Private space second-hand smoke exposure and the mental health of non-smokers: A cross-sectional analysis of Canadian adults

Addictive Behaviors 38 (2013) 1679–1686

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Addictive Behaviors

Private space second-hand smoke exposure and the mental health of non-smokers: A cross-sectional analysis of Canadian adults Mark Asbridge a,⁎, Kristen Ralph a, Sherry Stewart a, b, c a b c

Department of Community Health and Epidemiology, Dalhousie University, 5790 University Avenue, Halifax, Nova Scotia, Canada B3H 1V7 Department of Psychiatry, Dalhousie University, 5909 Veteran's Memorial Lane, 8th Floor, Abby J. Lane Memorial Building, Halifax, Nova Scotia, Canada B3H 2E2 Department of Psychology, Dalhousie University, Life Sciences Centre, P.O. Box 15000, Halifax, Nova Scotia, Canada B3H 4R2

H I G H L I G H T S ► ► ► ►

We examine associations between SHS exposure and poor mental health in non-smokers. Exposure to SHS was measured in the respondents home and vehicle. SHS exposure was associated with anxiety, poor/fair mental health, and high stress. Associations were contextualized by gender, physical health, and smoking status.

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Keywords: Second-hand smoke Mental health Anxiety disorder Mood disorder Non-smokers

Introduction: The aim of this paper was to examine the association between exposure to second-hand smoke (SHS) among non-smokers, in the home and the vehicle, and poor mental health outcomes (mood disorder, anxiety disorder, poor/fair mental health, and high stress). Methods: Data were drawn from the 2010 Canadian Community Health Survey, a representative sample of 62,909 Canadians 12 years and older. Measures of SHS exposure are drawn from self-reported daily or near daily exposure in the home or in the vehicle. Mental health indicators include self-reported diagnosed mood and anxiety disorders, and self-report measures of overall mental health and experiences of stress. Associations between SHS exposure and poor mental health among non-smokers were examined in a series of logistic regression models. Additional analyses stratified on respondent's smoking status, physical health, and gender. Results: Analyses revealed that SHS exposure among non-smokers was associated with increased anxiety disorders, poor/fair mental health, and high stress, with no association to mood disorders. Stratified analyses demonstrated that associations between SHS and poor mental health are contextualized by respondent's gender, physical health, and smoking status. Conclusions: Beyond changes to physical health, SHS exposure in private spaces was negatively associated with the mental health of non-smokers. Public health efforts to reduce SHS exposure in private spaces are warranted. Findings also reveal additional targets for decreasing and eliminating the societal burden of mental health disorders. Further research is needed to examine causality and to explore associations between SHS exposure and specific mental health outcomes. © 2012 Elsevier Ltd. All rights reserved.

1. Introduction

Wagner, 1996; John, Meyer, Rumpf, & Hapke, 2004; Lyvers, Thorberg, Dobie, Huang, & Reginald, 2008; Pasco et al., 2008), anxiety disorders (Breslau & Klein, 1999; Breslau, Novak, & Kessler, 2004b; Cuijpers, Smit, ten Have, & de Graaf, 2007; Feldner, Babson, & Zvolensky, 2007; Isensee, Wittchen, Stein, Höfler, & Lieb, 2003; Lasser et al., 2000; Mykletun, Overland, Aarø, Liabø, & Stewart, 2008; Zvolensky, Feldner, Leen-Feldner, & McLeish, 2005), and stress-related disorders (Aronson, Almeida, Stawski, Klein, & Kozlowski, 2008; Lyvers et al., 2008; Morissette, Brown, Kamholz, & Gulliver, 2006; Parrott, 1999, 2004), though the mechanisms responsible for these associations are not always clear. Despite this work, little research has examined the impact of second-hand smoke (SHS) exposure on the mental health

In broadening our understanding of the underlying factors associated with poor mental health, the effects of smoking have emerged as an important area of research. This research has found strong associations between smoking and poor mental health outcomes. Smokers have been shown to be at an increased risk, relative to non-smokers, for major depressive disorder and other mood disorders (Boys et al., 2003; Breslau, Novak, & Kessler, 2004a; Brown, Lewinsohn, Seeley, & ⁎ Corresponding author. Tel.: +1 902 494 3761; fax: +1 902 494 1597. E-mail address: [email protected] (M. Asbridge). 0306-4603/$ – see front matter © 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.addbeh.2012.10.008

