
Mortality from nonneurologic diseases was lower in soccer players than among controls.
Nevertheless, mortality from neurodegenerative diseases was 1.7% in soccer players and 0.5% in controls, and prescriptions for dementia medications were more common in former soccer players.
Comment: Although this is an excellent study with a significant number of participants and results similar to other studies published previously (NEJM JW Neurol Oct 2017 and JAMA Neurol 2017; 74:909), other prospective, matched, controlled studies must be performed to confirm these findings. As an editorialist notes, these results cannot be generalized to young people playing contact sports, which have important health benefits; but the cumulative effects of head impacts in amateur and professional sports should be studied.