In this study, we found that our 61 never-smoking female flight attendants who worked on commercial aircraft before the ban on cigarette smoking in flights had on average significantly decreased diffusing capacity, with 51% of them having diffusing capacity below the lower limit of the 95% prediction interval for their sex, age, and height. In addition, these same flight attendants had decreased maximal airflow at mid- and low-lung volumes as well as pulmonary function evidence of air trapping suggestive of airflow obstruction. Although these pulmonary function abnormalities are consistent with the presence of a mild degree of COPD, our cohort on average had a normal FEV1
to FVC ratio (only 8 out of 61 subjects had ratios less than 0.70) and thus does not meet the GOLD criteria for mild COPD (42
). Despite this, the pulmonary function of these pre-ban flight attendants, particularly their diffusing capacity, is abnormal.
Furthermore, we developed a questionnaire-based estimate of air cabin-related occupational SHS exposure for our cohort of flight attendants by determining the number of pre-smoking ban years they had worked on domestic and international flights. We found that on average our cohort of flight attendants had served 74.6 ± 20.7 % of their active duty time in the pre-smoking ban era, which reflects that they had experienced considerable occupational SHS exposure. We then examined but did not find any association between the years of pre-ban employment, our surrogate of SHS exposure, and adjusted diffusing capacity (data not shown). However, our relatively small sample size along with other confounding factors, such as healthy worker effect (i.e. those employed longer had higher diffusing capacity) and possible exposure misclassification, limit our ability to draw any conclusion from this lack of association.
Occupational exposure to tobacco smoke has been an important source of SHS exposure in adults (15
) and presents a substantial health risk to workers (11
). Indeed, abnormal lung function has been reported in men exposed to SHS at their workplace (48
). Masi estimated that a never-smoking young woman who worked in an SHS-contaminated office would have her diffusing capacity reduced by three units below the value observed if she worked in a smoke-free office environment (46
). Recently, Rizzi et al reported for the first time that current exposure to SHS in a cohort of healthy male adolescents was associated with decreased diffusing capacity; this lung function impairment was independent of exposure to maternal smoking during pregnancy, but it was dependent on the amount of exposure to SHS (50
Air cabin-related SHS exposure in particular presented a substantial occupational health risk for the flight attendants because their SHS exposure occurred within the relatively confined space of commercial aircraft, which resulted in high intensity SHS exposures. Studies based on urine and serum concentrations of cotinine, a biomarker of exposure to tobacco smoke, have shown that, during the pre-ban era, the flight attendants experienced 6 to 7 times the SHS exposure compared to airlines ground-based workers, and 14 times that of the average person (51
). In fact, the urinary cotinine levels in these flight attendants approached the levels that are observed in active cigarette smokers (52
). This is important especially as the environmental condition of the aircraft cabin, including extremely low humidity (mean humidity of 5%) (13
) and presence of air pollutants such as ozone (53
), may have a compounding influence on the effects of SHS on lungs (54
Recently, Ebbert et al reported an association between sinusitis, middle ear infection, and asthma symptoms and the hours of time spent in a smoky cabin among never-smoking pre-ban flight attendants (55
). Our study extends the Ebbert et al study by showing that the never-smoking pre-ban flight attendants who have a significant history of occupational SHS exposure have abnormal pulmonary function suggestive of long-term damage to their lungs as seen in COPD.
Our study is limited by several factors. First, the small sample size of the study limits its statistical power. Second, recruitment in our study was not based on a random selection of flight attendants who flew prior to the ban on smoking on commercial aircraft, and thus the study population may not be a representative sample of the larger population of pre-ban flight attendants. We offered a comprehensive cardiopulmonary exam to all of flight attendants as an integral part of the study, but did not offer any other form of financial reimbursement. Therefore, subjects who joined this study may have done so for reasons related to underlying health concerns (although asymptomatic based on their answers to our questionnaire), employment status (e.g., retired), or other reasons (e.g., ability to travel to the clinic).
The sixty-one subjects selected for the current study had no smoking history, no pulmonary disease, and no underlying health problems that could have affected their lung function. Subjects’ ages indicate that they were older on average (mean 59.2 years, range 47–79) than flight attendants who flew prior to the airline smoking ban, based on data available from larger studies (56
), although we did not find this to account for the decrease in their diffusing capacity levels. While the study population may not reflect a wider population of pre-ban women flight attendants, it does constitute a group of relatively healthy older flight attendants from the pre-ban era known to have no underlying respiratory disease and for whom objective measures of lung function could be obtained.
Third, our study could not fully control for factors, other than aircraft SHS (e.g. SHS in childhood, adulthood, or other cabin effects such as exposure to ozone, low atmospheric pressures, or low humidity), that may have contributed to the decrease in subjects’ diffusing capacity levels. We did inquire whether participants were ever exposed to SHS in childhood or in their adult years when not aboard aircraft. However, for these exposures, we did not develop a SHS exposure surrogate similar to the one that we used for quantification of the flight attendants airline exposure. As discussed above, studies have shown that the concentration of aircraft SHS exposure was particularly high and considerably more than most other sources of environmental or occupational SHS exposure (51
). In addition, while we were able to calculate the duration of aircraft SHS exposure with relative accuracy by determination of flight attendants’ dates of employment, we expected the calculation of non-airline related SHS exposure would be more subject to recall bias. In our analysis, however, we did investigate the potential impact of any non-airline SHS exposure that the flight attendants may have received. Our results indicated that the diffusing capacity was not significantly different between the subjects who reported any additional non-airline SHS exposure and those who reported no additional exposure. It is possible that subjects’ non-airline SHS exposure in these instances was negligible compared to the exposure they received aboard aircraft. Other studies have quantified the differences in SHS exposure from aircraft and other sources (51
), though we were not able to verify these differences with our data.
Given these limitations, our study represents an initial step toward improved understanding of the health effects of aircraft SHS exposure in otherwise healthy older flight attendants based on objective measures of pulmonary function.
In conclusion, we found that in our cohort of 61 never-smoking pre-ban flight attendants, single breath carbon monoxide diffusing capacity and maximal airflow at mid- and low-lung volumes were significantly decreased suggestive of long-term damage to the lungs of these flight attendants. The most likely factor contributing to the pulmonary function abnormalities in these never-smoking pre-ban flight attendants is their occupational exposure to SHS in commercial aircraft. Further studies of a larger number of pre-ban as well as post-smoking ban flight attendants and better assessment of their cabin-related exposure to SHS and other pollutants may help identify the causes of these abnormalities.