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of non-smokers. The aim of this paper is to examine the association of exposure to SHS, either in the home or vehicle, on the mental health of non-smokers. 1.1. Second-hand smoke: health effects and policy responses The U.S. National Institutes of Health defines SHS as the smoke emitted from the burning end of a cigarette, cigar, or pipe, along with a smoker's exhaled smoke (U.S. Department of Health and Human Services, 2004; United States Environmental Protection Agency, 1992), and has been shown to have a detrimental effect on everyone exposed (California Environmental Protection Agency, & Office of Environmental Health Hazard Assessment, 1997; Charney, Heninger, & Breier, 1984; Dome, Lazary, Kalapos, & Rihmer, 2010; Law et al., 2003; Matt et al., 2004; United States Department of Health and Human Services, 2006). Recognition of the negative effects of SHS exposure has resulted in the development of policies aimed at reducing exposure (Asbridge, 2004; United States Department of Health and Human Services, 1986), typically through restrictions on smoking in public spaces (Hopkins et al., 2001; Pierce, León, & IARC Working Group, & IARC Secretariat, 2008). Nonetheless, many people are still exposed to SHS in the home, vehicle, and other private and public locations (Leatherdale & Ahmed, 2009). In 2007, it was reported that 7.3% of Canadian children, 13% of Canadian teenagers, and 8.7% of all non-smokers were regularly exposed to SHS in the home, while 8.1% of non-smokers reported SHS exposure in vehicles (Iribarren, Friedman, Klatsky, & Eisner, 2001; Jefferis et al., 2009; Statistics Canada, 2007). SHS exposure in the home or vehicle is particularly detrimental due to the size of the space and the often larger quantity of cigarettes consumed in those environments, producing higher air nicotine concentrations (Jones, Navas-Acien, Yuan, & Breysse, 2009; Leech, Wilby, & McMullen, 1999; Ott, Klepeis, & Switzer, 2008; Rees & Connolly, 2006). This has been noted in studies showing a larger decrement in healthrelated quality of life per hour of SHS exposure in a home location and in vehicles compared to a public or workplace location (Bélanger et al., 2008; Bridevaux et al., 2007; Riboli et al., 1990). While some Canadian jurisdictions (Ontario, British Columbia, Nova Scotia, and the Yukon) have implemented restrictions on smoking within a vehicle in the presence of a passenger under the ages of 16 or 19 years, instituting bans on smoking in the home have been harder to achieve (Green, Courage, & Rushton, 2003).

intrasynaptic dopamine and a heightened release of dopamine due to smoking, which has also been linked to higher levels of depression (Bandiera et al., 2010); SHS exposure could similarly trigger this heightened release of dopamine in depression vulnerable individuals. There is, however, only a small amount of research conducted on the mental health effects of SHS exposure. A well-designed study using data from the Scottish Health Survey (Hamer, Stamatakis, & Batty, 2010), found that SHS exposure, measured through cotinine, was associated with higher levels of psychological distress and future psychiatry illness in healthy adult non-smokers. This effect was demonstrated only among those exposed to high levels of SHS (defined as cotinine levels between 0.71 and 14.99 ug/L). Other studies of specific subpopulations have also noted positive associations. Two studies of women exposed to SHS found that compared to non-exposed women, those exposed reported poorer social functioning and lower health-related quality of life (Bridevaux et al., 2007; Sobotova, Liu, Burakoff, Sevcikova, & Weitzman, 2009). Meanwhile, a study of workers in rural Tokyo found an increase in the risk of depressive symptoms in non-smokers exposed in the workplace (Nakata et al., 2008). Finally, a small study of 170 mothers and their children found an association between mother's smoking, child's SHS exposure, and future depression and anxiety (Gatzke-Kopp & Beauchaine, 2007). More research is required, however, looking at SHS exposure, both in the home and in the vehicle, and a broad set of mental health outcomes that include specific disorders as well as overall mental health and well-being. Moreover, observed associations in previous studies need to be replicated in other jurisdictions, and with studies that include large representative samples from the general population. The purpose of this study was to contribute to knowledge on the effects of SHS exposure on mental health outcomes. We evaluated the relationships between SHS exposure, either in the home or the vehicle, and four mental health outcomes: diagnosed mood and anxiety disorders, and self-reported high stress and overall general mental well-being. In addition to contributing to the broader literature on the health effects of SHS, documenting an association between SHS exposure and negative mental health outcomes has numerous public health implications, including identifying new targets that may be used to decrease the societal burden of mental health disorders and barriers to wellness, and enhancing current public health campaigns to target specific populations and to provide preventative care for those at high risk. 2. Methods

