New study suggests 3 in 4 former NFL players who died from 2008 to 2023 had CTE

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A new study estimates about 3 in 4 former National Football League players who died between 2008 and 2023 had chronic traumatic encephalopathy — an even higher level than identified in another recent study of former players.

The new study , published Wednesday in the journal JAMA Network Open, aimed to provide a clearer view of how many former football players have the progressive neurodegenerative disease.

CTE has been linked to repetitive head impacts that often occur during contact sports such as football, soccer and hockey. CTE has also been detected in the brains of people who were in the military and exposed to traumatic explosions as well as victims of domestic violence. The brain trauma causes an abnormal buildup of the protein tau, and changes in the brain can begin years before symptoms are detected.

CTE can be definitively diagnosed only after death, but it has been associated with symptoms that overlap with dementia such as depression, anxiety, memory loss and lack of impulse control.

Previous studies detected the disease in as many as 99% of former NFL players whose brains had been donated for research. However, a significant limitation of these studies was in their potential bias: They were done in a group of people whose brains had been donated by family members who may have noticed symptoms while the person was still alive.

A study published in August found that at least 1 in 4 former NFL players who died between 2016 and 2021 had CTE. The study compared data from death certificates to determine the number of former professional players who had died against the number of brain donors confirmed to have CTE.

For this new study, Dr. Yorghos Tripodis and other researchers from Boston University’s CTE Center wanted to estimate the prevalence of CTE cases among an even broader group of former professional football players, including those who may not have noticed symptoms or donated their brains for research.

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Soccer, not just American football, may affect long-term brain health

The researchers used data from the Understanding Neurologic Injury and Traumatic Encephalopathy brain bank combined with National Death Index records from former NFL players. They included brain donor and nondonor NFL players who died between January 2008 and December 2023.

Of 2,362 players who died during that time, 396 had donated their brains for research. Among those, 362 — 93.5% — had been diagnosed with CTE. Almost 70% of the players studied died at the age 70 years or older.

The researchers then looked at death certificates for the 2,362 people who died during the time period, finding that former players who had cognitive symptoms related to dementia were five times more likely to have their brains donated. Donations were more likely to come from families of players who had more symptoms or who died at a younger age.

The researchers adjusted the rate of disease among those who donated their brains to consider who was most likely to donate and applied that to the broader population of former players.

When asked about this newest study, the NFL referred to a statement sent in response to the August study: “The NFL continuously strives to make the game of football safer, including by implementing strategies to reduce concussions and head impacts.

“The NFL remains ​committed to ensuring that the NFL community has access to a robust – and expanding – set of resources ​to enhance their physical and mental well being. We encourage former players to utilize these ⁠resources to identify and seek treatment when they are concerned about their health.”

Tripodis said there are limitations to the new research — no study can remove all selection bias and researchers cannot expand the number to populations other than former NFL players. Evidence of CTE in the brain doesn’t mean all players have symptoms.

“Our numbers suggest that the prevalence of dementia, which is the most severe type of cognitive symptoms, is four times higher than the general population among the NFL players,” he said. “The symptoms are high, but doesn’t mean that everybody will have symptoms, doesn’t even mean that everybody with symptoms will have the most severe symptoms at the end of their lives.”

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1 in 4 former NFL players who died from 2016 to 2021 had CTE, study estimates

Dr. Rachel Grashow, a senior research scientist at Harvard University who was not involved in the new research, said the one “tricky” part to the study is understanding why someone donates their brain. She said that if researchers didn’t account for other factors for brain donation, the math “may not be accurate.”

It’s important to separate CTE from dementia, she said. CTE refers to the presence of the protein tau in specific regions in the brain and is measured in stages I through IV. Researchers have found higher rates of dementia among those with stages III and IV CTE only.

“We want to be careful to say that while there are no diagnostic symptoms linked to all of those found to have CTE at all stages, the ones with relatively the most tau protein aggregation show cognitive symptoms — issues with memory, concentration. Cognitive symptoms are different from mood symptoms — depression and anxiety,” Grashow said in an email.

Dr. Julie Stamm, a clinical assistant professor at the University of Wisconsin-Madison, said she was surprised by the high number of presumed CTE cases found in the study after researchers adjusted for who was most likely to donate their brain.

“We talk a lot about the bias of brain banks and how you don’t tend to donate unless you think something’s wrong, and I think that’s been a critique of some of the papers that have come out,” said Stamm, who was not involved with the new research.

Stamm said the NFL can go “a lot farther” in regard to safety to encourage earlier levels of the game to do more, such as not tackling in practices.

“If the NFL says that, the youth levels, the younger levels, they’ll listen, and that will go a long way in decreasing the overall number of impacts over a lifetime that these individuals sustain, which is what we’ve seen increases the risk for CTE,” Stamm said.

Tripodis said that when researchers have a precise estimate of CTE cases from deceased football players, it will motivate them to invest more into research on the disease.

“We’re having significant progress of identifying diagnostic criteria for living patients, designing the clinical trials that will find a cure for the disease,” he said.

