The longitudinal impact of diet, physical activity, sleep, and screen time on Canadian adolescents' academic achievement: An analysis from the COMPASS study.

Adequate amounts of physical activity, sleep, and screen time along with a healthy diet have been demonstrated to have positive associations with academic achievement. No longitudinal study has investigated the simultaneous relationship between all of these behaviours and academic achievement. Data from 11,016 adolescent participants of the COMPASS study in Alberta and Ontario were analysed. Students self-reported their adherence to Canadian recommendations for health behaviours and academic achievement in Math and English on school-based surveys administered in the 2015/16 and 2016/17 waves of COMPASS. Multinomial generalized estimating equations were used to evaluate the association between longitudinal changes in adherence to recommendations and academic achievement at follow-up. Models were adjusted for self-reported sociodemographic information, body weight status, and baseline academic achievement. Students who adhered to a greater number of recommendations performed better than students who adhered to fewer recommendations. Meeting recommendations for Meat and Alternatives (protein-rich foods) and screen time were consistently associated with higher academic achievement compared to students who did not meet these recommendations. A change from not meeting recommendations for Vegetables and Fruit to meeting the recommendation in the following year was associated with higher achievement in both subjects. There was no association between sleep behaviours or physical activity and academic achievement. Results indicate that adherence to recommendations for protein-rich foods, screen time, and vegetables and fruit show promise as behavioural targets for higher academic achievement among youth. Further study using objectives measurements of behaviours and further consideration of socioeconomic variables is merited.

Longitudinal associations of parental and peer influences with physical activity during adolescence: findings from the COMPASS study. / Associations longitudinales entre l'influence des parents et des pairs et l'activité physique durant l'adolescence : résultats de l'étude COMPASS.

INTRODUCTION: To examine temporal variations in parental and peer influences on adolescent physical activity (PA) and whether these variations predicted changes in PA. METHODS: We analyzed data from Years 1, 2 and 3 of the COMPASS study. Participants were 22 909 students in Grades 9 to 12 (mean age [years] = 15.42 ± 1.12, 46% boys, 85% White), who had completed the following survey items on 2 or more consecutive occasions: age, sex, grade, race/ethnicity, moderate-to-vigorous physical activity (MVPA), parental encouragement and parental instrumental support for PA, and number of active peers. We used a linear-mixed model to investigate longitudinal effects of parental and peer influences on changes in square-root transformed average MVPA. We used a generalized-estimating-equations (GEE) model to investigate compliance with Canadian PA guidelines for youth. These models included parental encouragement, instrumental support and number of active peers as time-varying predictors, adjusting for sociodemog raphic factors and grade as covariates, and accounting for the clustering within children and schools. RESULTS: We found that adolescents perceived significantly less parental encouragement and instrumental support and reported fewer active peers as they got older. In addition, the adjusted models suggest that, for a one-unit increase in the score of parental encouragement, parental instrumental support and number of active peers, average MVPA significantly increased by 0.22 units, 0.23 units and 0.16 units, respectively. For the same one-unit increase, adjusted odds of an adolescent complying with the PA guidelines increased by 9%, 4% and 6%, respectively. CONCLUSION: Promoting parental support and facilitating the formation and maintenance of a physically active friendship network may play an important role in attenuating declines in PA during adolescence.

