Table 4.
Model-based estimated annual decline in FEF 25–75 (mL/second/year) by treatment group in the full sample, and stratified by cigarette smoking status (Additional file 1 : Tables S3 and S4 for model coefficients)
| Full sample | Stratified by smoking status | |||||
|---|---|---|---|---|---|---|
| All treatment groups: | Unadjusted | Adjusted (model-based) | P value a | Never smokers | Former smokers | Current smokers |
| Mean (SD) † | Mean (95% CI) †† | Mean (95% CI) †† | Mean (95% CI) †† | Mean (95% CI) †† | ||
| Placebo | −63 (191) | −61 (−78, −43) | reference | −44 (−73, −15) | −58 (−82, −32) | −106 (−148, −63) |
| Vitamin E | −45 (201) | −46 (−66, −29) | 0.2739 | −47 (−76, −18) | −42 (−67, −17) | −59 (−95, −21) |
| Selenium | −67 (200) | −64 (−81, −47) | 0.6620 | −67 (−95, −38) | −75 (−100, −49) | −45 (−85, −5)* |
| Vitamin E and Selenium | −45 (190) | −47 (−64, −29) | 0.2719 | −71 (−102, −40) | −30 (−55, −5) | −50 (−90, −10)* |
| Marginal Models b : | ||||||
| Any Selenium versus Placebo | Placebo | −61 (−78, −43) | reference | −44 (−73, −15) | −57 (−82, −32) | −106 (−148, −63) |
| Any Selenium | −56 (−69, −44) | 0.7020 | −68 (−90, −47) | −52 (−70, −34) | −47 (−76, −19)* | |
| Any Vitamin E versus Placebo | Placebo | −61 (−78, −43) | reference | −44 (−73, −15) | −57 (−82, −32) | −105 (−147, −63) |
| Any Vitamin E | −46 (−58, −34) | 0.2058 | −59 (−80, −38) | −36 (−54, −18) | −54 (−81, −27)* | |
Abbreviations: FEF 25–75 forced expiratory flow rate from the 25th to 75th percentile of the forced vital capacity, mL milliliter.
*P < 0.05; more specifically, in current smokers selenium vs. placebo P = 0.0219, vitamin E + selenium vs. placebo P = 0.0236, any selenium vs. placebo P = 0.0095, any vitamin E vs. placebo P = 0.0352, only vitamin E vs. placebo P = 0.1553; all other smoking-stratified treatment vs. placebo comparisons are P > 0.05.
†Mean decline, mL/seconds/year (SD); calculated for men with ≥2 years between first and last pulmonary function tests where date of last test ≤ March 1, 2009; calculated in 418 (placebo), 426 (vitamin E), 416 (selenium) and 417 (vitamin E + selenium) participants.
††Model-based estimated mean decline, mL/second/year and 95% confidence interval; main effects models adjusted age, height, race, smoking status, time and tested time x treatment effect (effect of treatment on slope); smoking interaction models adjusted age, height, race, smoking status, and all two way interactions and tested smoking x time x treatment interaction (effect of treatment on slope within smoking group).
aP value from mixed-effects linear regression model, with placebo reference group.
bMarginal models combine treatment groups. Any selenium model compares participants on any selenium (selenium alone and in combination with E) to placebo. In a separate model, participants on any vitamin E (vitamin E alone and in combination with selenium) are compared to placebo.