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一项新的研究估计，在 2008 年至 2023 年间去世的前美国国家橄榄球联盟球员中，约有 3/4 患有慢性创伤性脑病——这一比例甚至高于最近另一项针对前球员的研究发现的比例。

这项于周三发表在《美国医学会杂志网络公开版》（JAMA Network Open）上的新研究旨在更清楚地了解有多少前足球运动员患有这种进行性神经退行性疾病。

慢性创伤性脑病（CTE）与反复的头部撞击有关，这些撞击通常发生在橄榄球、足球和曲棍球等接触性运动中。在曾服役于军队并经历过爆炸冲击的人员以及家庭暴力受害者的大脑中也检测到了CTE。脑外伤会导致tau蛋白异常积聚，而大脑的变化可能在症状出现前数年就开始发生。

慢性创伤性脑病 (CTE) 只能在死后才能确诊，但它与一些痴呆症的症状有重叠之处，例如抑郁、焦虑、记忆力减退和缺乏冲动控制。

之前的研究在捐献大脑用于研究的前NFL球员中，高达99%的人都检测到了这种疾病。然而，这些研究的一个重大局限性在于其潜在的偏倚：这些研究的对象是那些大脑由家属捐献的人，而家属可能在捐献者生前就注意到了相关症状。

一项发表于8月的研究发现，2016年至2021年间去世的前NFL球员中，至少有四分之一患有慢性创伤性脑病（CTE）。该研究对比了死亡证明数据，以确定去世的前职业球员人数与确诊患有CTE的脑组织捐献者人数。

在这项新研究中，波士顿大学 CTE 中心的 Yorghos Tripodis 博士和其他研究人员希望估算更广泛的前职业橄榄球运动员群体中 CTE 病例的患病率，其中包括那些可能没有注意到症状或捐献大脑用于研究的人。

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足球，而不仅仅是美式橄榄球，可能会影响大脑的长期健康。

研究人员使用了来自“了解神经损伤和创伤性脑病”脑库的数据，并结合了前NFL球员的国家死亡索引记录。他们纳入了2008年1月至2023年12月期间去世的NFL球员，包括捐献大脑的球员和非捐献者。

在那段时间去世的2362名球员中，有396人捐献了大脑用于研究。其中，362人（占93.5%）被诊断患有慢性创伤性脑病（CTE）。近70%的受试球员在70岁或以上去世。

研究人员随后查阅了该时期内2362名死者的死亡证明，发现患有与痴呆症相关的认知症状的前球员捐献大脑的可能性是其他球员的五倍。捐献者更有可能是那些症状更严重或去世时年龄更小的球员的家属。

研究人员调整了捐献大脑者的患病率，以考虑哪些人最有可能捐献大脑，并将此结果应用于更广泛的前运动员群体。

当被问及这项最新研究时，NFL 提到了针对 8 月份研究发表的一份声明：“NFL 不断努力使橄榄球比赛更安全，包括实施减少脑震荡和头部撞击的策略。

“NFL始终致力于确保NFL社区能够获得一系列强大且不断扩展的资源，以提升他们的身心健康。我们鼓励退役球员利用这些资源，在出现健康问题时及时发现并寻求治疗。”

特里波迪斯表示，这项新研究存在局限性——任何研究都无法完全消除选择偏差，研究人员也无法将样本扩展到前NFL球员以外的人群。大脑中存在慢性创伤性脑病（CTE）的证据并不意味着所有球员都会出现症状。

他说：“我们的数据显示，NFL球员中痴呆症（最严重的认知障碍类型）的患病率是普通人群的四倍。症状高发并不意味着每个人都会出现症状，甚至也不意味着所有出现症状的人在生命末期都会出现最严重的症状。”

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研究估计，2016年至2021年间去世的前NFL球员中，四分之一患有慢性创伤性脑病（CTE）。

哈佛大学高级研究科学家瑞秋·格拉肖博士并未参与这项新研究，她表示，这项研究的“难点”在于理解人们捐献大脑的原因。她说，如果研究人员没有考虑到其他影响大脑捐献的因素，那么计算结果“可能并不准确”。

她表示，区分慢性创伤性脑病（CTE）和痴呆症非常重要。CTE指的是大脑特定区域存在tau蛋白，并分为I至IV期。研究人员发现，仅在III期和IV期CTE患者中，痴呆症的发生率较高。

“我们想谨慎地指出，虽然并非所有被诊断患有慢性创伤性脑病（CTE）的患者在所有阶段都会出现特定的诊断症状，但tau蛋白聚集程度相对较高的患者会出现认知症状——记忆力和注意力方面的问题。认知症状与情绪症状——抑郁和焦虑——有所不同，”格拉肖在一封电子邮件中说道。

威斯康星大学麦迪逊分校的临床助理教授朱莉·斯坦姆博士表示，研究人员在调整了最有可能捐献大脑的人群后，发现研究中疑似慢性创伤性脑病 (CTE) 病例数量之多，令她感到惊讶。

“我们经常谈到脑库的偏见，以及人们往往只有在认为大脑出了问题时才会捐献大脑，我认为这一直是对一些已发表论文的批评，”施塔姆说道，他并未参与这项新研究。

斯塔姆表示，NFL 在安全方面可以“走得更远”，鼓励比赛的早期阶段采取更多措施，例如在训练中不进行擒抱。

“如果 NFL 这么说，那么青少年球员，更年轻的球员，他们就会听进去，这将大大有助于减少这些人一生中遭受的冲击总数，而我们已经看到，冲击会增加患 CTE 的风险，”Stamm 说。

特里波迪斯表示，当研究人员能够精确估计已故橄榄球运动员的 CTE 病例数时，这将激励他们投入更多资金进行该疾病的研究。

他说：“我们在确定活体患者的诊断标准、设计能够找到治愈这种疾病方法的临床试验方面取得了重大进展。”