Relationship Between Secondhand Smoke Exposure and Depressive Symptoms: A Systematic Review and Dose⁻Response Meta-Analysis

Commercial determinants of mental ill health: An umbrella review

Mental ill health has complex and interrelated underlying causes, with wider determinants of health often overlooked as risk factors. The 'commercial determinants of health' are gradually receiving more attention and recognition but there is a relative lack of awareness of the commercial determinants of mental health. This aim of this umbrella review was to synthesise systematic review level evidence for the association between commercial determinants and mental health outcomes. This umbrella review included evidence from high, middle, and low-income countries. We included terms related to broader commercial activities and terms focused on six key unhealthy commodities (tobacco, alcohol, ultra-processed foods, gambling, social media, fossil fuels) and the impacts of fossil fuel consumption (climate change, air pollution, wider pollution). We included 65 reviews and found evidence from high quality reviews for associations between alcohol, tobacco, gambling, social media, ultra-processed foods and air pollution and depression; alcohol, tobacco, gambling, social media, climate change and air pollution with suicide; climate change and air pollution with anxiety; and social media with self-harm. There was a lack of evidence examining wider practices of commercial industries. Our umbrella review demonstrates that by broadening the focus on commercial determinants, the influence of commercial products and activities on mental ill health can be better understood. The lack of research examining broader commercial practices on mental ill health is an area that should be addressed. Our review highlights the existing base of high-quality evidence for many of these unhealthy commodities' impacts on mental ill health and indicates that commercial determinants is a valuable framework for understanding the drivers of mental ill health.

Analysis of patient health questionnaire-9 (PHQ-9) based depression prevalence according to a discordance between quantitative urinary cotinine levels and self-report of second-hand smoke exposure among adults: A cross-sectional study

Background

Second-hand smoke (SHS) exposure appears to be more common among individuals with depression. However, self-report of SHS exposure is an inaccurate classification compared to confirming SHS exposure using urinary cotinine (UC). Additionally, the dose-response relationship between depression and UC is controversial.

Methods

The severe stress rate and depression prevalence was estimated among 14530 Korean participants aged ≥19 years using data patient health questionnaire-9 (PHQ-9) and on UC from the Korean National Health and Nutrition Examination Survey. Measured UCs were divided into four categories: UC- (≤0.3 μg/L), UC± (0.4 μg/L-0.9 μg/L), UC+ (1.0 μg/L-11.9 μg/L), and UC++ (≥12.0 μg/L).

Results

About 55.0 % participants were female and participants' mean age was 51.1 years. Non-smokers were 80.3 %. Among non-smokers, non-SHS exposure participants (SR-) and SHS exposure participants (SR+) were 83.0 % and 17.0 %, respectively. When UC- was used as the reference subgroup, the UC++ subgroup showed a higher depression prevalence, whereas the UC ± subgroup showed a lower prevalence. In the same UC categories, the depression prevalence and severe stress rate were higher among females than among males. Furthermore, the SR + subgroup had a higher severe stress rate than the SR- subgroup.

Conclusions

Our study showed a paradoxical reduction in the depression prevalence and severe stress rate in the UC ± subgroup compared to the UC- subgroup. Additionally, the dose-response relationship between the SHS exposure biomarker and the depression prevalence was not linear. Our study indicates that an emotional stress-based model may be more appropriate for explaining the relationship between depression and SHS exposure.

Association between indoor air pollution and depression: a systematic review and meta-analysis of cohort studies

OBJECTIVES

Incomplete combustion of solid fuel and exposure to secondhand smoke (SHS) are the primary causes of indoor air pollution (IAP), potentially leading to detrimental effects on individual mental health. However, current evidence regarding the association between IAP and depression remains inconclusive. This study aims to systematically investigate the evidence regarding the association between IAP and the risk of depression.

DESIGN

Systematic review and meta-analysis of cohort studies.

DATA SOURCES

Two independent reviewers searched PubMed, the Cochrane Library, Web of Science and EMBASE for available studies published up to 13 January 2024.

ELIGIBILITY CRITERIA

We included all cohort studies published in English that aimed to explore the relationship between IAP from solid fuel use and SHS exposure and the risk of depression.

