Highly-elevated γ-tocopherol associates with reduced FEV
and FVC at ages 21–55. We a priori defined γ-tocopherol groups to model the average Western European/Asian γ-tocopherol levels (1–2 μM) (Additional file 2: Table S2)  and to model the average U.S.A. γ-tocopherol levels (3–4.8 μM and 4.9-10 μM) (Table 2 and Additional file 2: Table S2) [1–4]. We also defined a priori a γ-tocopherol group as >10 μM to model the 5-fold higher γ-tocopherol observed in our animal studies . In study year 5, the four γ-tocopherol categories represented from lowest to highest γ-tocopherol groups of CARDIA: 36 (1.1%), 1291 (38.0%), 2015 (59.3%), and 58 (1.7%) participants. To examine the association of γ-tocopherol with FEV1, FVC and FEV1/FVC as a function of participant age, we used generalized estimating equations (GEE) to analyze spirometry and tocopherol as described in the Methods and Additional file 3: Methods. For GEE models, included were the following variables: center, race, exam year, height, height2, sex, BMI, smoking status, asthma group, average α-tocopherol concentration, 3 dummy variables representing the 4 γ-tocopherol groups, and the interactions of the four γ-tocopherol groups with age. The number of readings used for analysis for low, moderate, moderate-high, and highly-elevated γ-tocopherol groups were: (A, D, G) 93, 3493, 5381 and 160, respectively, for all participants; (B, E, H) 80, 2696, 4281, and 123, respectively, for non-asthmatics; and (C, F, I) 13, 797, 1100 and 37, respectively, for self-reported ever asthmatics. A missing data point in C, F and I at age 21–27 in the low γ-tocopherol group occurred because the participants at this age did not have this level of γ-tocopherol in the self-reported asthmatics. Nevertheless, for the self-reported asthmatics, the high γ-tocopherol group at age 21–27 was significantly different than the groups with moderate levels of γ-tocopherol. *, p < 0.05 compared to the other groups at 21–27 years old.