significant differences in the mean BC expo- sure assessed at baseline. Regression analysis. We found signifi- cant positive associations between sICAM-1 and BC averaged over the previous 4, 8, and 12 weeks (Table 2). Associations between aver- age BC for 4, 8, and 12 weeks and sVCAM-1 were in the same direction, with slightly smaller effect size, but were not statistically sig- nificant. As a sensitivity analysis, we also esti- mated the effects of BC exposure in weeks 5–8 and weeks 9–12 separately. For sICAM-1, the association with the longer BC lags were positive with effect size slightly smaller than the effect size for weeks 1–4 and not quite sta- tistically significant. A 0.30-gμ/m 3 increase in BC exposure during weeks 5–8 was associated with a 1.22% increase in sICAM-1 [95% con- fidence interval (CI), –0.10% to 3.00%], and during weeks 9–12, with a 1.09% increase in sICAM-1 (95% CI, –0.18% to 2.38%). For sVCAM-1, the estimated effects for the longer lags had the same effect size and direction as the effects for weeks 1–4 but were not statisti- cally significant (data not shown). Overall, we saw the same pattern of effects in the lagged 4-week intervals, with only slight weakening in effect when the lags were considered indi- vidually rather than cumulatively. Regression analysis and interactions. When we examined the effect of BC on sICAM-1 and sVCAM-1 by diabetes status, we saw effects only among diabetics, whereas nondiabetics showed no effect (Figure 2; interaction p-values < 0.05 for all models except 12-week BC and sVCAM-1). When we examined the effects of BC by statin use, interaction models suggested that effects were present only in participants who did not use statins, with little evidence of associa- tions among statin users (Figure 3; interaction p-values < 0.05 for sVCAM-1 only). In con- trast, we found no difference in the estimated effect of BC by obesity status on either out- come (data not shown). We restricted our sensitivity analysis of statin use interaction to participants who never used statins or always used statins Table 1. Characteristics of the NAS population at first visit. Covariate Mean ± SD or n (%) Age (years) 72.4 ± 7.0 BMI (kg/m2) 28.3 ± 4.2 Diabetes 126 (19.6) Obesity 180 (28.0) Statin use 242 (37.7) Smoking status Former smoker 657 (69.7) Current smoker 28 (2.9) Never smoker 258 (27.4) Pack-yearsa 30.4 (27.9) sICAM-1 (ng/mL) 295.4 ± 80.6 sVCAM-1 (ng/mL) 1058.9 ± 351.8 aFor current and former smokers. during the study period. The results were comparable, with the effect sizes estimated to be slightly larger in all categories in the restricted model, and statistically significant (data not shown). These differences could reflect some overall difference in health between statin users and nonusers because statin use was not randomized. Discussion We found that address-specific BC expo- sures averaged over 4, 8, and 12 weeks were Traffic particles and endothelial function positively associated with markers of inflam- mation and endothelial dysfunction in this elderly cohort. Exposure estimates based on our validated land-use regression model are more accurate than estimates based on ambient monitoring, which are often used for cohorts of this size. Our analyses suggest that diabetics are more susceptible to adverse effects of TRAP than are nondiabetics, but we found no evidence of effect modification by obesity. In addition, we observed a effect among participants who used statins Predicted BC (µg/m3) 0.03–0.18 0.18–0.24 0.24–0.29 0.29–0.35 0.35–0.42 0.42–0.48 0.48–0.56 0.56–0.64 0.64–0.87 0.87–2.5 Figure 1. Predicted average BC concentration in the Greater Boston area over a 4-week period. Table 2. Estimated percent increase in sICAM-1 and sVCAM-1 levels per 0.3-μg/m3 increase in BC, for 4-, 8-, and 12-week averages. Time period 4 weeks 8 weeks 12 weeks *p < 0.05. sICAM-1 Percent increase 1.50 1.58 1.49 95% CI 0.22 to 2.80* 0.18 to 3.00* 0.04 to 2.95* sVCAM-1 Percent increase 95% CI 1.00 –0.65 to 2.67 1.20 –0.58 to 3.02 1.26 –0.58 to 3.14 Environmental Health Perspectives • volume 119 | number 4 | April 2011 483