Does misclassification of former tobacco smokers explain the 'smoker's paradox' in the risk of COVID-19? Insights from the Stockholm Public Health Cohort

BACKGROUND

The association between tobacco smoking and the risk of COVID-19 and its adverse outcomes is controversial, as studies reported contrasting findings. Bias due to misclassification of the exposure in the analyses of current versus non-current smoking could be a possible explanation because former smokers may have higher background risks of the disease due to co-morbidity. The aim of the study was to investigate the extent of this potential bias by separating non-, former, and current smokers when assessing the risk or prognosis of diseases.

METHODS

We analysed data from 43,400 participants in the Stockholm Public Health Cohort, Sweden, with information on smoking obtained prior to the pandemic. We estimated the risk of COVID-19, hospital admissions and death for (a) former and current smokers relative to non-smokers, (b) current smokers relative to non-current smokers, that is, including former smokers; adjusting for potential confounders (aRR).

RESULTS

The aRR of a COVID-19 diagnosis was elevated for former smokers compared with non-smokers (1.07; 95% confidence interval (CI) =1.00-1.15); including hospital admission with any COVID-19 diagnosis (aRR= 1.23; 95% CI = 1.03-1.48); or with COVID-19 as the main diagnosis (aRR=1.23, 95% CI= 1.01-1.49); and death within 30 days with COVID-19 as the main or a contributory cause (aRR=1.40; 95% CI=1.00-1.95). Current smoking was negatively associated with risk of COVID-19 (aRR=0.79; 95% CI=0.68-0.91).

CONCLUSIONS

Separating non-smokers from former smokers when assessing the disease risk or prognosis is essential to avoid bias. However, the negative association between current smoking and the risk of COVID-19 could not be entirely explained by misclassification.

Current tobacco use and COVID-19 diagnoses in a cohort of adult clients of public dental clinics in Sweden

Smoking has been linked with both increased and decreased risk of COVID-19, prompting the hypothesis of a protective role of nicotine in the pathogenesis of the disease. Studies of the association between use of smokeless tobacco and COVID-19 would help refining this hypothesis. We analysed data from 424,386 residents in the Stockholm Region, Sweden, with information on smoking and smokeless tobacco (snus) use prior to the pandemic obtained from dental records. Diagnoses of COVID-19 between February and October 2020 were obtained from health-care registers. We estimated the risk of receiving a diagnosis of COVID-19 for current smokers and for current snus users relative to non-users of tobacco, adjusting for potential confounders (aRR). The aRR of COVID -19 was elevated for current snus users (1.09 ;95%CI = 0.99-1.21 among men and 1.15; 95%CI = 1.00-1.33 among women). The risk for women consuming more than 1 can/day was twice as high as among non-users of tobacco. Current smoking was negatively associated with risk of COVID-19 (aRR = 0.68; 95% CI = 0.61-0.75); including hospital admission (aRR = 0.60; 95% CI = 0.47-0.76) and intensive care (aRR = 0.43; 95% CI = 0.21-0.89). The hypothesis of a protective effect of tobacco nicotine on COVID-19 was not supported by the findings. The negative association between smoking and COVID-19 remains unexplained.

Increasing Children's physical Activity by Policy (CAP) in preschools within the Stockholm region: study protocol for a pragmatic cluster-randomized controlled trial

Background

Systematic reviews suggest that preschool environmental/organizational changes may be effective in increasing physical activity (PA) levels of preschool children, but evidence is scarce regarding feasible, effective, and equitable interventions that can be scaled up. Specifically, it is essential to understand whether introducing a multicomponent organizational change in terms of policy in the preschool context may be beneficial for children’s PA levels and concomitant health outcomes. To bridge this knowledge gap, our main aim is to examine the feasibility and effectiveness of a policy package in increasing PA levels in preschool children, using a large-scale pragmatic cluster-randomized controlled trial.