INTRODUCTION: Examiner les variations temporelles de l'influence des parents et des pairs sur l'activité physique des adolescents et vérifier si elles prédisent des changements dans l'activité physique. MÉTHODOLOGIE: Nous avons analysé les données des années 1, 2 et 3 de l'étude COMPASS. Les participants étaient 22 909 élèves de la 9e à la 12e année (âge moyen [ans] = 15,42 ± 1,12; 46 % de garçons; 85 % d'élèves blancs) ayant répondu à deux reprises ou plus et de façon consécutive aux éléments suivants de l'enquête : âge, sexe, année de scolarité, race ou origine ethnique, activité physique modérée à vigoureuse (APMV), encouragement parental et soutien instrumental des parents à l'égard de l'activité physique (AP) et enfin nombre de pairs actifs. Nous avons utilisé un modèle linéaire mixte pour étudier les effets longitudinaux de l'influence des parents et des pairs sur les changements dans l'APMV moyenne avec transformation racine carrée. Nous avons fait appel à un modèle d'équation d'estimation généralisée (EEG) pour examiner l'observance des Directives canadiennes en matière d'activité physique à l'intention des jeunes. Dans ces modèles, l'encouragement parental, le soutien instrumental des parents et le nombre de pairs actifs ont été traités à titre de prédicteurs variant dans le temps. Les modèles ont été ajustés en fonction des facteurs sociodémographiques et de l'année de scolarité (covariables) et ont tenu compte des regroupements des enfants et au sein des écoles. RÉSULTATS: Nous avons constaté que les adolescents, à mesure qu'ils vieillissent, perçoivent significativement moins d'encouragement et de soutien instrumental de leurs parents et déclarent un moins grand nombre de pairs actifs. De plus, les modèles ajustés semblent indiquer que, pour une augmentation d'une unité du score relatif à l'encouragement parental, au soutien instrumental des parents et au nombre de pairs actifs, l'APMV moyenne a considérablement augmenté, de respectivement 0,22, 0,23 et 0,16 unités. Pour l'augmentation d'une unité, la probabilité ajustée qu'un adolescent respecte les directives en matière d'AP s'est accrue de respectivement 9 %, 4 % et 6 %. CONCLUSION: Le fait de promouvoir le soutien parental et de contribuer à la création et au maintien d'un réseau d'amis physiquement actifs pourrait jouer un rôle important dans l'atténuation du déclin de l'activité physique durant l'adolescence.

Searching for rigour in the reporting of mixed methods population health research: a methodological review.

The environments in which population health interventions occur shape both their implementation and outcomes. Hence, when evaluating these interventions, we must explore both intervention content and context. Mixed methods (integrating quantitative and qualitative methods) provide this opportunity. However, although criteria exist for establishing rigour in quantitative and qualitative research, there is poor consensus regarding rigour in mixed methods. Using the empirical example of school-based obesity interventions, this methodological review examined how mixed methods have been used and reported, and how rigour has been addressed. Twenty-three peer-reviewed mixed methods studies were identified through a systematic search of five databases and appraised using the guidelines for Good Reporting of a Mixed Methods Study. In general, more detailed description of data collection and analysis, integration, inferences and justifying the use of mixed methods is needed. Additionally, improved reporting of methodological rigour is required. This review calls for increased discussion of practical techniques for establishing rigour in mixed methods research, beyond those for quantitative and qualitative criteria individually. A guide for reporting mixed methods research in population health should be developed to improve the reporting quality of mixed methods studies. Through improved reporting, mixed methods can provide strong evidence to inform policy and practice.

A systematic review of the effectiveness of school-based obesity prevention programmes for First Nations, Inuit and Métis youth in Canada.

First Nations, Inuit and Métis (FNIM) youth are disproportionately affected by obesity and represent known a high-risk group in Canada. School-based prevention programmes may have the potential to effectively influence obesity-related health behaviours (i.e. healthy eating and physical activity) among this population. We conducted a systematic review of nine electronic databases (2003-2014) to identify studies that describe school-based programmes that have been developed to improve obesity-related health behaviours and outcomes among FNIM youth in Canada. The objectives of this review were to identify and evaluate the effectiveness of these programmes and assess the strength of the methodologies used to evaluate them. Fifteen studies, representing seven distinct interventions, met our inclusion criteria. The majority of these programmes did not result in significant improvements in outcomes related to obesity, healthy eating, or physical activity among FNIM youth. The studies varied in design rigour and use of evaluation activities. The lack of literature on effective school-based programmes for FNIM youth in Canada that target obesity-related outcomes highlights a priority area for future intervention development, evaluation and dissemination within the peer-reviewed literature. Further research is needed on interventions involving Métis and Inuit youth, secondary school-aged FNIM youth and FNIM youth living in urban settings.

Roll-your-own tobacco use among Canadian youth: current prevalence and changes in youth smoking "rollies" since 2008.

INTRODUCTION: Roll-your-own (RYO) cigarettes, or "rollies," represent an affordable alternative to manufactured cigarettes, especially among youth with a lower disposable income. This study characterizes changes in the prevalence of RYO tobacco current use between 2008 and 2010 in Canadian youth and examines the sociodemographic characteristics associated with RYO use in 2010. METHODS: This study uses representative data collected from grade 9 to 12 students as part of the 2008/2009 and 2010/2011 cycles of the Canadian Youth Smoking Survey (YSS). RESULTS: Among current smokers, 30.5% currently use RYO cigarettes. Youth with a disposable income of more than $100 each week were less likely to be current RYO users (OR = 0.49, 95% CI: 0.34-0.71). Current RYO tobacco users were more likely to be current alcohol users (OR = 2.01, 95% CI: 1.09-3.72) or marijuana users (OR = 2.63, 95% CI: 1.73-4.01). CONCLUSION: RYO cigarettes continue to provide an affordable alternative to youth smokers. Targeted school-based prevention programs that address the use of RYO cigarettes may offer additional reductions to the use of RYO cigarettes.

