アメフトはALSリスクである

アメフトはALSリスクでもある

Chronic traumatic encephalopathy (CTE)との関連で行われた後ろ向きコホート研究で、アメフトは筋萎縮性側索硬化症のリスクでもあることが明らかとなった。
Association Between Playing American Football in the National Football League and Long-term Mortality. JAMA. Published online February 1, 2018

1982-1992年にアメリカンフットボール選手となった3812人（レギュラー選手2933人、非レギュラー選手879人）の2016年12月までのデータを見返したところ、レギュラー選手2933人の全死亡率（4.9％）は、1987年のストライキ中にほんの数回選手となった879人（4.2％）と有意差はなかった。

Results Of the 3812 men included in this study (mean [SD] age at first NFL activity, 23.4 [1.5] years), there were 2933 career NFL players (median NFL tenure, 5 seasons [interquartile range {IQR}, 2-8]; median follow-up, 30 years [IQR, 27-33]) and 879 replacement players (median NFL tenure, 1 season [IQR, 1-1]; median follow-up, 31 years [IQR, 30-33]). At the end of follow-up, 144 NFL players (4.9%) and 37 replacement players (4.2%) were deceased (adjusted absolute risk difference, 1.0% [95% CI, －0.7% to 2.7%]; P = .25). The adjusted mortality hazard ratio for NFL players relative to replacements was 1.38 (95% CI, 0.95 to 1.99; P = .09). Among career NFL players, the most common causes of death were cardiometabolic disease (n = 51; 35.4%), transportation injuries (n = 20; 13.9%), unintentional injuries (n = 15; 10.4%), and neoplasms (n = 15; 10.4%). Among NFL replacement players, the leading causes of death were cardiometabolic diseases (n = 19; 51.4%), self-harm and interpersonal violence (n = 5; 13.5%), and neoplasms (n = 4; 10.8%).

ところが、要約には記されていない死因が、本文の結果の末尾だけに記されている。
There were 7 deaths (4.9%) from neurological causes in the career NFL player group and none in the NFL replacement player group. All 7 of these deaths were due to amyotrophic lateral sclerosis.

Discussionではこの結果については一言も触れられていない。しかし、さすがにeditorialでは避けられなかったと見える。
Long-term Mortality in NFL Professional Football Players No Significant Increase, but Questions Remain. JAMA. Published online February 1, 2018

There was, however, a notable numerical difference in neurodegenerative disorders, in that 7 deaths were categorized as neurodegenerative, and these occurred only in the long-term players. All of these 7 deaths were categorized as due to amyotrophic lateral sclerosis (ALS), a prevalence rate far higher than the 4.3 cases per 100 000 people in the general population (and that statistic is based on the oldest age group, >70 years).(MMWR Surveill Summ. 2016;65(8):1-12) The finding of excess ALS cases has been reported previously in studies of NFL players compared with the general population.(Neurology. 2012;79(19):1970-1974. Brain. 2005;128(pt 3):472-476) However, no dementia cases were reported as the cause of death in this 1982-1992 cohort despite concerns about chronic traumatic encephalopathy (CTE), which had not become a recognized issue in football until a little more than 10 years ago.6- 8 In addition, the oldest men in both cohorts would have been in their mid to late 50s when the data for this analysis were obtained.

年齢はもちろん、アメリカンフットボールの選手というキャリアも合わせたコホートで、明らかに違う因子はプロでの持続したキャリアの有無しかない。そこでプロ選手のコホートの方にだけALSが、それも、2933人中7人という高頻度で。それは一般市民での10万人中4.3人の55倍である。これを偶然の一致というには余りにも無理があろう。アメフトのALSリスクについては、もはや誰も否定し得ないデータが出てしまったと言わざるを得ない。さらにアメフト以外にもサッカーのように頭部への外傷を繰り返すスポーツでもALSのリスクが示唆されている。
→Trauma and amyotrophic lateral sclerosis: a european population-based case-control study from the EURALS consortium.

参考
映画 Concussion
サッカーとCTEリスク

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