Methods

This proposed study is a pragmatic cluster-randomized controlled trial with two conditions (intervention and control with a 1:1 ratio) with preschools as clusters and the unit of randomization. We aim to recruit approximately 4000 3–5-year-old children from 90 preschools and retain more than 2800 children from 85 preschools to provide adequate statistical power for the analyses. The intervention to implement is a co-created, multicomponent policy package running for 6 months in preschools randomized to intervention. Change in accelerometer measured PA levels in children between intervention and control from pre- and post-intervention will be the primary outcome of the study, while secondary outcomes include health outcomes such as musculoskeletal fitness, psychosocial functioning, and absence due to illness in children among others. Implementation will be studied carefully using both quantitative (dose, fidelity) and qualitative (interview) methodologies. The change in primary and secondary outcomes, from pre- to post-intervention, will be analyzed with linear mixed-effect models (to allow both fixed and random effects) nested on a preschool level.

Discussion

This is a large-scale co-creation project involving the City of Stockholm, childcare stakeholders, preschool staff, and the research group with the potential to influence more than 30,000 preschool children within the Stockholm area. The study will add reliable evidence for the implementation of PA policies at the organizational level of preschools and clarify its potential effect on objectively measured PA and health markers in children.

Trial registration

ClinicalTrials.govNCT04569578. Prospectively registered on September 20, 2020.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-022-06513-4.

Electronic cigarette use and smoking cessation in cohort studies and randomized trials: A systematic review and meta-analysis

INTRODUCTION

The aim of this systematic review and meta-analysis was to assess the association between e-cigarette use and subsequent smoking cessation in cohort studies and randomized controlled trials (RCT).

METHODS

A systematic literature search was finalized 11 November 2019 using EMBASE, Cochrane Library, Scopus, PubMed Health, NICE evidence search, PROSPERO, CRD, PsycInfo, and PubMed including Medline. Inclusion criteria were: reporting empirical results; longitudinal observational design with a minimum of 3 months of follow-up; including general population samples; and allowing for comparison between users and non-users of e-cigarettes. Studies rated as having high risk of bias were excluded. The procedures described by PRISMA were followed, and the quality of evidence was rated using GRADE.

RESULTS

Twenty-eight longitudinal, peer-reviewed publications from 26 cohort studies, and eight publications from seven RCTs assessing the association between e-cigarette use and smoking cessation were included in this review. A random-effects meta-analysis based on 39147 participants in cohort studies showed a pooled unadjusted odds ratio (OR) for smoking cessation among baseline e-cigarette users compared with baseline non-users of 0.97 (95% CI: 0.67-1.40), while the adjusted OR was 0.90 (95% CI: 0.63-1.27). The pooled odds ratio for smoking cessation in RCTs was 1.78 (95% CI: 1.41-2.25). The evidence for cohort studies was graded as very low and for RCTs as low.

CONCLUSIONS

We did not find quality evidence for an association between e-cigarette use and smoking cessation. Although RCTs tended to support a more positive association between e-cigarette use and smoking cessation than the cohort studies, the grading of evidence was consistently low.

Protocol for the evaluation of cost-effectiveness and health equity impact of a school-based tobacco prevention programme in a cluster randomised controlled trial (the TOPAS study)

INTRODUCTION

Despite a long-term downward trend in smoking prevalence, tobacco remains the number one risk factor for death and disability in Sweden. Globally, tobacco use generates a substantial economic burden for health systems and is also a major driver of socioeconomic inequalities in health. This article describes the planned cost-effectiveness and health equity impact evaluation of a multicomponent school-based programme to prevent the onset of tobacco use in adolescents.

METHODS AND ANALYSIS

Cost-effectiveness of the multicomponent Tobacco-Free Duo programme will be evaluated against the educational component of the same programme only. An incremental cost-effectiveness ratio (ICER) will be calculated in terms of the cost per case prevented using the trial primary outcome and within-trial payer costs. If the ICER is negative, an incremental net benefit ratio will be calculated. Robustness of the results will be assessed through one-way sensitivity analyses. The slope index of inequality will be computed to assess the potential impact of the Tobacco-free Duo programme on education-related inequalities in the onset of smoking and in adult smoking cessation, comparing the two trial arms.

ETHICS AND DISSEMINATION

Ethical approval was obtained from the Regional Ethics Review Board, Umeå (registration number 2017/255-31). The Public Health Agency of Sweden commissioned the study. The findings will be disseminated internationally within academia and to national and local policy-makers.

TRIAL REGISTRATION NUMBER

ISRCTN52858080; Pre-results.