1.2. Second-hand smoke and mental health 2.1. Data and sample As noted above, the detrimental effects of smoking on the mental health of smokers are well documented. Mood disorders (i.e. major depressive disorder), anxiety disorders (i.e. panic disorder and phobias), and stress have a higher incidence in smokers compared to non-smokers and former smokers. Given the chemical similarity between inhaled tobacco smoke and SHS it is only natural to suggest that non-smokers may experience deleterious effects of SHS on mental health similar to the acute effects of smoking on mental health observed in current smokers (Foulds et al., 1997). The pathway(s) by which SHS may produce poor mental health are not entirely clear and likely varied. One possibility is that stress and poor mental health may arise as a consequence of the decreased physical functioning (e.g., reduced lung function) resulting from SHS exposure (Caldirola, Bellodi, Cammino, & Perna, 2004). The anxiogenic effect of nicotine consumption supports the concept of smoking as a risk factor for panic (Isensee et al., 2003; Srivastava, Russell, Feyerabend, Masterson, & Rhodes, 1991); SHS might be similarly anxiogenic. Other explanations point to genetics, where shared pathways link both poor mental health and a heighted sensitivity to the effects of smoking. For example, there is an observed genetic predisposition for some individuals to have lower levels of resting

This study used data collected for the 2010 Canadian Community Health Survey (CCHS) Public Use Micro-data File. The CCHS is a household survey conducted with a nationally represented sample of 62,909 Canadian adults (age 12 years and older). Excluded are those living on Indian reserves and on Crown lands, institutional residents, full-time members of the Canadian Forces, and residents of certain remote regions. The survey provides health information for 126 regions in ten provinces/territories and is conducted by Statistics Canada in partnership with Health Canada and the Canadian Institute for Health Information. The survey assesses health status, healthcare utilization, and health determinants in a Canadian context. The targeted sample was divided among the provinces according to the population size and number of health regions within the province. For each province, regions were divided into major urban centers, cities, and rural areas. The cities and rural areas were stratified on a geographical basis and then according to socio-economic characteristics. The final sample was then reached by using a systematic sampling of households using random digit dialing methods. Survey interviews were conducted using computer assisted interviewing (CAI) and lasted, on average, 30 min. The response rate was 71.5%.

M. Asbridge et al. / Addictive Behaviors 38 (2013) 1679–1686

Smoking status in the CCHS was divided into the following categories: smoker (daily smoker and occasional smokers combined), former smoker (former daily smokers and former occasional smokers combined), and never smoker. Given the focus on SHS exposure, we analyzed only non-smokers (n=49,701), which include former and never smokers. 2.2. Measures The main independent variable was SHS exposure. We focused on SHS exposure in two private locations — in the home and in the vehicle. Home SHS exposure was measured by the question “Including both household members and regular visitors, does anyone smoke inside your home, every day or almost every day?” Similarly, vehicle SHS exposure was assessed by the question “In the past month, were you exposed to SHS, every day or almost every day, in a car or other private vehicle?” The response categories for both questions included yes, no, not applicable, don't know, refusal, and not stated. These measures were dichotomized and a new variable was created to measure any SHS exposure from either location. Mental health is more than the absence of mental disorders. It is a state of well-being where the individual is capable of dealing with the stress of daily life, contributing to their community and society, and is perceptive of their own skills (World Health Organization, 2007). For this reason, multiple measures of mental health were used including mood disorders, anxiety disorders, stress, and general mental wellbeing. Mood disorders were assessed using the question, “Do you have a mood disorder such as depression, bipolar disorder, mania, or

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dysthymia?” Similarly, anxiety disorders were assessed using the question, “Do you have an anxiety disorder such as a phobia, obsessive– compulsive disorder, or a panic disorder?” The preface to both questions indicated that respondents should only report on “conditions diagnosed by a health professional and are expected to last or have already lasted 6 months or more.” Mood and anxiety disorders were treated as binary variables measuring the presence or absence of a disorder. The third measure of mental health was self-perceived stress. This variable was based on the question, “Thinking about the amount of stress in your life, would you say that most days are: (not at all stressful, not very stressful, a bit stressful, quite a bit stressful, or extremely stressful)?” Although there is limited information on the psychometric properties of the question used to evaluate self-reported stress, the resulting variable has been used in other studies as a measure of self-reported stress (Tang, Nabalamba, Graff, & Bernstein, 2008; Tempier et al., 2009; Vasiliadis, Tempier, Lesage, & Kates, 2009). Self-perceived stress was collapsed into two categories with not at all stressful, not very stressful and a bit stressful as the referent category and quite a bit stressful and extremely stressful as the category of interest. The final measure of mental health was self-rated mental health, based on the question, “In general, would you say your mental health is: (excellent, very good, good, fair, or poor)?” Similar to self-reported stress, there is limited information on the psychometric properties of the question used to assess self-rated mental health. Nonetheless, the resultant variable has appeared previously in research on selfreported mental health (Andersen et al., 2006; Sobotova et al.,

Table 1 Descriptive statistics of study sample (unweighted n and percent or mean). Variables

