Studies have shown that the effectiveness of mucociliary clearance is impaired in smokers compared to nonsmokers.1,2 It is also known that, in nonsmokers, regular physical activity when performed at moderate intensity improves the immune system response.3 However, the relationship between physical activity and mucociliary transport is not completely clear and has shown conflicting results. Wolff et al.4 observed a slight increase in mucociliary clearance after exercise, unlike Olseni and Wollmer5 who observed no substantial changes. Furthermore, these studies only described the acute (i.e., transient) response of the mucociliary system to exercise, but the chronic adaptive response to regular daily physical activity remains unknown. In addition, these studies were performed only in nonsmokers, and to the authors’ best knowledge, no studies involving this issue had yet been carried out in smokers.

Thus, the aim of this study was to describe the relationship between mucociliary transport and the level of physical activity in daily life (PADL) in healthy smokers (i.e., with no lung function impairment) and healthy nonsmokers.

Eighty-two subjects entered the study (52 smokers and 30 nonsmokers), and none of them were excluded during the assessments. Results are shown in Table 1. All three groups of smokers had higher COexh than the nonsmokers group (p<0.05 for all). There was no difference in the number of steps/day between any of the groups (p>0.05 for all). According to the number of steps/day, there was a wide range of subjects with different activity levels, although in general, all groups could be classified as somewhat active to physically active (Table 1).

The median (confidence interval) of STT in light smokers showed no significant reduction in the mucociliary transport compared to nonsmokers (9 [7–11]min and 8 [8–11]min, respectively; p=0.08). Both moderate and heavy smokers had significantly higher STT values than nonsmokers (13 [11–17]min; p=0.04 and 13 [10–21]min; p=0.04, respectively) and light smokers (p=0.02 for both).

In the general group of smokers, no significant correlation occurred between STT and steps/day (r=−0.04; p=0.78). There was a negative significant correlation between STT and steps/day only in light smokers (r=−0.55; p=0.02) and in nonsmokers (r=−0.42; p=0.02) (Fig. 1). No such significant correlation was found in the groups of moderate (r=0.31; p=0.15) and heavy smokers (r=−0.36, p=0.23).

Figure 1.

Correlation between saccharin transit time (STT) and physical activity in daily life (PADL, in steps per day) in (A) light smokers and (B) nonsmokers.

(0.1MB).

Furthermore, in the general group of smokers, there was no significant correlation between STT and pack/years index (r=−0.14; p=0.30), years of smoking (r=−0.13; p=0.37) and age (r=−0.23; p=0.09). Similarly, number of steps/day was not correlated to pack/years index (r=0.01; p=0.92), years of smoking (r=−0.18; p=0.22) and age (r=−0.03; p=0.81).

The power of the study was calculated by comparing the difference between two correlations, i.e., STT versus steps/day in the control group (0.42) and in the general group of smokers (0.04). By using an α=0.05 (double-sided) and a power of 80%, a total of 52 subjects provided a power of 0.82 in order to detect this difference.

This study showed that, specifically in smokers with light cigarette consumption and non-smokers, PADL is modestly but significantly associated with mucociliary function, unlike for smokers with moderate to severe cigarette consumption. Such results can be linked to the fact that there was no impairment in mucociliary transport in light smokers, while those with moderate to severe consumption showed impaired clearance. However, caution is required to avoid the interpretation of these results as describing a causative relationship between physical activity and mucociliary function, since the results are based solely on simple correlations.

Mucociliary transport (MCT) is the main defense mechanism of upper and lower airways15,16 and may be influenced by different conditions such as in response to stress, physical exercise and exposure to noxious particles (e.g., cigarette smoke).17 Physical exercise is, in general, classified as a stressful stimulus,18 but the MCT response to exercise can be divided into acute (i.e., transient) and chronic adaptation.19 The acute response to exercise is associated with increased levels of adrenergic mediators,20 which stimulate the ciliary beat frequency21,22 and thus the airways clearance. Some studies23–25 have confirmed this idea and found that the respiratory mucosa function is significantly altered by exercise, with improved activity during light-moderate exercise, and impaired activity after strenuous exercise. The novel feature of our study, however, was to investigate how the MCT behaves in relation to the regular level of physical activity (i.e., its chronic adaptation). In our view, the fact that the MCT in light smokers behaves similar to nonsmokers might underline the benefits of regular physical activity for the respiratory system in light smokers. However, in those who already have impairment in STT (i.e., moderate and heavy smokers), the mucociliary system is slowed down by the intensity of tobacco consumption regardless of the level of physical activity. Therefore, in these subjects, regular physical activity is not linked to MCT, but a substantial reduction in smoking intensity is required. On the other hand, as previously mentioned, the design of the present study does not provide solid proof of a causative relationship between higher PADL and better MCT.

The similarities between the results of light smokers and nonsmokers might be due to the degree of daily exposure to cigarette smoke for the former, which was possibly not intense enough to cause important structural damage and reduce mucociliary transport, as happened with moderate and heavy smokers. Since for the general group of smokers STT was not correlated to PADL level, age, pack/years and years of smoking, it is hypothesized that the MCT in smokers depends more on the current daily cigarette consumption than on smoking history and physical activity level. This hypothesis is in line with what was previously suggested by Stanley et al.,2 although that study did not include a detailed profile of the smoking habits (which the present study does) and did not include regular physical activity as one of its outcomes.

The sample size of this present study is relatively small, particularly after stratification according to daily cigarette consumption. This reduces further sub-analysis and could be considered as a limitation of the study. However, despite the relatively small sample in each group, this stratification was important since it provided relevant results such as the differences between light smokers versus moderate/heavy smokers. Further studies with larger number of smokers with different intensities of cigarette consumption would be welcome. Moreover, the authors used minutes to express saccharin transit time for reasons of clarity, although the specialized literature occasionally reports it in seconds.

In conclusion, specifically in light smokers and non-smokers, better mucociliary function is associated to higher daily physical activity level, as opposed to the decreased mucociliary function observed in smokers i.e., those with moderate and heavy cigarette consumption.

This work was supported by the Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), Brazil.

The authors have no conflicts of interest to declare.