Differential effects of tobacco cigarettes and electronic cigarettes on endothelial function in healthy young people

Abstract

Tobacco cigarette (TC) smoking has never been lower in the United States, but electronic cigarette (EC) vaping has reached epidemic proportions among our youth. Endothelial dysfunction, as measured by flow-mediated vasodilation (FMD) is a predictor of future atherosclerosis and adverse cardiovascular events and is impaired in young TC smokers, but whether FMD is also reduced in young EC vapers is uncertain. The aim of this study in otherwise healthy young people was to compare the effects of acute and chronic tobacco cigarette (TC) smoking and electronic cigarette (EC) vaping on FMD. FMD was compared in 47 nonsmokers (NS), 49 chronic EC vapers, and 40 chronic TC smokers at baseline and then after EC vapers (n = 31) and nonsmokers (n = 47) acutely used an EC with nicotine (ECN), EC without nicotine (EC0), and nicotine inhaler (NI) at ~4-wk intervals and after TC smokers (n = 33) acutely smoked a TC, compared with sham control. Mean age (NS, 26.3 ± 5.2 vs. EC, 27.4 ± 5.45 vs. TC, 27.1 ± 5.51 yr, P = 0.53) was similar among the groups, but there were more female nonsmokers. Baseline FMD was not different among the groups (NS, 7.7 ± 4.5 vs. EC:6.6 ± 3.6 vs. TC, 7.9 ± 3.7%∆, P = 0.35), even when compared by group and sex. Acute TC smoking versus control impaired FMD (FMD pre-/postsmoking, -2.52 ± 0.92 vs. 0.65 ± 0.93%∆, P = 0.02). Although the increase in plasma nicotine was similar after EC vapers used the ECN versus TC smokers smoked the TC (5.75 ± 0.74 vs. 5.88 ± 0.69 ng/mL, P = 0.47), acute EC vaping did not impair FMD. In otherwise healthy young people who regularly smoke TCs or ECs, impaired FMD compared with that in nonsmokers was not present at baseline. However, FMD was significantly impaired after smoking one TC, but not after vaping an equivalent "dose" (estimated by change in plasma nicotine) of an EC, consistent with the notion that non-nicotine constituents in TC smoke mediate the impairment. Although it is reassuring that acute EC vaping did not acutely impair FMD, it would be dangerous and premature to conclude that ECs do not lead to atherosclerosis.NEW & NOTEWORTHY In our study of otherwise healthy young people, baseline flow-mediated dilation (FMD), a predictor of atherosclerosis and increased cardiovascular risk, was not different among tobacco cigarette (TC) smokers or electronic cigarette (EC) vapers who had refrained from smoking, compared with nonsmokers. However, acutely smoking one TC impaired FMD in smokers, whereas vaping a similar EC "dose" (as estimated by change in plasma nicotine levels) did not. Finally, although it is reassuring that acute EC vaping did not acutely impair FMD, it would be premature and dangerous to conclude that ECs do not lead to atherosclerosis or increase cardiovascular risk.

Keywords: electronic cigarettes; endothelial function; flow-mediated dilation; nicotine; tobacco cigarettes.

Conflict of interest statement

No conflicts of interest, financial or otherwise, are declared by the authors.

Figures

Fig. 1.

Baseline flow-mediated dilation (FMD) in the 3 groups. Among the 3 groups, including nonsmokers (n = 47), chronic electronic cigarette (EC) vapers (n = 49), and chronic tobacco cigarette (TC) smokers (n = 40), baseline FMD was not different unadjusted or adjusted for artery diameter, whether reported as percent change (%∆; A), absolute change (mm∆; B), or normalized for shear stress [arbitrary units ∆ (AU∆); C]. Unadjusted means compared between groups using a repeated-measure (mixed) analysis of variance model and displayed as mean (25–75%) with whiskers to minimum to maximum of the data.

Fig. 2.

Changes in plasma nicotine. The increase in plasma nicotine levels was not different in chronic tobacco cigarette (TC) smokers (n = 31) after smoking 1 TC and in chronic electronic cigarette (EC) vapers (n = 22) after using the EC with nicotine (ECN). When EC vapers used the ECN, the increase in nicotine was significantly greater compared with the nicotine inhaler (NI, n = 19). When nonsmokers used the ECN (n = 41), the increase in plasma nicotine was not different compared with the NI (n = 17). Mean postexposure minus baseline differences were compared across TC, ECN, and NI using a crossover repeated-measure (mixed) analysis of variance model, and results are displayed as means ± SE.

Fig. 3.

Change in flow-mediated dilation (FMD) in tobacco cigarette (TC) smokers after TC smoking. In TC smokers, FMD was significantly impaired pre-/postacute TC smoking (n = 31) compared with pre-/post-sham control (n = 32), whether reported as percent change (%∆; A), absolute change (mm∆; B), or normalized for shear stress [arbitrary units ∆ (AU∆); C]. Mean postexposure minus baseline differences were compared across TC and sham control using a t-tests and displayed as mean (25–75%) with whiskers to minimum to maximum of the data.

Fig. 4.

Change in flow-mediated dilation (FMD) in electronic cigarette (EC) vapers after EC vaping or nicotine inhaler (NI). In EC vapers, FMD was unchanged pre-/postacute use of an EC with nicotine (n = 22), EC without nicotine (n = 23), or NI (n = 19) compared with pre-/post-sham control (n = 31), whether reported as percent change (%∆; A), absolute change (mm∆; B), or normalized for shear stress [arbitrary units ∆ (AU∆); C]. Mean postexposure minus baseline differences were compared across electronic cigarette with nicotine (ECN), electronic cigarette without nicotine (EC0), NI, and sham control using a crossover repeated-measure (mixed) analysis of variance model and displayed as mean (25–75%) with whiskers to minimum to maximum of the data.

Fig. 5.

Change in flow-mediated dilation (FMD) in nonsmokers after electronic cigarette (EC) vaping or nicotine inhaler (NI). In nonsmokers, FMD was unchanged pre-/postacute use of an EC with nicotine (n = 41), EC without nicotine (n = 39), or NI (n = 17) compared with pre-/post-sham control (n = 44), whether reported as percent change (%∆; A), absolute change (mm∆; B), or normalized for shear stress [arbitrary units ∆ (AU∆); C]. Mean postexposure minus baseline differences were compared across electronic cigarette with nicotine (ECN), electronic cigarette without nicotine (EC0), NI, and sham control using a crossover repeated-measure (mixed) analysis of variance model and displayed as mean (25–75%) with whiskers to minimum to maximum of the data.