Mood disorder Anxiety disorder Poor or fair mental health High stress SHS exposure Female sex Age (years) Province Ontario Atlantic Quebec Prairies Alberta British Columbia Territories Immigrant Marital status Married Common-law Widow/sep/divorce Single/never married Low income No Yes Not reported Highest education University graduate Some post-secondary High school graduate Less than high school One or more children b 12 in home Own dwelling Smoking status Never smoker Former smoker Current smokers Any chronic disease

Total CCHS sample (n = 62909)

Non-smoker study sample (n = 49701)

Non-smokers exposed to SHS (n = 4792)

Non-smokers unexposed to SHS (n = 44909)

N

Percent or median

N

Percent or median

N

Percent or median

N

Percent or median

4715 3639 3735 12,490 7943 34,363 62,909

7.51 5.79 6.10 19.90 12.60 54.60 45–49 years

3018 2305 2461 9102 4792 27,892 49,701

6.08 4.65 5.07 18.40 9.64 56.10 45–49 years

307 290 273 976 – 2326 4792

6.41 6.06 5.83 20.40 – 48.5 15–17 years

2711 2015 2188 8126 – 25,566 44,909

6.00 4.50 4.90 18.10 – 56.9 60–64 years

21,526 7614 11,271 7105 6009 7751 1633 8848

34.2 12.1 17.9 11.3 9.5 12.3 2.6 14.1

17,379 5951 8720 5592 4624 6404 1031 7647

34.9 11.9 17.5 11.1 9.3 12.9 2.0 15.4

1541 657 1038 584 477 387 108 434

32.2 13.7 21.7 12.2 9.9 8.1 2.3 9.1

15,838 5294 7682 5008 4147 6017 923 7213

35.3 11.8 17.1 11.2 9.2 13.4 2.1 16.1

26,329 5249 12,653 18,678

41.8 8.3 20.1 29.7

22,397 3496 9682 14,153

45.0 6.9 19.5 28.5

1398 442 508 2444

29.2 9.2 10.6 51.0

20,999 3027 9174 11,709

46.8 6.7 20.4 26.1

32,721 15,937 14,251

52.1 25.3 22.6

25,723 11,883 12,095

51.6 23.9 24.3

1892 1447 1453

39.5 30.2 30.3

23,831 10,436 10,642

53.1 23.2 23.7

31,101 4538 9700 17,570 11,834 46,626

49.4 7.21 15.4 27.9 18.1 74.1

25,085 3348 7252 14,016 9307 38,538

50.5 6.7 14.6 28.2 18.7 77.5

1726 402 812 1852 876 3534

36.0 8.4 16.9 38.6 18.3 73.7

23,359 2946 6440 12,164 8431 35,004

52.0 6.6 14.3 27.1 18.8 77.9

24,701 25,000 13,208 14,244

39.7 22.6 21.0 22.6

24,701 25,000 – 11,215

49.7 50.3 – 22.5

2459 2333 – 1008

51.3 48.6 – 21.0

22,242 22,667 – 10,207

49.5 50.5 – 22.7

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2009; Tang et al., 2008; Tempier et al., 2009; Vasiliadis et al., 2009). General mental health status was collapsed into two categories with the outcomes of excellent, very good and good, as the referent category and fair and poor as the category of interest. Variables shown to be associated with SHS exposure and mental health in the literature were controlled for in the analyses. These variables included province (derived from postal code), sex, age (in years), low income (less than $15,000), marital status (married, common-law, widowed/separated/divorced, single/never married), education (highest level achieved), immigrant status (Canadian born), presence of at least one child under the age of 12 living in the household, ownership of the dwelling by a member of the household, and smoking-related chronic physical conditions (presence of a diagnosed condition including asthma, high blood pressure, chronic bronchitis, heart disease, and cancer). Descriptive statistics for all measures are in Table 1. 2.3. Analytic approach Analysis of the data was conducted in two steps. First, logistic regression models were run for each of the four mental health outcomes, exploring both unadjusted and adjusted associations between SHS exposure and mental health. Second, a series of stratified analyses were completed to explore the association between SHS exposure and mental health separately by smoking status, chronic disease status, and gender. All analyses were conducted utilizing the population weights provided with the CCHS data. As the public use micro-data file does not include bootstrapping information, the reported standard errors for the odds ratios produced by the logistic regression models do not fully account for the complex sample design. For this reason, standard errors were estimated using robust methods which accounted for unequal variance but did not account for correlated observations. All analyses