Unfavourable sedentary and physical activity behaviour before and after retirement: a population-based cohort study

BACKGROUND

During transition to retirement there is often a rearrangement of daily life which might provide a key opportunity for interventions to promote a non-sedentary and active lifestyle. To be able to design effective interventions, it is essential to know which sedentary and physical behaviour domains (eg, at home or during leisure time) have potential to facilitate healthy ageing during the retirement transition.

OBJECTIVE

To determine whether unfavourable sedentary and physical activity behaviour before retirement predict unfavourable sedentary and physical activity behaviour after retirement.

DESIGN

Population-based cohort.

SETTING AND PARTICIPANTS

Adults (n=3272) employed in 2010 but retired in 2014.

METHODS

Self-reported preretirement job activity, sedentary leisure time, physical activity at home, and walking-cycling and exercise were assessed as predictors for unfavourable sedentary and physical activity behaviours after retirement using logistic regression. Unfavourable behaviours were defined based on the respective median of the cohort distribution. Furthermore, the OR for having multiple unfavourable behaviours after retirement was determined, based on the amount of unfavourable behaviours before retirement. All models were adjusted for gender and education.

RESULTS

Unfavourable preretirement physical activity and sedentary behaviour at home or during leisure time were the strongest predictors of the same behaviours after retirement. Unfavourable job activity did not predict physical activity but did predict unfavourable sedentary behaviour after retirement (OR=1.66, 95% CI 1.41 to 1.96). Unfavourable exercise behaviour before retirement predicted unfavourable sedentary and physical activity after retirement in all domains. With all behaviours being unfavourable before retirement, the OR of having at least three unfavourable behaviours after retirement was 36.7 (95% CI 16.8 to 80.5).

CONCLUSIONS

Adults with a higher number of unfavourable preretirement physical activity and sedentary behaviours are likely to carry these unfavourable behaviours into retirement age. Interventions should target those with more unfavourable preretirement physical activity and sedentary behaviours before retirement, and those interventions focusing on exercise might have greatest potential.

Effect of tobacco control policies on the Swedish smoking quitline using intervention time-series analysis

OBJECTIVES

To coherently examine the responsiveness of the Swedish National Tobacco Quitline (SNTQ) to different types of anti-smoking policies over an extended period of calendar time.

DESIGN

Quasi-experimental design with an intervention time-series analysis based on 19 years series of data collected between January 1999 and August 2017 (224 months). Statistical inference on calling rates and rate ratios was obtained using intervention time-series models (Poisson regression and transfer functions).

PARTICIPANTS

A total of 179 851 phone calls to the SNTQ.

INTERVENTIONS

Recent application of the 2014/40/ European Union (EU) Tobacco Products Directive in 2016. Historical interventions such as a campaign on passive smoking in January 2001; introduction of larger text warnings on cigarette packages since September 2002; banning smoking in restaurants since June 2005; and tobacco tax increase by 10% since January 2012.

OUTCOME MEASURE

Calling rates to the SNTQ expressed per 100 000 smokers.

SETTING

Sweden.

RESULTS

The introduction of large pictorial warnings together with text warnings on cigarette packages (May 2016) was associated with a 35% increase in SNTQ calling rate (95% CI 1.16 to 1.57). The campaign on passive smoking (Jan 2001) was associated with a 61% higher calling rate (95% CI 1.06 to 2.45). Larger text warnings on cigarette packs (Sept 2002) conferred a 28% increment in the calling rate (95% CI 1.15 to 1.42); and prohibition to smoke in restaurants (Jun 2005) was associated with a 15% increase in the calling rate (95% CI 1.01 to 1.30). The 10% tobacco tax increase (Jan 2012) was associated with a 3% higher calling rate (95% CI 0.90 to 1.19).

CONCLUSIONS

Within an overall decreasing trend of daily smoking in Sweden, we found that the recent introduction of pictorial warnings together with text warnings and referral text had a discernible positive impact on the calling rates to the smoking quitline. We were also able to detect a likely impact of earlier nationwide interventions.

Association between adolescents' academic aspirations and expectations and mental health: a one-year follow-up study

Background

Mental health problems among youth have increased in Sweden in recent decades, as has competition in higher education and the labour market. It is unknown whether the increasing emphasis put on educational achievement might negatively affect adolescents' mental health. We aimed to investigate the relationship between adolescents' academic aspirations and expectations and the risk of mental health problems.