TITRE: Prévalence et variation de la consommation de tabac à rouler chez les jeunes Canadiens depuis 2008. INTRODUCTION: Les cigarettes roulées représentent une solution de rechange abordable par rapport aux cigarettes industrielles, en particulier pour les jeunes à faible revenu. Cette étude a pour but de caractériser les variations de prévalence de la consommation de tabac à rouler des jeunes Canadiens entre 2008 et 2010 et d'examiner les caractéristiques sociodémographiques associées à cette consommation en 2010. MÉTHODOLOGIE: Cette étude utilise des données représentatives recueillies chez des élèves de la 9e à la 12e année dans le cadre des cycles 2008-2009 et 2010-2011 de l'Enquête sur le tabagisme chez les jeunes (ETJ). RÉSULTATS: Parmi les fumeurs, 30,5 % consommaient des cigarettes roulées. Les jeunes bénéficiant d'un revenu disponible de plus de 100 $ par semaine étaient moins nombreux à consommer ce type de produit (rapport de cotes [RC] = 0,49; intervalle de confiance [IC] à 95 % : 0,34 à 0,71). Les consommateurs de tabac à rouler étaient plus nombreux à consommer également de l'alcool (RC=2,01; IC à 95% : 1,09 à 3,72) ou de la marijuana (RC = 2,63; IC à 95 % : 1,73 à 4,01). CONCLUSION: Les cigarettes roulées continuent d'être une solution de rechange abordable pour les jeunes fumeurs. Les programmes de prévention ciblant les consommateurs de cigarettes roulées en milieu scolaire pourraient contribuer à réduire la consommation de ce type de cigarettes.

Are Canadian youth still exposed to second-hand smoke in homes and in cars?

INTRODUCTION: The objective of this manuscript is to examine the prevalence of youth exposed to second-hand smoke (SHS) in homes and cars, changes in SHS exposure over time, and factors associated with beliefs youth hold regarding SHS exposure among a nationally representative sample of Canadian youth. METHODS: Descriptive analysis of SHS exposure in homes and cars was conducted using data from the Canadian Youth Smoking Survey (2004, 2006 and 2008). Logistic regression was conducted to examine factors associated with beliefs youth had about SHS exposure in 2008. RESULTS: In 2008, 21.5% of youth reported being exposed to SHS in their home on a daily or almost daily basis, while 27.3% reported being exposed to SHS while riding in a car at least once in the previous week. Between 2004 and 2008, the prevalence of daily SHS exposure in the home and cars decreased by 4.7% and 18.0% respectively. CONCLUSION: Despite reductions in SHS exposure over time, a substantial number of Canadian youth continue to be exposed to SHS in homes and cars. Further effort is required to implement and evaluate policies designed to protect youth from SHS.

TITRE: Les jeunes Canadiens sont-ils toujours exposés à la fumée secondaire à la maison et en voiture? INTRODUCTION: Nous étudions dans cet article la prévalence de l'exposition à la fumée secondaire (FS) chez les jeunes à la maison et en voiture, les variations du niveau d'exposition à la FS dans le temps et les facteurs associés aux croyances des jeunes au sujet de l'exposition à la FS, grâce à un échantillon représentatif à l'échelle nationale des jeunes Canadiens. MÉTHODOLOGIE: Nous avons mené une analyse descriptive de l'exposition à la FS à la maison et en voiture à l'aide des données de l'Enquête sur le tabagisme chez les jeunes (2004, 2006 et 2008). Une analyse de régression logistique a été effectuée afin d'analyser les facteurs associés aux croyances des jeunes au sujet de l'exposition à la FS en 2008. RÉSULTATS: En 2008, 21,5 % des jeunes ont signalé avoir été exposés à la FS à la maison chaque jour ou presque chaque jour, tandis que 27,3 % des jeunes ont déclaré avoir été exposés à la FS à bord d'une voiture au moins une fois au cours de la semaine précédente. Entre 2004 et 2008, la prévalence de l'exposition quotidienne à la FS au domicile et en voiture a diminué respectivement de 4,7 % et de 18,0 %. CONCLUSION: Malgré la diminution de l'exposition à la FS au fil du temps, un nombre important de jeunes Canadiens continuent à être exposés à la FS chez eux et en voiture. Il faut redoubler d'efforts pour mettre en oeuvre et évaluer des politiques visant à protéger les jeunes de la FS.