were conducted using Stata Version 10. This study was reviewed and approved by the Health Sciences Research Ethics Board at Dalhousie University. 3. Results As Table 1 notes, approximately 10% of Canadian non-smokers report being exposed to SHS every day or almost every data, either in the home or in a vehicle. The third and fourth columns from Table 1 provide an overview of non-smokers exposed and unexposed to SHS. Clear differences exist by exposure status. Relative to non-exposed, a higher proportion of SHS exposed non-smokers have an anxiety disorder, report poor/fair mental health, and report experiencing high stress. Exposed non-smokers are also more likely to be male, younger, reside in Quebec, non-immigrants, single, of low income, and have less than a high-school education. Table 2 presents logistic regression results of the association of SHS exposure on mood and anxiety disorders. In both the unadjusted (OR = 1.13; P = 0.24) and adjusted (OR = 1.13; p = 0.29) models, SHS exposure was not associated with the presence of a mood disorder. The factors most strongly associated with mood disorders were female gender (OR=1.59; pb 0.01) and having a pre-existing chronic health condition (OR=1.83; pb 0.01). Turning to anxiety disorders, in both the unadjusted (OR=1.40: pb 0.01) and adjusted (OR=1.27; pb 0.05) models, SHS exposure was positively associated with the presence of an anxiety disorder. Female gender (OR=1.67; pb 0.01) and having an existing chronic health condition (OR=1.71: pb 0.01), had a similar positive association with having an anxiety disorder. Table 3 outlines logistic regression results for self-reported poor/fair mental health and self-perceived high stress. SHS exposure was positively associated with self-reported poor/fair mental in the unadjusted model (OR=1.31; pb 0.01), but this association became non-significant after adjusting for other covariates (OR=1.26; p=0.06). The factors most

Table 2 Logistic regression models of mood and anxiety disorders on SHS exposure (referent: non-exposure) and covariates among Canadian non-smokers (Odds ratios and z-statistics). Variables

Unadjusted mood (n = 49625)

Adjusted mood (n = 49625)

Unadjusted anxiety (n = 49610)

Adjusted anxiety (n = 49610)

SHS exposure Female sex Age (years) Province Ontario (ref) Atlantic Quebec Prairies Alberta British Columbia Territories Immigrant Marital status Married (ref) Common-law Widow/sep/divorce Single/never married Low income No (ref) Yes Not reported Highest education University graduate (ref) Some post-secondary High school graduate Less than high school One or more children b12 in home Own dwelling Never smoker (vs. former) Any chronic disease Wald test

1.13 (1.18) 1.64 (7.07)⁎⁎ 1.05 (7.18)⁎⁎

1.13 (1.32) 1.59 (6.12)⁎⁎ 1.02 (1.91)

1.40 (3.04)⁎⁎ 1.69 (6.87)⁎⁎ 1.00 (1.24)

1.27 (1.98)⁎ 1.67 (6.16)⁎⁎ 1.00 (0.00)

1.00 1.08 (0.78) 0.70 (−3.38)⁎⁎ 0.92 (−0.62) 1.09 (0.86) 0.92 (−0.71) 1.08 (0.44) 0.70 (−3.96)⁎⁎

1.00 0.87 0.57 0.84 1.08 0.90 1.01 0.68

1.00 1.46 (3.92)⁎⁎ 1.30 (2.46)⁎⁎ 0.93 (−0.51) 0.98 (−0.09) 1.10 (0.98) 0.85 (−0.68) 0.50 (−6.06)⁎⁎

1.00 1.16 1.05 0.81 0.97 1.10 0.74 0.55

1.00 1.22 (1.47) 1.75 (6.67)⁎⁎ 0.92 (−0.98)

1.00 1.27 (1.61) 1.33 (3.06)⁎⁎ 1.13 (1.05)

1.00 1.55 (3.26)⁎⁎ 1.62 (4.82)⁎⁎ 1.27 (2.85)⁎⁎

1.00 1.33 (1.87) 1.19 (1.62) 1.17 (1.27)

1.00 1.57 (6.22)⁎⁎ 0.64 (−4.67)⁎⁎

1.00 1.52 (5.36)⁎⁎ 0.71 (−3.35)⁎⁎

1.00 1.69 (6.29)⁎⁎ 0.97 (−0.23)

1.00 1.42 (3.65)⁎⁎ 0.86 (−1.26)

1.00 0.86 (−1.92) 1.00 (0.03) 1.34 (2.29)⁎

1.00 1.18 (1.31) 0.89 (−1.17) 0.84 (−2.00)⁎ 0.97 (−0.30) 0.68 (−4.93)⁎⁎ 0.67 (−5.44)⁎⁎ 1.83 (8.21)⁎⁎ 424.6 p > 0.01

1.00 1.41 (2.48)⁎ 1.09 (0.85) 1.33 (3.26)⁎⁎

1.00 1.20 (1.31) 1.01 (0.12) 1.19 (1.59) 0.98 (−0.11) 0.74 (−3.75)⁎⁎ 0.77 (−3.16)⁎⁎ 1.71 (6.75)⁎⁎ 237.6 p = 0.00

⁎⁎ p b 0.01. ⁎ p b 0.05.