Methods

We studied 3343 Swedish 7th grade adolescents (age 13), who participated in the first two waves of the KUPOL longitudinal study; participants answered a questionnaire encompassing the five-item Future Aspirations and Goals (FG) subscale of the Student Engagement Instrument, two questions about their own academic aspirations and expectations and two mental health instruments: the Center for Epidemiological studies for Children (CES-DC) (α=.90) and the Strengths and Difficulties Questionnaire (SDQ) (α=.78). The association between aspirations and expectations at baseline and mental health at follow-up was analysed using logistic regression models adjusting for baseline mental health, socio-demographic and family factors.

Results

The FG subscale was inversely and linearly associated with the odds of high CES-DC score [adjusted OR (odds ratio) 0.71, 95% CI (confidence interval): 0.59-0.86], total Strengths and Difficulties Questionnaire score (OR 0.59, 95% CI 0.49-0.71), and its internalizing (OR 0.70, 95% CI 0.59-0.84) and externalizing problems scores (OR 0.58, 95% CI 0.48-0.71).

Conclusions

Adolescents with high individual academic aspirations have less mental health problems at 1-year follow-up. Future studies should investigate whether interventions aimed at increasing aspirations and engagement in school may prevent mental health problems in adolescence.

Health behaviours as a predictor of quitting hazardous alcohol use in the Stockholm Public Health Cohort

Background

Adopting healthy behaviours may facilitate the transition from hazardous to non-hazardous use of alcohol, yet, longitudinal studies of health behaviours in relation to the cessation of hazardous alcohol use are rare. We addressed this question using data from a large population-based cohort of adults in Sweden (Stockholm Public Health Cohort).

Methods

Participants from two sub-cohorts (inception in 2002 and 2010), with follow-up until the year 2014 were included. Health behaviours (tobacco use, diet and physical activity) and alcohol use were self-reported in questionnaire-based surveys. Hazardous alcohol use was defined as either usual weekly consumption (2002 sub-cohort) or heavy occasional alcohol consumption (2010 sub-cohort). Baseline hazardous drinkers with complete data constituted the analytical sample (n = 8946). Logistic regression was used to calculate the Odds Ratios and their 95% confidence intervals of quitting hazardous alcohol use, with tobacco use, diet and physical activity as predictors of change.

Results

In the 2002 sub-cohort, 28% reported non-hazardous use sustained through two consecutive follow-up points. In the 2010 sub-cohort, 36% of the participants reported non-hazardous use of alcohol at follow-up. Favourable health behaviours at baseline (e.g. no tobacco use, sufficient fruit intake and physical activity) were associated with a 19% to 75% higher of odds quitting hazardous alcohol use. Further, favourable changes in diet and tobacco cessation were associated with non-hazardous alcohol use at follow-up.

Conclusions

As many as one-third of hazardous alcohol users may quit this drinking pattern in a medium-long term. Holding or achieving a healthy lifestyle may facilitate this transition.

Do unfavourable alcohol, smoking, nutrition and physical activity predict sustained leisure time sedentary behaviour? A population-based cohort study

Comparing lifestyle of people remaining sedentary during longer periods of their life with those favourably changing their behaviour can provide cues to optimize interventions targeting sedentary behaviour. The objective of this study was to determine lifestyle predictors of sustained leisure time sedentary behaviour and assess whether these predictors were dependent on gender, age, socioeconomic position and occupational sedentary behaviour. Data from a large longitudinal population-based cohort of adults (aged 18-97years) in Stockholm responding to public health surveys in 2010 and 2014 were analysed (n=49,133). Leisure time sedentary behaviour was defined as >3h per day of leisure sitting time e.g. watching TV, reading or using tablet. Individuals classified as sedentary at baseline (n=9562) were subsequently categorized as remaining sedentary (n=6357) or reduced sedentary behaviour (n=3205) at follow-up. Lifestyle predictors were unfavourable alcohol consumption, smoking, nutrition, and physical activity. Odds ratios (OR) and corresponding 95% Confidence Intervals (CI) were calculated, adjusting for potential confounders. Unfavourable alcohol consumption (OR=1.22, CI:1.11-1.34), unfavourable candy- or cake consumption (OR=1.15, CI:1.05-1.25), and unfavourable physical activity in different contexts were found to predict sustained sedentary behaviour, with negligible differences according to gender, age, socioeconomic position and occupational sedentary behaviour. People with unfavourable lifestyle profiles regarding alcohol, sweets, or physical activity are more likely to remain sedentary compared to sedentary persons with healthier lifestyle. The impact of combining interventions to reduce leisure time sedentary behaviour with reducing alcohol drinking, sweet consumption and increasing physical activity should be tested as a promising strategy for behavioural modification.