Are experimental smokers different from their never-smoking classmates? A multilevel analysis of Canadian youth in grades 9 to 12.

INTRODUCTION: Understanding the characteristics of experimental smoking among youth is critical for designing prevention programs. This study examined which student- and school-level factors differentiated experimental smokers from never smokers in a nationally representative sample of Canadian students in grades 9 to 12. METHODS: School-level data from the 2006 Canadian Census and one built environment characteristic (tobacco retailer density) were linked with data from secondary school students from the 2008-2009 Canadian Youth Smoking Survey and examined using multilevel logistic regression analyses. RESULTS: Experimental smoking rates varied across schools (p < .001). The location (adjusted odds ratio [AOR] = 0.66, 95% CI: 0.49-0.89) of the school (urban vs. rural) was associated with the odds of a student being an experimental smoker versus a never smoker when adjusting for student characteristics. Students were more likely to be experimental smokers if they were in a lower grade, reported low school connectedness, used alcohol or marijuana, believed that smoking can help people relax, received pocket money each week and had a family member or close friend who smoked cigarettes. CONCLUSION: School-based tobacco prevention programs need to be grade-sensitive and comprehensive in scope; include strategies that can increase students' attachment to their school; and address multi-substance use, tobacco-related beliefs and the use of pocket money. These programs should also reach out to students who have smoking friends and family members. Schools located in rural settings may require additional resources.

TITRE: Les fumeurs à titre expérimental sont-ils différents de leurs camarades de classe n'ayant jamais fumé? Une analyse multiniveaux des jeunes Canadiens de la 9e à la 12e année. INTRODUCTION: Il est essentiel de comprendre les caractéristiques du tabagisme expérimental chez les jeunes pour élaborer des programmes de prévention. Dans cette étude, nous avons analysé, à partir d'un échantillon représentatif des élèves canadiens de la 9e à la 12e année, les facteurs relatifs aux élèves et les facteurs relatifs aux écoles qui différenciaient les fumeurs à titre expérimental des élèves n'ayant jamais fumé. MÉTHODOLOGIE: Des données relatives aux écoles recueillies dans le cadre du Recensement de 2006 ainsi qu'une caractéristique relative au milieu bâti (densité des détaillants de produits du tabac) ont été reliées à des données relatives aux élèves du secondaire tirées de l'Enquête sur le tabagisme chez les jeunes de 2008-2009 et ont été soumises à une série d'analyses par régression logistique multiniveaux. RÉSULTATS: Le taux de tabagisme expérimental variait d'une école à l'autre (p < 0,001). Après ajustement en fonction des caractéristiques des élèves, on a observé une association entre l'emplacement (rapport de cotes ajusté = 0,66, intervalle de confiance à 95 % : 0,49 à 0,89) de l'école (milieu urbain ou rural) et le risque qu'un élève soit fumeur à titre expérimental plutôt qu'élève n'ayant jamais fumé. Les élèves étaient plus susceptibles d'être fumeurs à titre expérimental s'ils étaient d'un niveau scolaire inférieur, s'ils avaient un faible sentiment d'appartenance à leur école, s'ils consommaient de l'alcool ou de la marijuana, s'ils croyaient que le tabagisme avait un effet apaisant, s'ils recevaient de l'argent de poche chaque semaine et si un membre de leur famille ou un de leurs amis intimes fumait des cigarettes. CONCLUSION: Les programmes de prévention du tabagisme en milieu scolaire doivent à la fois être adaptés au niveau scolaire et exhaustifs, comprendre des stratégies visant à accroître le sentiment d'appartenance des élèves à leur école et tenir compte du phénomène de polyconsommation, des croyances relatives au tabagisme et de l'utilisation qui est faite de l'argent de poche. Ces programmes devraient également cibler les élèves dont un ami ou un membre de la famille fume. Par ailleurs, les écoles situées en milieu rural pourraient avoir besoin de ressources supplémentaires.

Research methods of the Youth Smoking Survey (YSS).