0.78 0.67 0.61 2.12

(−3.01)⁎⁎ (−5.48)⁎⁎ (−7.42)⁎⁎ (10.8)⁎⁎

(−1.29) (−5.13)⁎⁎ (−1.45) (0.77) (−0.93) (0.09) (−3.89)⁎⁎

0.82 0.68 0.74 1.88

(−2.00)⁎ (−4.86)⁎⁎ (−3.99)⁎⁎ (8.12)⁎⁎

(1.44) (0.46) (−1.42) (−0.26) (0.93) (−1.26) (−5.09)⁎⁎

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Table 3 Logistic regression models of poor/fair mental health and high stress on SHS exposure (referent: non-exposure) and covariates among Canadian non-smokers (Odds ratios and z-statistics). Variables

Unadjusted poor/fair mental health (n = 48510)

Adjusted poor/fair mental health (n = 48510)

Unadjusted high stress (n = 49494)

Adjusted high stress (n = 49494)

SHS exposure Female sex Age (years) Province Ontario (ref) Atlantic Quebec Prairies Alberta British Columbia Territories Immigrant Marital status Married (ref) Common-law Widow/sep/divorce Single/never married Low income No (ref) Yes Not reported Highest education University graduate (ref) Some post-secondary High school graduate Less than high school One or more children b12 in home Own dwelling Never smoker (vs. former) Any chronic disease Wald test

1.31 (2.33)⁎ 1.16 (1.88) 1.04 (4.96)⁎⁎

1.26 (1.86) 1.02 (0.23) 1.02 (1.90)

1.11 (1.54) 1.14 (3.21)⁎⁎ 0.98 (−3.10)⁎⁎

1.17 (2.22)⁎ 1.19 (4.02)⁎⁎ 0.95 (−5.57)⁎⁎

1.00 1.05 0.77 1.08 0.86 0.97 1.08 1.06

1.00 0.98 0.67 1.10 0.93 0.98 1.09 1.05

1.00 0.77 (−3.89)⁎⁎ 1.26 (4.16)⁎⁎ 0.78 ⁎ (−3.10)⁎⁎ 0.93 (−0.91) 0.99 (−0.13) 0.62 (−3.82)⁎⁎ 0.90 (−1.86)

1.00 0.72 1.18 0.76 0.87 0.98 0.56 0.89

(0.44) (−1.99)⁎ (0.63) (−1.18) (−0.19) (0.37) (0.55)

(−0.16) (−2.65)⁎⁎ (0.74) (−0.54) (−0.15) (0.41) (0.47)

(−4.46)⁎⁎ (2.85)⁎⁎ (−3.38)⁎⁎ (−1.68) (−0.18) (−4.42)⁎⁎ (−1.88)

1.00 1.09 (0.56) 2.03 (7.47)⁎⁎ 1.10 (1.00)

1.00 1.23 (1.25) 1.46 (3.58)⁎⁎ 1.06 (0.44)

1.00 1.55 (6.05)⁎⁎ 0.96 (−0.58) 0.83 (−3.64)⁎⁎

1.00 1.21 (2.41)⁎ 1.05 (0.76) 0.80 (−2.84)⁎⁎

1.00 2.01 (7.91)⁎⁎ 1.39 (3.16)⁎⁎

1.00 1.76 (5.42)⁎⁎ 1.27 (1.95)

1.00 0.77 (−4.73)⁎⁎ 0.63 (−8.89)⁎⁎

1.00 0.85 (−2.65)⁎⁎ 0.77 (−3.82)⁎⁎

1.00 1.29 1.22 1.63 0.67 0.49 0.84 2.05

1.00 1.10 (0.60) 1.04 (0.32) 1.27 (2.06)⁎ 0.83 (−1.40) 0.55 (−6.83)⁎⁎ 0.87 (−1.59) 1.75 (6.80)⁎⁎ 287.7; p = 0.00

1.00 0.84 (−2.14)⁎ 0.67 (−5.85)⁎⁎ 0.52 (−12.7)⁎⁎ 1.27 (5.00)⁎⁎

1.00 0.88 (−1.52) 0.71 (−4.82)⁎⁎ 0.59 (−8.27)⁎⁎ 1.13 (2.12)⁎ 0.93 (−1.39) 0.87 (−2.79)⁎⁎ 1.28 (4.73)⁎⁎ 418.2; p = 0.00

(1.59) (1.72) (5.40)⁎⁎ (−3.52)⁎⁎ (−8.60)⁎⁎ (−2.07)⁎ (8.92)⁎⁎

0.97 (−0.60) 0.83 (−4.16)⁎⁎ 1.17 (3.14)⁎⁎

⁎⁎ p b 0.01. ⁎ p b 0.05.

strongly associated with poor/fair mental health were dwelling ownership, which has a negative association (OR=0.55; pb 0.01), and having an existing chronic health condition (OR=1.75; pb 0.01). Conversely, SHS exposure was not associated with self-perceived high stress in the unadjusted model, but was positively associated with self-perceived high stress after adjusting for covariates (OR=1.17; pb 0.05). Having less than a high school education (OR = 0.59; p b 0.01) had a strong negative association with self-perceived high stress, while the presence of an existing chronic health condition (OR = 1.28; p b 0.01) was positively associated with high stress.