DATA EXTRACTION AND SYNTHESIS

Two independent reviewers extracted data and assessed the risk of bias. The association between IAP and depression was calculated using pooled relative risk (RR) with 95% CIs. Heterogeneity was assessed using the I2 value, and the effect estimates were pooled using fixed-effects or random-effects models depending on the results of homogeneity analysis.

RESULTS

We included 12 articles with data from 61 217 participants. The overall findings demonstrated a significant association between IAP exposure and depression (RR=1.22, 95% CI: 1.13 to 1.31), although with substantial heterogeneity (I2=75%). Subgroup analyses based on pollutant type revealed that IAP from solid fuel use was associated with a higher risk of depression (RR=1.20, 95% CI: 1.13 to 1.26; I2=62%; 5 studies, 36 768 participants) than that from SHS exposure (RR=1.11, 95% CI: 0.87 to 1.41; I2=80%; 7 studies, 24 449 participants). In terms of fuel use, the use of solid fuel for cooking (RR: 1.23, 95% CI: 1.16 to 1.31; I2=58%; 4 studies, 34 044 participants) and heating (RR 1.15, 95% CI: 1.04 to 1.27; I2=65%; 3 studies, 24 874 participants) was associated with increased depression risk.

CONCLUSIONS

The findings from this systematic review and meta-analysis of cohort studies indicated an association between exposure to IAP and depression.

PROSPERO REGISTRATION NUMBER

CRD42022383285.

The effect of secondhand smoke exposure on self-satisfaction and perceived freedom of life choice

Objective: The present study aims to examine whether secondhand smoke exposure (SHSE) in university students can affect three indices of self-satisfaction related to depression as indiced by appearance, weight, and freedom of life choice. Participants: We collected data from 740 nonsmoking students in the summer of 2018, of which 57.84% were exposed to secondhand smoke. Methods: Depressive symptoms, SHSE, smoking status, weight satisfaction, appearance satisfaction, and freedom of life choice were self-reported via a questionnaire. Results: The generalized linear analyses revealed that SHSE was linked to lower scores of perceived freedom of life choice but not significantly associated with weight nor appearance satisfaction. The mediation analyses indicated that perceived freedom of life choice fully mediated the association between SHSE and depressive symptoms. Conclusions: These findings shed light on the importance of SHSE and its effects on mental health in university students. Preventive strategies should therefore locally target university campuses.

Association between secondhand smoke exposure across the life course and depressive symptoms among Chinese older adults

BACKGROUND

There are limited data on the association between secondhand smoke (SHS) exposure across the life course and depressive symptoms among older adults. We aimed to investigate the association of childhood household SHS exposure, adulthood household SHS exposure, lifetime social SHS exposure, and their coexistence with depressive symptoms in older adults.

METHODS

Data were from the 2011-2012 and 2014 waves of the Chinese Longitudinal Healthy Longevity Survey. About 4000 participants (aged 60 years or older) were recruited in a randomly selected half of the counties and cities in China. Data on SHS exposure, past-year depressive symptoms, and covariates were collected using a questionnaire. The chi-square test (for categorical variables) and t-test (for continuous variables) were used to assess differences in the participant characteristics across groups of SHS exposures. We estimated the odds ratios (ORs) and 95 % confidence intervals (CIs) of depressive symptom according to different types of SHS exposure.

RESULTS

Childhood household SHS exposure (OR = 1.42, 95%CI = 1.22-1.66), adulthood household SHS exposure (OR = 1.41, 95%CI = 1.21-1.63) and lifetime social SHS exposure (OR = 1.35, 95%CI = 1.14-1.58) were associated with higher odds of depressive symptoms. Additionally, those with a higher SHS exposure score had higher odds of depressive symptoms (1 point: OR = 1.56, 95%CI = 1.22-2.00; 2 points: OR = 1.77, 95%CI = 1.39-2.25; 3 points: OR = 1.83, 95%CI = 1.45-2.31). The results were similar when stratified by lifetime nonsmoking, former smoking, and current smoking.

LIMITATIONS

Retrospective design may introduce recall bias.

CONCLUSIONS

SHS exposure was associated with higher odds of depressive symptoms in older adults, with the effect seeming to be addictive.