This paper describes the survey development, design and data collection protocol for the 2008/2009 Youth Smoking Survey (YSS) and the changes to the YSS survey and protocols across the 5 survey cycles (1994, 2002, 2004/2005, 2006/2007, 2008/2009). Canada's Youth Smoking Survey is a nationally representative school-based survey of students (grades 6 to 12 in 2008/2009) from randomly sampled public and private schools in the ten provinces. The main objective of the YSS is to provide benchmark data on national smoking prevalence rates for youth. Key features of the 2008/2009 YSS include consistent measures across survey cycles, a survey team of researchers and non-governmental organizations, a link to school and student level measures, provision of tailored feedback reports to schools and publicly available datasets.

Screen-based sedentary behaviours among a nationally representative sample of youth: are Canadian kids couch potatoes?

PURPOSE: To determine the percentage of Canadian youth meeting screen-time guidelines and to identify characteristics associated with different screen-time behaviours. METHODS: Using nationally representative data collected from the 2008/2009 Youth Smoking Survey (YSS), we analyzed three screen-time behaviours, cigarette smoking, weekly spending money, self esteem, region and grade by sex, and conducted four logistic regression models to examine factors associated with more than 2 hours a day of sedentary screen time. RESULTS: Of 51 922 Canadian youth in grades 6 to 12, 50.9% spent more than 2 hours per day in screen-based behaviours. The average daily screen time was 7.8 (± 2.3) hours. Males and current smokers were more likely to report over 2 hours per day watching TV and videos or playing video games, whereas students in higher grades and those with weekly spending money were more likely to report playing or surfing on a computer. Youth with higher self-esteem were less likely to report spending over 2 hours per day in each of the three screen-time behaviours examined. CONCLUSION: Developing a better understanding of the factors associated with more hours of screen time is required to develop and target interventions that reduce screen-time behaviours.

School-based tobacco-control programming and student smoking behaviour.

The study examined the association of a school-based tobacco-control program with students' smoking behaviour over time using three cross-sectional, provincial census datasets (grade 10 students in 1999, grade 11 students in 2000, grade 12 students in 2001). Data were collected from all secondary schools in Prince Edward Island (Canada) using the Tobacco module of the School Health Action, Planning and Evaluation System (SHAPES). The proportion of regular smokers increased from grade 10 (22.3%) to grade 12 (27.8%, chi(2) = 10.35, df = 1, p < 0.001). Being exposed to different school-based tobacco programs and policies in grades 10 and 11 was not associated with the smoking behaviour of grade 12 students. The strongest predictors of smoking behaviour were having friends or close family members who smoke. This preliminary evidence suggests that programs and policies associated with banning smoking and enforcing smoking restrictions at school may be insufficient unless they also address the influence of smoking peers and family members and link to comprehensive programming within the broader context of other community and policy level interventions.

Cigarette brand preference as a function of price among smoking youths in Canada: are they smoking premium, discount or native brands?

INTRODUCTION: Given that little is known about the price-related cigarette brand preferences of youths, the current study seeks to characterise cigarette brand preferences and examine factors associated with smoking discount or native cigarette brands among Canadian youths who are current smokers. METHODS: This study used nationally representative data collected from 71,003 grade 5-12 students as part of the 2006-7 Canadian Youth Smoking Survey (YSS). Using data from current smokers, logistic regression models were used to examine factors associated with smoking discount or native cigarette brands relative to premium cigarette brands. RESULTS: In 2006, premium cigarettes were the most prevalent brand of cigarette youths report usually smoking (49.4%); a substantial number of youths do report usually smoking either discount (12.9%) or native (9.3%) cigarette brands. Occasional smokers were more likely to report usually smoking premium cigarettes whereas daily smokers were more likely to report smoking either discount or native cigarettes. In particular, discount and native brands appear to be appealing among smoking youths with less spending money or those who are heavier smokers compared to youths smoking premium brands. CONCLUSION: Discount and native cigarette brands are commonly used by a substantial number of smoking youths in Canada. Additional research is required to better understand the reasons behind different cigarette brand preferences and how youths are able to access premium, discount and illicit native cigarettes. Moreover, ongoing surveillance of the cigarette brand preferences of youths is required for guiding future tobacco control policy and programming activities.

A multilevel analysis examining the association between school-based smoking policies, prevention programs and youth smoking behavior: evaluating a provincial tobacco control strategy.