Table 4 Logistic regression models of mental health outcomes on SHS exposure (referent: non-exposure) among Canadian non-smokers, stratified by smoking status, gender, and chronic disease, and adjusting for other covariates (Odds ratios and z-statistics). Stratification variables

Mood disorder

Smoking status Former smokers 1.00 (0.05) Never smokers 1.36 (1.68)

Anxiety disorder

Poor/fair mental High stress health

0.98 (−0.07) 1.35 (1.93) 1.61 (2.50)⁎ 1.11 (0.52)

1.29 (2.68)⁎⁎ 1.02 (0.24)

Gender Female Male

1.34 (2.05)⁎ 1.47 (2.33)⁎ 0.92 (0.47) 1.02 (0.11)

1.34 (1.77) 1.18 (0.89)

1.18 (1.80) 1.14 (1.34)

Any chronic disease Yes No

1.39 (1.88) 1.08 (0.53)

1.07 (0.72) 1.33 (1.98)⁎

1.40 (2.55)⁎ 1.11 (1.38)

1.01 (0.05) 1.38 (2.20)⁎

Note: All stratified models adjust for remaining covariates (sex, age, province, immigrant, marital status, low income, highest education, one or more children b 12 in home, own dwelling, never smoker, and any chronic disease). ⁎⁎ p b 0.01. ⁎ p b 0.05.

To further contextualize the main effects of SHS exposure on mental health, Table 4 presents stratified analyses examining sub-populations of non-smokers based on smoking status, gender, and chronic disease. In terms of smoking status, SHS exposure was positively associated with having an anxiety disorder (OR = 1.61; p b 0.05) among never smokers, and with self-perceived high stress (OR = 1.29; p b 0.01) among former smokers. In terms of gender, SHS exposure was positively associated with mood disorders (OR=1.35; pb 0.05) and anxiety disorders (OR=1.47; pb 0.05) only for females. Finally, stratification on chronic disease status demonstrates that SHS exposure was positively associated with anxiety disorders (OR = 1.38; Pb 0.01) and poor/fair mental health (OR = 1.33; p b 0.05), but only for those without an existing chronic disease. 4. Discussion and conclusion Despite the positive health benefits resulting from existing smokefree legislation enacted in most high income countries, this legislation is primarily aimed at addressing exposure in public places, with limited attention aimed to protect non-smokers exposed to SHS in the home or in private vehicles. In Canada, nearly 1 in 10 non-smokers report daily or near daily exposure to SHS in their home or in a vehicle, suggesting that private spaces remain as key sources of health harm to non-smokers. We find that this exposure is not equally distributed across the Canadian population, with higher SHS exposure among non-smokers who are male, under the age of 20, non-immigrants, single/never married, of low income, and with less than high school education; these trends replicate those found elsewhere (Bolte, Fromme, & GME Study Group, 2009; Bridevaux et al., 2007; Pérez, 2004; Wang et al., 2009). While much work has focused on the physical health effects of SHS exposure, the current study looked to build on the limited body

