Exhaled Carbon Monoxide With Waterpipe Use in US StudentsExhaled Carbon Monoxide With Waterpipe Use in US StudentsResearch Letters

To the Editor: Waterpipe smoking (hookah, arghile, shisha) is an increasing trend within the global tobacco epidemic.¹ A study of freshmen at a US university estimated a 15% current use and a 13% past use of waterpipe.² Toxic constituents including nicotine, carbon monoxide (CO), tar, and heavy metals remain after the smoke passes through water before inhalation by the smoker, with potentially increased risk of malignancy, impaired lung function, and cardiovascular disease.¹ The use of charcoal as a heat source and the large volumes of smoke produced during waterpipe use also raise health concerns. The World Health Organization has called for studying the health effects of waterpipe smoking.³ We therefore investigated concentrations of exhaled CO among a group of US university students who are waterpipe smokers.

Thirty-two participants were recruited from student organizations associated with waterpipe smoking; they were required to be healthy, familiar with waterpipe smoking (smoking participants, at least 1 waterpipe use per month; passively exposed participants, previous exposure to waterpipe), and not pregnant. All participants provided written informed consent and completed a baseline questionnaire. The study was approved by the institutional review board of the University of California, Berkeley.

Participants abstained from waterpipe smoking for 84 hours prior to the 60-minute smoking session, which was conducted on 3 evenings in April 2006 in a 103-m³ room of a private residence hall. Participants smoked according to their own custom. Three single-hosed waterpipes were shared by 10, 10, and 7 participants in the first, second, and third sessions, respectively. Five participants received passive exposure only.

Each waterpipe was cleaned, the base was supplied with fresh water, then the bowl was filled with 10 g of Al Fakher mu’assal tobacco (Alfakher Tobacco Trading, Ajman, United Arab Emirates) and covered with perforated aluminum foil. Participants added non–quick-lighting charcoal (Nour, Karabetian Import and Export Co, Los Angeles, California) throughout the session; approximately 30 g of charcoal was used with each waterpipe.

For each participant, exhaled CO concentration was measured immediately before and immediately after the smoking session in a separate room (ambient CO, 1-3 parts per million [ppm]) using the Micro CO Smoke Check monitor (Micro Medical Ltd, Kent, United Kingdom). The CO concentration in the session room was recorded using 3 HOBO CO Data Loggers (Onset Computer Corp, Bourne, Massachusetts) positioned throughout the room. Data from the monitors were averaged for each session.

The calculated sample size predicted an 80% power to detect a difference of 11 ppm in exhaled CO after 1 hour of waterpipe smoking (the primary outcome) using a 1-sided α of .05. The Wilcoxon signed rank test was used to test all associations except with session, for which the Kruskal-Wallis was applied. Analyses were performed using R version 2.3.1 (R Foundation for Statistical Computing, Vienna, Austria).

Participant characteristics are shown in Table 1. The medians (interquartile ranges) for the baseline, postsession, and difference in concentration of exhaled CO were 4.5 (3.5-5.2) ppm, 38 (23-56) ppm, and 32 (18-51) ppm, respectively (P < .001; Table 2) There were no statistically significant differences in change of exhaled CO concentrations by sex, smoking status, or session categories (Table 2). There was no significant change in exhaled CO among passive participants (P = .17).

The indoor CO concentrations reached a maximum (mean) concentration of 40 (26) ppm, 37 (25) ppm, and 31 (18) ppm during the 3 sessions. The CO values in the 3 room locations were similar, indicating well-mixed air.

Except for the primary outcome, analyses were exploratory and may be underpowered. Although no significant differences in increased exhaled CO were found between cigarette smokers and nonsmokers, these participants smoked relatively few cigarettes (only 1 smoked more than 3 cigarettes per day).

Despite these limitations, our observations suggest that the exhaled CO of waterpipe smokers after the session (mean, 42 ppm) was greater than the amount reported in 1 pack-per-day cigarette smokers (mean, 17 ppm),⁴ and the increase in exhaled CO was greater than that reported in waterpipe smokers in Jordan (mean, 14 ppm)⁵ and Lebanon (mean, 22 ppm).⁶ Indoor CO levels generally increased throughout the session, and longer sessions may exceed United States Environmental Protection Agency air standards (35 ppm averaged over 1 hour).⁷ Despite a perception of reduced harm held by some students who are waterpipe smokers,² the high levels of exhaled CO found in this study indicate a possibly significant health hazard from use of waterpipes that requires further study.