This paper examined how smoking policies and programs are associated with smoking behavior among Grade 10 students (n = 4709) between 1999 and 2001. Data from the Tobacco Module from the School Health Action Planning and Evaluation System were examined using multilevel logistic regression analyses. We identified that (i) attending a school with smoking prevention programs only was associated with a substantial risk of occasional smoking among students with two or more close smoking friends and (ii) attending a school with both smoking prevention programs and policies was associated with substantial risk of occasional smoking among students who did not believe there were clear smoking rules present. Students attending schools where year of enrollment in high school starts in Grade 9 were more likely to be regular and occasional smokers. Each 1% increase in Grade 12 smoking rates increased the odds that a Grade 10 student was an occasional smoker. It appears that grade of enrollment, senior student smoking behavior, close friend's smoking behavior and clear rules about smoking at school can impact school-based tobacco control programming. These preliminary study findings suggest the need for further research targeting occasional smoking behavior and the transition stage into high school.

Youth exposure to smoking in the home and in cars: how often does it happen and what do youth think about it?

AIM: Little is known about what youth think about restricting smoking in their homes or in cars. The present study characterises the frequency of youth being exposed to smoking in their homes and cars, and the beliefs that youth have about restricting people from smoking around youth in those locations. METHODS: Data from the 2004 Youth Smoking Survey (YSS) were used to examine youth exposure to smoking and beliefs about smoking in the home and car among 29,243 Canadian youth in grades 5-9. Logistic regression models were conducted to examine if being exposed to smoking at home or in the car were associated with the beliefs youth have about either smoking around children at home or smoking around children in cars. RESULTS: In 2004, 23.1% of youth in grades 5-9 were exposed to smoking in their home on a daily or almost daily basis, 26.3% were exposed to smoking while travelling in a car at least once in the previous week. The majority of youth reported that they do not think smoking should be allowed around children at home (90.6%) or in cars (90.2%). Males were more likely than females to report that smoking should not be allowed around children at home (OR 1.38) or in cars (OR 1.39). Youth living in a house where someone smokes inside daily were more likely to report that smoking should not be allowed around children at home (OR 1.20) or in cars (OR 1.21). Youth living in a house where the rules do not prevent people from smoking inside were also more likely to report that smoking should not be allowed around children at home (OR 2.07) or in cars (OR 1.76). Youth who have ridden in a car with someone who was smoking cigarettes in the past 7 days were more likely to report that smoking should not be allowed around children in cars (OR 1.73). CONCLUSIONS: It is common for Canadian youth to be exposed to SHS in their homes or while in cars on a frequent basis even though the vast majority of youth do not think smoking should be allowed around children in those locations. This new evidence suggests that programs and policies designed to prevent individuals from smoking around youth in these locations should be a public health priority.

Factors related to adolescents' estimation of peer smoking prevalence.

Although adolescents who overestimate peer smoking prevalence are more likely to smoke, little research has focused on the factors associated with why the majority of adolescents overestimate peer smoking rate. The purpose of this study was to examine demographic, social, environmental and behavioural characteristics related to overestimation of peer smoking prevalence among secondary school students. The current study analysed data collected in two Canadian studies that used the Tobacco Module of the School Health Action, Planning and Evaluation System, a school-based questionnaire. One study surveyed 23 458 students (Grades 9-13) in 29 schools during 2001-02, and the other surveyed 25 452 students in 39 schools in 2003. Results of multiple logistic regression indicate that grade, gender, close friends' smoking, seeing smoking at school, family members' smoking, smoking in the home and smoking status have a clear association with overestimation; school smoking rate and susceptibility to smoking show a tentative relationship and warrant further study. Other factors may also be important for prevalence estimation, and further research is needed to identify these factors. Since adolescents tend to overestimate peer smoking prevalence and perceived prevalence is in turn linked to smoking behaviour, interventions should focus on creating realistic perceptions of smoking prevalence.

Stable isotopes in clinical research: safety reaffirmed.

Approaching half a century of stable-isotope usage in human metabolic studies has been without documented significant adverse effect. Side-effects with acute D dosing are transitory with no demonstrated evidence of permanent deleterious action. The threshold of D toxicity has been defined in animals and is far in excess of concentrations conceivably used in human studies. The possibility that D may have additional beneficial pharmacological applications cannot be excluded. For isotopes other than D, evidence of observed toxicity remains to be produced even at dosages far in excess of the range used in metabolic studies. Absence of adverse effect may be attributable to small mass differences and the similar properties of tracer and predominantly abundant isotope. Absolute determination of stable isotope toxicity in humans is rendered impossible by ethical considerations. Also, the precision of extrapolating toxicity thresholds from animal studies remains unknown. However, should perturbation of the delicate homoeostatic characteristic of living organisms occur with use of stable isotopes, it is almost undoubtedly at some level of administration greatly in excess of those administered currently in biomedical research.