Unhealthy behaviors associated with mental health disorders: a systematic comparative review of diet quality, sedentary behavior, and cannabis and tobacco use

Background

There are well-established literatures documenting the associations between mental disorders and unhealthy behaviors such as poor diet quality, sedentary behavior, and cannabis and tobacco use. Few studies have attempted to understand the respective findings in light of each other, however.

Objective

The purpose of this review was to assemble comparable data for each behavior-disorder association and assess the associations in terms of their overall strength. The review aimed to include a representative, but not exhaustive, range of studies that would allow for explorative comparisons.

Methods

Eligible studies were identified via Pubmed searches and citation searching, restricted to publications no older than 2015 written in English. To obtain comparable data, only studies that reported findings as odds ratios were included, and risk of bias related to study samples, behavioral measurement disparities, and control variables was assessed via sensitivity analyses. Findings for each disorder were compared on the basis of different measures of central tendency.

Results

From 3,682 records, 294 studies were included. The review found evidence of associations between each of the four unhealthy behaviors and psychosis, depression, anxiety, bipolar disorder, attention-deficit/hyperactivity disorder (ADHD), and post-traumatic stress disorder (PTSD), while personality disorder was only investigated in relation to cannabis and tobacco use. In overall comparison, the associations were generally of similar strength, and only the association between cannabis use and personality disorder was exceptional in terms of being significantly stronger than its counterparts across disorders and across behaviors. Analyses of bias risk identified some influence from behavioral measurement disparities and lack of adequate statistical control, but findings were generally robust across a range of sensitivity analyses.

Conclusion

This explorative and comparative review found that poor diet quality, sedentary behavior, and cannabis and tobacco use are about equally strongly associated with a range of different mental disorders. Given the general nature of these associations, we should probably understand them to reflect a general and shared etiology. However, the findings in this review should be regarded as tentative until confirmed by more comprehensive investigations.

Association Between Second-Hand Smoke Exposure and Respiratory Symptoms Among the General Population of Non-smoker Adults in Saudi Arabia: A Cross-Sectional Study

BACKGROUND

Second-hand smoke (SHS) exposure is associated with respiratory symptoms such as cough, dyspnea, and wheezing. However, data on this association in Saudi Arabia is limited.

OBJECTIVES

The objective of this study is to investigate the prevalence of SHS exposure and its association with respiratory symptoms among non-smoker adults in Saudi Arabia.

METHODS

Data collection was carried out over the course of two months by distributing an online questionnaire among adults living in Saudi Arabia. The survey consisted of questions assessing sociodemographic factors, SHS exposure, and the presence of respiratory symptoms. Statistical analysis was performed using IBM SPSS Statistics for Windows, Version 22 (Released 2013; IBM Corp., Armonk, New York, United States). Data was considered significant if p<0.05.

RESULTS

The questionnaire was completed by 1360 participants. Most were females (n=845, 72.1%) and individuals aged 18 to 30 years (n=838, 71.5%). From the analyzed records, 67.3% (n=789) reported SHS exposure. Among them, 40.3% (n=472) reported SHS exposure from household sources, 32.6% (n=382) from work colleagues, and 30.5% (n=357) from friends. The majority (n=306, 76.9%) of those exposed at home reported daily SHS exposure. The main source of home exposure was male family members, particularly the father (n=201, 42.6%). The majority (n=985, 84.0%) of participants reported not having any kind of mold or damage at their place of residence. Individuals with SHS exposure were more likely to report asthma (p=0.043), chest whistling or wheezing (p=0.021), chronic cough (p<0.001), productive cough (p<0.001), and nasal symptoms without a cold (p<0.001). These individuals also demonstrated a higher average symptom score than those not exposed to SHS.  Conclusion: The study reveals that a significant percentage of the Saudi population is exposed to SHS daily, mainly from household sources, especially male family members. A significant association was found between SHS exposure and the presence of respiratory symptoms. Public awareness regarding the prevalence and dangers of SHS exposure is essential in order to alleviate the impact of SHS on the health of the general Saudi population. Additionally, further research is required in this field and demographic group to develop appropriate interventions.