Economic evaluation of a brief counselling for smoking cessation in dentistry: a case study comparing two health economic models

OBJECTIVES

This study aimed to compare the cost-effectiveness estimates of a brief counselling of smoking cessation in dentistry by using two different health economic models.

DESIGN AND OUTCOME MEASURES

Intervention effectiveness was estimated in a cluster randomised controlled trial. The number of quitters was estimated based on 7-day abstinence and on smoking reduction at follow-up. Health economic evaluation was performed using two models: (1) a population-based model employing potential impact fractions and (2) a Markov model estimating the cost-effectiveness of the intervention for the actual participants. The evaluation was performed from healthcare and societal perspectives, and health gains were expressed in quality-adjusted life-years (QALYs).

SETTING

Dental clinics in Sweden.

PARTICIPANTS

205 Swedish smokers aged 20-75 years.

INTERVENTIONS

A brief, structured behavioural intervention was compared with 'usual care'.

RESULTS

The cost per quitter was US$552 in the intervention and US$522 in the 'usual care' condition. The net saving estimated with the population-based model was US$17.3 million for intervention and US$49.9 million for 'usual care', with health gains of 1428 QALYs and 2369 QALYs, respectively, for the whole Swedish population during 10 years. The intervention was thus dominated by 'usual care'. The reverse was true when using the Markov model, showing net societal savings of US$71 000 for the intervention and US$57000 for 'usual care', with gains of 5.42 QALYs and 4.74 QALYs, respectively, for lifelong quitters.

CONCLUSION

The comparison of intervention and 'usual care' derived from small-scale studies may be highly sensitive to the choice of the model used to calculate cost-effectiveness.

TRIAL REGISTRATION

The cluster randomised trial is registered in the ISRCTN register of controlled trials with identification number ISRCTN50627997.

Effectiveness of interventions on physical activity in overweight or obese children: a systematic review and meta-analysis including studies with objectively measured outcomes

There is no consensus on interventions to be recommended in order to promote physical activity among overweight or obese children. The objective of this review was to assess the effects on objectively measured physical activity, of interventions promoting physical activity among overweight or obese children or adolescents, compared to no intervention or to interventions without a physical activity component. Publications up to December 2015 were located through electronic searches for randomized controlled trials resulting in inclusion of 33 studies. Standardized mean differences from baseline to post-intervention and to long-term follow-up were determined for intervention and control groups and meta-analysed using random effects models. The meta-analysis showed that interventions had no effect on total physical activity of overweight and obese children, neither directly post-intervention (-0.02 [-0.15, 0.11]) nor at long-term follow-up (0.07 [-0.27, 0.40]). Separate analyses by typology of intervention (with or without physical fitness, behavioural or environmental components) showed similar results (no effect). In conclusion, there is no evidence that currently available interventions are able to increase physical activity among overweight or obese children. This questions the contribution of physical activity to the treatment of overweight and obesity in children in the studied interventions and calls for other treatment strategies.

Evaluation of a brief counseling for tobacco cessation in dental clinics among Swedish smokers and snus users. A cluster randomized controlled trial (the FRITT study)

OBJECTIVE

The aim of this study is to assess the effectiveness of a very brief structured counseling for tobacco cessation in dentistry clinics.

METHOD

A cluster randomized trial was conducted in Sweden in 2012-2013. Twenty-seven dentistry clinics in two Swedish counties were randomized to provide either a structured brief advice based on the 5 A's model or usual care. Participants were 467 patients currently using tobacco daily (225 in the intervention group and 242 in usual care), of which 97% were retained at follow-up, six months after enrolment. Study outcomes were: 7-day abstinence (primary outcome); 3-month sustained abstinence; 50% reduction of the amount tobacco used; quit attempts lasting at least 24h.

