Smoking Cessation and Improvement in Mental Health Outcomes: Do People Who Quit Smoking by Switching to Electronic Cigarettes Experience Improvement in Mental Health?

Background

Strong evidence exists for mental health benefits of smoking cessation (i.e., reduction in symptoms and improvement in quality of life).^1,2 However, it is unclear whether this is true for those who quit smoking through switching to other tobacco alternatives such as electronic cigarettes (e-cigarettes, also known as vaping). This is a concern as e-cigarettes have been proposed as a safer alternative to conventional cigarettes, recommended for use in harm reduction programs and recommended as an effective method for smoking cessation. However, many e-cigarettes contain nicotine, which may have a negative effect on mental health. To further clarify this issue, this study examined depression status among former smokers, stratified by e-cigarette use in the Canadian household population.

Method

This study used the Public Use Microdata File from the Canadian Community Health Survey (CCHS) 2015–2016. The survey data were collected by Statistics Canada from a representative sample of the Canadian household population with an overall response rate of 59.5%.³ Survey respondents’ smoking status was classified as currently smoking (including both daily and occasional smokers), former smoker, and never smoker (i.e., never smoked a cigarette). E-cigarette use was identified based on self-report to the following item: “In the past 30 days, did you use an electronic cigarette, also known as an e-cigarette?” Survey respondents who had a score ≥10 on the Patient Health Questionnaire 9 were categorized as having a significant level of depressive symptoms.⁴

Analysis was based on estimated proportions and odds ratios (ORs), along with 95% confidence intervals (CI). The CCHS survey used stratified, multistage sample selection technique that included clustering and unequal selection probabilities. The design effect was accounted for in analysis using a set of 1,000 replicate bootstrap sampling weights that were provided by Statistics Canada for use with the datafile.

Results

The measurement of smoking was core content for provinces/territories in the CCHS 2015–2016, whereas the measurement of depression and e-cigarette status was optional. Nine provinces/territories chose to measure depression and four chose to measure e-cigarette, leading to n = 52,956 respondents having data on both depression and smoking status and n = 35,683 respondents having data on both depression, smoking, and e-cigarette status. Of 52,956 respondents with smoking and depression data, 17.6% were current smokers, 22.8% were former smokers, and 6.8% had elevated depressive symptoms. Of 35,683 respondents with complete data, 3.1% were e-cigarette users. As shown in the Table 1, 12.5% of respondents who were current smokers and 14.7% of respondents who were e-cigarette users had elevated depressive symptoms compared to only 5.8% among former smokers. Among former smokers using e-cigarettes, 16.1% had elevated depressive symptoms compared to 5.5% among former smokers who were not e-cigarette users. The ORs of elevated depressive symptoms were 2.9 times higher in current smokers (95% CI, 2.5 to 3.4) and 1.5 times higher for former smokers (95% CI, 1.2 to 1.7) compared to never smokers. However, the OR of elevated depressive symptoms for former smokers compared to never smokers differed by their e-cigarette use status: OR = 4.2, 95% CI, 2.5 to 7.1 if they were using e-cigarettes and OR = 1.4, 95% CI,1.2 to 1.7 if they were not using e-cigarettes.

Table 1.

Smoking Status and Depressive Symptoms^a in the Canadian Household Population.

Smoking Status	Depressive Symptoms % (95% CI)	Unadjusted OR (95% CI)	Adjusted ORb (95% CI)
Smokingc
Never smoking	5.49 (5.00 to 5.98)	Reference	Reference
Currently smoking	12.50 (11.28 to 13.73)	2.46 (2.12 to 2.84)	2.95 (2.53 to 3.44)
Former smoking	5.77 (5.10 to 6.43)	1.05 (0.90 to 1.23)	1.46 (1.23 to 1.72)
E-cigarette used
No	6.56 (6.07 to 7.05)	Reference	Reference
Yes	14.69 (11.18 to 18.20)	2.45 (1.83 to 3.28)	2.46 (1.82 to 3.33)
Former smokers by e-cigarette use status
E-cigarettes not usede	5.55 (4.88 to 6.20)	1.01 (0.86 to 1.18)	1.41 (1.19 to 1.68)
E-cigarettes usede	16.10 (9.14 to 23.06)	3.30 (1.97 to 5.53)	4.19 (2.47 to 7.11)

Note. PHQ-9 = Patient Health Questionnaire 9.

^aPHQ-9 score ≥ 10.

^b Adjusted for age and sex.

^c n = 52,956 respondents having data on both depression and smoking status were included for this analysis.

^d n = 35,683 respondents having data on both depression and e-cigarette status were included for this analysis.

^e Never smoking as reference group.

Discussion

To our knowledge, this is the first study to compare depression status among former smokers stratified by e-cigarette use in a representative sample of the Canadian household population. Overall, former smokers were less likely to have depression than current smokers; however, this did not apply if they used e-cigarettes. Former smokers using e-cigarettes were more likely to have depression than those who did not. These findings suggest that expected improvement in mental health status following smoking cessation^1,2 does not occur to the expected extent if cigarettes are replaced by e-cigarettes.

This study used cross-sectional data and thus cannot assess the temporal relationships between study variables. While nicotine may cause or perpetuate depressive symptoms, elevated depressive symptoms may also lead to self-medication with nicotine products. Mental health improves slowly and progressively with smoking cessation,² and e-cigarette users may be more recent quitters, which may explain their higher prevalence of elevated depressive symptoms. It is possible that the e-cigarette users were using them temporarily to get through the early stages of cessation, which may subsequently lead to long-term gains in mental health. Another limitation of the current study is that it is unclear whether the e-cigarettes contained nicotine, as the use of nicotine products in e-cigarettes was only legalized in 2018 in Canada. However, Health Canada reports that Canadians most often used e-cigarettes that contained nicotine during that time period.⁵ We were unable to find evidence of reduction in depressive symptoms after smoking cessation among those who report e-cigarette use, benefits that have been confirmed by systematic reviews,¹ and are evident in Canadian national survey data,² as previously reported. There is a need for longitudinal studies to clarify the risks and benefits of e-cigarette use, including those related to mental health, especially among people trying to quit smoking.