Is secondhand smoke associated with mental health issues? A narrative review of the evidence and policy implications

Secondhand smoke (SHS) is a well-established cause of lung cancer, respiratory disease, heart disease and developmental issues in children, with an overwhelming evidence base spanning over four decades. In this narrative review, we describe studies which have also linked self-reported or cotinine-assessed SHS exposure in the home, workplace and other settings to mental health disorders including depression, suicide, anxiety, and psychological distress in children and adults, sleeping disorders, Attention Deficit Hyperactivity Disorder and behavioural issues in children, and dementia in older adults. In general, evidence indicates that SHS exposure is associated with these disorders in a dose-response manner, with higher odds reported in people who are exposed to SHS at high levels, frequently, and in the home environment. Most studies so far are cross-sectional albeit in large, nationally representative samples from various countries with a smaller number of longitudinal studies. More research is needed in this area to determine whether SHS is a direct cause of adverse mental health outcomes, and whether creating smokefree environments leads to improved mental wellbeing. In particular, more research is needed on the impact of smokefree home environments, an area which has received relatively little focus in smokefree interventions which generally target public places.

Adolescents' exposure to secondhand smoke and its association with susceptibility to smoking and mental health in Lagos, Nigeria

Introduction

this study assessed the relationship between exposure to secondhand smoking (SHS) and its association with self-reported anxiety, depression and susceptibility to smoking among adolescents in Lagos, Nigeria.

Methods

depression among study subjects was determined using the Patient Health Questionnaire-9 (PHQ-9) while the Generalized Anxiety Disorder - 7 (GAD-7) was used to determine anxiety levels. Susceptibility to smoking cigarettes was also determined while the Statistical Package for the Social Science (SPSS) 26.0 software was used for data analysis. Significant associations were determined at P-values <0.05.

Results

of the 300 adolescents surveyed (mean age 12.9±1.43), 7.6 % were regularly exposed to SHS, of which 3.0% were daily exposed to SHS indoors. In multivariable analyses, indoor SHS exposure for ≥ 1 hour daily was associated with increased odds for susceptibility to smoking (AOR=3.793; 95%-CI: 0.98-14.60; p= 0.052) and increased odds for depression (AOR=1.303; 95%-CI: 0.84-2.01; p= 0.228) and slightly reduced odds for anxiety (AOR=0.952; 95%-CI: 0.62-1.47; p=0.822).

Conclusion

secondhand smoking exposure was associated with higher odds of susceptibility to smoking cigarettes and depression among adolescents exposed to SHS, especially among females living in cramped accommodations. Further validation of these findings should however be determined by cohort study designs.

Association between incense burning and prenatal depressive symptoms: evidence from the Born in Guangzhou Cohort Study

This study aimed to examine the association of incense burning alone, a source of indoor air pollution, and jointly with passive smoking, with prenatal depressive symptoms. Information on incense exposure and depressive symptoms were collected at both early and late pregnancy using questionnaires in the Born in Guangzhou Cohort Study. Mixed-effects logistic regression models were used to assess the associations of incense exposure separately, and together with passive smoking, with prenatal depressive symptoms. Compared to the non-users, pregnant women with household incense burning had higher odds of depressive symptoms (odds ratio (OR), 1.17, 95% CI, 1.06, 1.28). Compared with non-users, women who occasionally (OR, 1.22, 95% CI, 1.09, 1.36) and frequently (1.51, 95% CI, 1.26, 1.80) smelled incense had higher odds of prenatal depressive symptoms. Higher duration of incense smelling was associated with higher odds of prenatal depressive symptoms compared with non-users. There was no strong evidence for an interaction of frequency of incense smelling and passive smoking in prenatal depressive symptoms. Prenatal exposure to incense burning was associated with higher odds of having depressive symptoms during pregnancy, and there is no evidence for interaction with concurrent exposure to passive smoking.

Longitudinal association between cardiovascular risk factors and depression in young people: a systematic review and meta-analysis of cohort studies

BACKGROUND

Depression is a common and serious mental illness that begins early in life. An association between cardiovascular disease (CVD) and subsequent depression is clear in adults. We examined associations between individual CVD risk factors and depression in young people.