RESULTS

Compared to usual care, brief counseling was not associated to statistically significant increase in the proportion abstinent from tobacco use after 6months. However, there was a statistically significant association with reduction of tobacco consumption (OR=2.07 95% CI 1.28-3.35). Changes in the expected direction for all outcomes were more frequent in the intervention than in the usual care group, and larger among exclusive snus users than among smokers.

CONCLUSIONS

Very brief and structured counseling in dentistry may achieve positive behavioral modifications among tobacco users, with significant reduction of tobacco consumption, particularly among smokeless tobacco users.

Snus (Swedish smokeless tobacco) use and risk of stroke: pooled analyses of incidence and survival

BACKGROUND

Snus is a moist smokeless tobacco product with high nicotine content. Its use has a short-term effect on the cardiovascular system, but the relationship between snus use and stroke is unclear.

OBJECTIVE

The aim of this study was to assess the associations between use of snus and incidence of and survival after stroke, both overall and according to subtypes.

METHODS

Pooled analyses of eight Swedish prospective cohort studies were conducted, including 130 485 men who never smoked. We estimated hazard ratios (HRs) with 95% confidence intervals (CIs) of incidence and death after diagnosis using Cox proportional hazard regression models and case fatality and survival using logistic regression and Kaplan-Meier methods, respectively.

RESULTS

No associations were observed between the use of snus and the risk of overall stroke (HR 1.04, 95% CI 0.92-1.17) or of any of the stroke subtypes. The odds ratio (OR) of 28-day case fatality was 1.42 (95% CI 0.99-2.04) amongst users of snus who had experienced a stroke, and the HR of death during the follow-up period was 1.32 (95% CI 1.08-1.61).

CONCLUSION

Use of snus was not associated with the risk of stroke. Hence, nicotine is unlikely to contribute importantly to the pathophysiology of stroke. However, case fatality was increased in snus users, compared with nonusers, but further studies are needed to determine any possible causal mechanisms.

Use of snus and risk for cardiovascular disease: results from the Swedish Twin Registry

OBJECTIVE

To study the association between snus use and the risk for cardiovascular disease, i.e. ischemic heart disease and stroke.

DESIGN

Cohort study.

SETTING

Sweden.

SUBJECTS

Sixteen thousand six hundred and forty-two male Swedish twins participating in the Screening Across the Lifespan Twin Study, conducted in 1998- 2002, were followed for incident cardiovascular disease. Participants were without a history of cardiovascular disease at baseline and incident cases were identified via the Swedish Cause of Death Register and Hospital Discharge Register.

RESULTS

Overall, there was no association between use of snus and risk for cardiovascular disease. Current snus users, without a smoking history, had a relative risk of 1.00 (95% confidence interval 0.69-1.46) for cardiovascular disease as compared to non users. Corresponding relative risks for ischemic heart disease and stroke were 0.85 (95% confidence interval 0.51-1.41) and 1.18 (95% confidence interval 0.67-2.08), respectively. In smoking adjusted models, risk estimates for ischemic heart disease in relation to snus use were all close to unity regardless of timing or intensity of snus use. However, current heavy snus users (consuming more than four cans week(-1)) had a relative risk for stroke of 1.75 (95% confidence interval 0.95-3.21).

CONCLUSION

These data do not support any strong association between snus use and risk for cardiovascular disease.

Is universal prevention against youths' substance misuse really universal? Gender-specific effects in the EU-Dap school-based prevention trial

BACKGROUND

Studies of effectiveness of school-based prevention of substance misuse have generally overlooked gender differences. The purpose of this work was to analyse gender differences in the effectiveness of a new European school-based curriculum for prevention of substance misuse among adolescents.

METHODS

The European Drug Abuse Prevention (EU-Dap) trial took place in seven European countries during the school year 2004-05. Schools were randomly assigned to either a control group or a 12-session standardised curriculum ("Unplugged") based on a comprehensive social influence model. The analytical sample consisted of 6359 students (3324 boys and 3035 girls). The use of cigarettes, alcohol and illicit drugs, adolescents' knowledge and opinions about substances, as well as social and personal skills were investigated through a self-completed anonymous questionnaire administered at enrollment and 3 months after the end of the programme. Adjusted Prevalence Odds Ratios were calculated as the measure of association between the intervention and behavioural outcomes using multilevel regression modelling.