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of research that has focused on the negative mental health effects of SHS exposure. Overall, we find that SHS exposure is associated with having anxiety disorders, feelings of high stress, and with poor self-reported overall mental health (in the unadjusted model), but not with mood disorders. Stratified analyses reveal that these associations are conditional: SHS exposure is associated with anxiety disorders for never smokers, smokers without a chronic health condition, and female smokers; SHS exposure is associated with high stress for former smokers; SHS exposure is associated with poor/fair mental health for those without a chronic health condition; and that SHS exposure is associated with mood disorders but only for females. How might we interpret these findings? Looking specifically at anxiety disorders, the biological plausibility of this association, as noted previously, has been well documented in studies of current smokers (Breslau & Klein, 1999; Breslau et al., 2004a, 2004b; Charney et al., 1984; Isensee et al., 2003; Johnson et al., 2000; Morissette et al., 2006; Mykletun et al., 2008; Zvolensky et al., 2005), and thus exposure to SHS may produce similar mental health effects. It is also possible that the explanation for the link between SHS exposure and anxiety disorders differs from that observed among current smokers. For example, given that the association exists only for never smokers, and not for former smokers, it may be the loss of control experienced by those exposed to SHS, against their will, which contributes to the development of pathological anxiety reactions, rather than a direct physiologic response (Barlow, 2000). The lack of an association for former smokers may reflect the general imprecision of our anxiety measure. We found that non-smokers exposed to SHS were more likely to report high stress. This is consistent with the research which links SHS exposure to heightened sensitivities to stress and distress (Hamer et al., 2010; Iñiguez et al., 2009). Though the exact mechanism of this association is still unknown, it is possible that the effects of nicotine mimic the physiological effects of stress, thereby stimulating a stress response (Aronson et al., 2008; Lyvers et al., 2008; Morissette et al., 2006; Parrott, 1999, 2004). It is possible that the physiological effects of nicotine in SHS leads to increased heart rate, blood pressure, and breathing rate which may be perceived as increased stress (Srivastava et al., 1991). At the same time, stratified analyses show that this association exists only for former smokers rather than never smokers, which points to smoking history, and the relevant cues produced by consistent SHS exposure that may reintroduce feelings of stress. Additionally, it may be that former smokers may have poorer, unmeasured physical health due to their smoking history which, in turn, explains their elevated perceived stress. Or it may be that the associations between SHS exposure and stress, and anxiety, are spurious and due to some other common cause (Fergusson, Goodwin, & Horwood, 2003). The expected relationship between SHS exposure and mood disorders was only observed in females. The absence of a universal relationship is inconsistent with studies in the literature which have found a strong link between SHS exposure and depression (Nakata et al., 2008; Petty, 1995; Pomerleau, Pomerleau, Namenek, & Marks, 1999; Yolton et al., 2008). Depression is the mood disorder that has been most studied in relation to its association with SHS exposure, while other mood disorders, such as bipolar disorder, have not been as extensively studied. Current findings may be due to the use of the broad category of mood disorders as opposed to assessing the relationship between SHS exposure and the individual mood disorders. For example, if no association exists between bipolar disorder and SHS exposure, our broad measure may bias the results of the association between SHS exposure and mood disorders towards the null. Finally, we find that the association between SHS exposure and self-reported general mental health is contextualized by chronic disease status, such that only for those without a chronic physical condition was SHS exposure associated with poor/fair mental health. This finding reminds us that there is more to the negative health effects of SHS than simply deficits in physical health, such that we must expand our focus on health outcomes of SHS exposure to include mental health.

There were a number of limitations to this study. First, all data was based on self-report and may have been influenced by recall bias. However, previous research on the validity of self-reports of SHS exposure shows that levels of nicotine biomarker concentrations were typically consistent with self-reported SHS exposure, and, at times, exposure was under-reported and the actual exposure prevalence was higher than reported (Patten & Williams, 2007). Second, the cross-sectional design of the survey does not allow for an analysis of the causal nature of the relationship. For this reason, we cannot account for the direction of the relationship between SHS exposure and mental health. It may be that non-smokers who have a mental illness or poor mental health are more likely to be exposed to SHS. Third, we cannot rule out potential confounding due to unmeasured variables, such as home environment or intensity of SHS exposure. Fourth, as the CCHS survey contains more screening questions than diagnostic questions, the relationship between SHS exposure and mental health was analyzed for a broad range of mental health outcomes. Mood and anxiety disorders were screened using a single item self-report measure and thus potential problems regarding validity may arise. Although respondents were reminded to only confirm disorders that had been diagnosed by a health professional, it is possible that actual diagnoses may not match with the information provided by the respondents. Information on the reliability of respondent's self-reported diagnoses screened using a single item was not available, although the CCHS data has been used in additional studies of mental health outcomes utilizing the same measures (Tempier et al., 2009). Finally, the severity of mental disorders was not measured in the survey and thus potential gradients of associations based on disorder severity could not be estimated. In conclusion, the findings of this study need to be interpreted with caution. Further studies are required to better understand the underlying mechanism of action of SHS exposure on the mental health of non-smokers. Regardless of the specific mechanisms by which negative mental health outcomes are associated with SHS exposure, it is certain that this information may have useful implications for public health policy. A further reduction in the exposure of non-smokers to SHS, particularly in private spaces, may help alleviate some of the mental health burden. Although the public health implications of a decrease in exposure to SHS are positive, it remains that one in ten non-smokers were regularly exposed to SHS, a number that is still much too high. As was shown by the information included in this study, interventions that target SHS exposure in the home and vehicle may be beneficial for non-smokers' mental health as well as their physical health; such restrictions can be top-down and policy driven or, equally advantageous, self-imposed. Role of funding sources This research was supported by a Small Project Grant from the Ontario Tobacco Research Unit. OTRU had no role in the study design, collection, analysis or interpretation of the data, writing the manuscript or the decision to submit the paper for publication. Contributors All authors have made substantial contributions to the conceptualization, design, analysis and interpretation of the data and to the drafting and revising of the manuscript. Conflict of interest None. Acknowledgments None.

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