METHODS

We searched MEDLINE, EMBASE, and PsycINFO databases from inception to 1 January 2020. We extracted data from cohort studies assessing the longitudinal association between CVD risk factors [body mass index (BMI), smoking, systolic blood pressure (SBP), total cholesterol, high-density lipoprotein] and depression, measured using a validated tool in individuals with mean age of 24 years or younger. Random effect meta-analysis was used to combine effect estimates from individual studies, including odds ratio (OR) for depression and standardised mean difference for depressive symptoms.

RESULTS

Based on meta-analysis of seven studies, comprising 15 753 participants, high BMI was associated with subsequent depression [pooled OR 1.61; 95% confidence interval (CI) 1.21-2.14; I2 = 31%]. Based on meta-analysis of eight studies, comprising 30 539 participants, smoking was associated with subsequent depression (pooled OR 1.73; 95% CI 1.36-2.20; I2 = 74%). Low, but not high, SBP was associated with an increased risk of depression (pooled OR 3.32; 95% CI 1.68-6.55; I2 = 0%), although this was based on a small pooled high-risk sample of 893 participants. Generalisability may be limited as most studies were based in North America or Europe.

CONCLUSIONS

Targeting childhood/adolescent smoking and obesity may be important for the prevention of both CVD and depression across the lifespan. Further research on other CVD risk factors including blood pressure and cholesterol in young people is required.

Residential secondhand smoke in a densely populated urban setting: a qualitative exploration of psychosocial impacts, views and experiences

Background

People remain exposed to secondhand smoke, a serious health hazard, inside their home as households face challenges in setting no-smoking rules or are exposed to secondhand smoke drifting in from neighbouring homes. This study explores the psychosocial impacts, views, and experiences with residential secondhand smoke in a densely populated urban setting. 

Methods

In-depth online or face to face interviews with 18 key informants who had been involved in public discourse, policy, advocacy or handling complaints related to residential secondhand smoke, 14 smokers, and 16 non-smokers exposed to secondhand smoke inside their home. All participants were residents of Singapore, a densely populated, multi-ethnic city-state. Interview transcripts were coded in NVivo using a deductive and inductive coding process.

Findings

Secondhand smoke has wide-reaching impacts on physical and psychosocial wellbeing, even if smokers tried to minimise secondhand smoke. Feelings of anxiety and stress are generally tied to feeling discomfort in one’s personal space, a perceived lack of control over the situation, resentment towards smokers, and concerns over the health effects. Family, community, and cultural dynamics add complexities to tackling the issue, especially in patriarchal households. Secondhand smoke exposure from neighbours is considered a widespread issue, exacerbated by structural factors such as building layout and the COVID-19 pandemic. Resolving the issue amicably is considered challenging due to the absence of regulations and a reluctance to stir up conflict with neighbours. While smokers took measures to reduce secondhand smoke, these were described as ineffective by other participants. Smokers appeared to have contrasting views from other participants on what it means to smoke in a socially responsible manner.

Conclusion

Given the wide-reaching psychosocial impacts of residential secondhand smoke, there is a case for stronger interventions, especially in densely populated urban settings where it is more difficult to avoid.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12889-022-13561-7.

Secondhand Smoke in the Workplace Is Associated With Depression in Korean Workers

Background

Smoking negatively affects health, and previous studies argue that secondhand smoke (SHS) has a significantly negative health effect. We investigated whether SHS in the workplace influences workers' depression.

Methods

Three years of data (2014, 2016, and 2018) from the Korean National Health and Nutrition Examination Survey were analyzed. Participants who were not current smokers were classified into the occupational SHS exposed and non-exposed groups. Multivariate logistic regression was performed to estimate odds ratios (ORs) and 95% confidence intervals (CIs) by adjusting various covariates. Stratified analysis with variables, such as year, sex, occupational classification, average working hours, was additionally performed.

Results

The crude ORs of depression was 1.51 (95% CI: 1.27–1.80), and the fully adjusted OR with all the covariates was 1.57 (95% CI: 1.30–1.88). This indicated a significant relationship between occupational SHS and depression. The ORs increased every 2 years: 1.07 (95% CI: 0.79–1.44) in 2014, 1.88 (95% CI: 1.34–2.64) in 2016, and 2.07 (95% CI: 1.43–2.99) in year 2018. Stratification analysis also showed a significant association between SHS and depression among those in the prolonged work hours group and male employees, as well as blue- and white-collar workers.

