Association between years of American football play and PLP concentrations. (A) Distribution of years of American football play by PLP concentrations dichotomized into high and low based on the sample median split. The bar is the mean and the error bars are 95% CI. The figure shows unadjusted associations. Analysis of covariance controlling for age, education level, arteriolosclerosis and CTE stage showed the difference to be significant (F = 6.90, mean diff. = 1.79, 95% CI = 0.45–3.13, P = 0.01). (B) Scatter plot of the association between years of American football play and PLP as a continuous variable. The figure shows unadjusted associations. Multivariable linear regression models showed that more years of football play was associated with lower PLP concentrations (unstandardized beta = −2.45, 95% CI = −4.52, −0.38, t = −2.34, P = 0.02), adjusting for age at death, level of education, arteriolosclerosis and CTE stage.