Conclusion

SHS in the workplace was significantly associated with workers' depression. Our study provides insights into the impact of exposure to SHS for workers and provides a basis for further research and policy-making in this field.

Gender differences in the associations between tobacco smoke exposure and depressive symptoms among U.S. adults: NHANES 2007-2018

BACKGROUND

Findings concerning gender differences in the associations between tobacco smoke exposure (TSE) and depression are inconsistent. This study aimed to investigate the gender-specific associations between active and passive TSE with depressive symptoms in a large, nationally representative sample of U.S. adults.

METHODS

Data were from 27,175 adults aged ≥20 years in the 2007-2018 National Health and Nutrition Examination Survey (NHANES). Depressive symptoms were assessed using the Patient Health Questionnaire-9 (PHQ-9). Multivariable logistic regression was used to adjust for possible confounders. Whether the TSE-depression relationships may differ by age, race/ethnicity, socioeconomic status, body mass index (BMI), and self-reported health status was examined.

RESULTS

After adjustment for lifestyle- and health-related variables, no significant associations between active (OR, 1.16 [95% CI, 0.87-1.55]) and passive TSE (OR, 0.84 [95% CI, 0.59-1.19]) and depressive symptoms were found among men. Among women, active TSE was associated with depressive symptoms (OR, 1.90 [95% CI, 1.51-2.39]), while the association for passive TSE was nonsignificant (OR, 1.11 [95% CI, 0.91-1.34]) after adjusting for lifestyle- and health-related variables. Interaction and subgroup analyses showed that self-reported health status could modify the relationship between passive TSE and depressive symptoms among women. Furthermore, a dose-response relationship between serum cotinine and depressive symptoms was found in women, but not in men.

CONCLUSIONS

This study suggests a stronger TSE-depression association in women than in men. Understanding these gender-specific patterns and identifying the potential moderators of such relationships will enable better targeting of public health interventions.

Association between urine cotinine and depressive symptoms in non-smokers: National representative sample in Korea

BACKGROUND

Secondhand smoke (SHS) exposure is known to have negative effects on mental as well as physical health. However, the association between SHS and mental health problems has not been assessed in non-smokers. To evaluate the association of exposure to tobacco smoke and depressive symptoms, and that of the prevalence of having depressive symptoms and urinary cotinine (UCo) concentrations in non-exposed subjects.

METHODS

Data was extracted from the Korea National Health and Nutrition Examination Survey (KNHANES). Depressive symptoms were determined based on a patient's overall score on the Patient Health Questionnaire (PHQ)-9, and SHS exposure was evaluated using self-reported data and UCo concentration. Overall, 13,219 non-smokers, ≥ 19 years were included in the study. Multinomial logistic regression analysis was conducted to identify factors related to depressive symptoms; independent t-test was conducted to confirm the differences in UCo concentration according to the prevalence of depression.

RESULTS

Among the non-exposure groups, 2.0% of the males and 5.6% of the females showed depressive symptoms. Lower social-economic status, higher UCo concentration, and SHS exposure increased the prevalence of depressive symptoms. The UCo concentration of females with depressive symptoms was significantly higher than those of females without depressive symptoms.

LIMITATIONS

This study only demonstrated an association between SHS exposure and depression, not the causal effects, because of the cross-sectional study design.

CONCLUSION

SHS exposure and depressive symptoms are correlated. The association was also confirmed by evaluating the UCo concentration of those who were not exposed to SHS based on self-reported data.

A meta-review of "lifestyle psychiatry": the role of exercise, smoking, diet and sleep in the prevention and treatment of mental disorders

There is increasing academic and clinical interest in how "lifestyle factors" traditionally associated with physical health may also relate to mental health and psychological well-being. In response, international and national health bodies are producing guidelines to address health behaviors in the prevention and treatment of mental illness. However, the current evidence for the causal role of lifestyle factors in the onset and prognosis of mental disorders is unclear. We performed a systematic meta-review of the top-tier evidence examining how physical activity, sleep, dietary patterns and tobacco smoking impact on the risk and treatment outcomes across a range of mental disorders. Results from 29 meta-analyses of prospective/cohort studies, 12 Mendelian randomization studies, two meta-reviews, and two meta-analyses of randomized controlled trials were synthesized to generate overviews of the evidence for targeting each of the specific lifestyle factors in the prevention and treatment of depression, anxiety and stress-related disorders, schizophrenia, bipolar disorder, and attention-deficit/hyperactivity disorder. Standout findings include: a) convergent evidence indicating the use of physical activity in primary prevention and clinical treatment across a spectrum of mental disorders; b) emerging evidence implicating tobacco smoking as a causal factor in onset of both common and severe mental illness; c) the need to clearly establish causal relations between dietary patterns and risk of mental illness, and how diet should be best addressed within mental health care; and d) poor sleep as a risk factor for mental illness, although with further research required to understand the complex, bidirectional relations and the benefits of non-pharmacological sleep-focused interventions. The potentially shared neurobiological pathways between multiple lifestyle factors and mental health are discussed, along with directions for future research, and recommendations for the implementation of these findings at public health and clinical service levels.

Influence of Second-Hand Smoke and Prenatal Tobacco Smoke Exposure on Biomarkers, Genetics and Physiological Processes in Children-An Overview in Research Insights of the Last Few Years

Children are commonly exposed to second-hand smoke (SHS) in the domestic environment or inside vehicles of smokers. Unfortunately, prenatal tobacco smoke (PTS) exposure is still common, too. SHS is hazardous to the health of smokers and non-smokers, but especially to that of children. SHS and PTS increase the risk for children to develop cancers and can trigger or worsen asthma and allergies, modulate the immune status, and is harmful to lung, heart and blood vessels. Smoking during pregnancy can cause pregnancy complications and poor birth outcomes as well as changes in the development of the foetus. Lately, some of the molecular and genetic mechanisms that cause adverse health effects in children have been identified. In this review, some of the current insights are discussed. In this regard, it has been found in children that SHS and PTS exposure is associated with changes in levels of enzymes, hormones, and expression of genes, micro RNAs, and proteins. PTS and SHS exposure are major elicitors of mechanisms of oxidative stress. Genetic predisposition can compound the health effects of PTS and SHS exposure. Epigenetic effects might influence in utero gene expression and disease susceptibility. Hence, the limitation of domestic and public exposure to SHS as well as PTS exposure has to be in the focus of policymakers and the public in order to save the health of children at an early age. Global substantial smoke-free policies, health communication campaigns, and behavioural interventions are useful and should be mandatory.

Secondhand Smoking and Depressive Symptoms Among In-School Adolescents

INTRODUCTION

Smoking has been linked with depressive symptoms in adolescents, but data on secondhand smoking and depressive symptoms in low- and middle-income countries are scarce. Thus, this study analyzes the association between secondhand smoking and depressive symptoms among in-school adolescents from 22 low- and middle-income countries.

METHODS

Data from the 2003-2008 Global School-Based Student Health Survey were analyzed in June 2019. Data on past-week exposure to secondhand smoke and past-year depressive symptoms were collected. The association between secondhand smoke and depressive symptoms was studied using multivariable logistic regressions and meta-analyses.

RESULTS

The sample consisted of 37,505 adolescents aged 12-15 years who never smoked. The prevalence of depressive symptoms increased from 23.0% in adolescents with no secondhand smoking to 28.9% in those with secondhand smoking every day in the past week. After adjusting for sex, age, food insecurity, and country, there was a dose-response relationship between secondhand smoking and depressive symptoms in the overall sample (0 days: reference; 1-2 days: OR=1.06, 95% CI=0.95, 1.18; 3-6 days: OR=1.38, 95% CI=1.20, 1.58; 7 days: OR=1.63, 95% CI=1.44, 1.86). The country-wise analysis showed that secondhand smoking on at least 3 days (versus <3 days) in the past week was associated with a 1.48-fold increase in the odds of depressive symptoms (95% CI=1.39, 1.59), with a low level of between-country heterogeneity (I²=4.2%).

CONCLUSIONS

There was a positive association between secondhand smoking and depressive symptoms among in-school adolescents from low- and middle-income countries. Further research should investigate causality and assess whether prevention of exposure to secondhand smoke can have a positive effect on the mental well-being of adolescents.