RESULTS

At enrollment, boys were more likely than girls to have used cannabis and illicit drugs, whereas girls had a higher prevalence of cigarette smoking. At the follow-up survey, a significant association between the programme and a lower prevalence of all behavioural outcomes was found among boys, but not among girls. Age and self-esteem emerged as possible modifiers of these gender differences, but effects were not statistically significant.

CONCLUSIONS

Comprehensive social influence school curricula against substance misuse in adolescence may perform differently among girls and boys, owing to developmental and personality factors.

Quitting cigarettes completely or switching to smokeless tobacco: do US data replicate the Swedish results?

BACKGROUND

Swedish male smokers are more likely than female smokers to switch to smokeless tobacco (snus) and males' smoking cessation rate is higher than that of females. These results have fuelled international debate over promoting smokeless tobacco for harm reduction. This study examines whether similar results emerge in the United States, one of few other western countries where smokeless tobacco has long been widely available.

METHODS

US DATA SOURCE: national sample in Tobacco Use Supplement to Current Population Survey, 2002, with 1-year follow-up in 2003. Analyses included adult self-respondents in this longitudinal sample (n = 15,056). Population-weighted rates of quitting smoking and switching to smokeless tobacco were computed for the 1-year period.

RESULTS

Among US men, few current smokers switched to smokeless tobacco (0.3% in 12 months). Few former smokers turned to smokeless tobacco (1.7%). Switching between cigarettes and smokeless tobacco, infrequent among current tobacco users (<4%), was more often from smokeless to smoking. Men quit smokeless tobacco at three times the rate of quitting cigarettes (38.8% vs 11.6%, p<0.001). Overall, US men have no advantage over women in quitting smoking (11.7% vs 12.4%, p = 0.65), even though men are far likelier to use smokeless tobacco.

CONCLUSION

The Swedish results are not replicated in the United States. Both male and female US smokers appear to have higher quit rates for smoking than have their Swedish counterparts, despite greater use of smokeless tobacco in Sweden. Promoting smokeless tobacco for harm reduction in countries with ongoing tobacco control programmes may not result in any positive population effect on smoking cessation.

Maternal smoking during pregnancy: a comparison between concurrent and retrospective self-reports

Retrospective reports of smoking in pregnancy are of importance for clinical or scientific purposes. Careful analyses of stability and accuracy of recalled behaviour are, therefore, needed. In 1998, the mothers of 2369 pre-teens born in Sweden retrospectively reported their smoking behaviour during the first trimester of the index pregnancy. We matched these reports with those recorded by midwives at the beginning of the index pregnancy, using information from the Swedish Medical Birth Registry. Using this registry as gold standard, the sensitivity and specificity of the retrospective reports containing any smoking were 83.9% and 92.8% respectively, but the sensitivity was low for daily smoking, 56.0%. Of the 222 discordant reports, 19.0% were due to mothers recalling daily smoking which was not reported at the time of pregnancy, and 42% were due to failure to recall smoking reported at the time of pregnancy, while the remaining 39% retrospectively reported occasional smoking, whereas they were registered as non-daily smokers when pregnant. Retrospective recall of pregnancy smoking is fairly stable over time.

Cigarette smoking and the risk of goitre and thyroid nodules amongst parous women

OBJECTIVES

To clarify the mechanisms by which smoking is associated to toxic and nontoxic goitre and thyroid nodules.

DESIGN

Cohort study.

SETTING

Sweden.

SUBJECTS

A cohort of 874,507 parous women identified through the Medical Birth Registry, with smoking behaviour assessed through self-reported information at the first pre-natal visit, and follow-up between 1983 and 1997.

MAIN OUTCOME MEASURES

Hospital diagnoses of toxic and nontoxic goitre and thyroid nodules, identified by record-linkage with the national Inpatient Registry. Cox regression was employed to estimate the hazard ratio (HR) of smokers compared with nonsmokers and the corresponding 95% confidence limits (CL).

RESULTS

There was a significantly increased risk of goitre and nodules amongst smokers. The positive association was stronger for toxic (age adjusted HR = 1.94, CL = 1.74-2.16) than for nontoxic goitre and nodules (age-adjusted HR = 1.26; CL = 1.14-1.38). There was generally no clear risk trend with regard to amount smoked (below and above 10 cigarettes per day). Elevated body mass attenuated these associations, whilst being born in Swedish areas of endemic goitre enhanced the association with nontoxic goitre and nodules.

CONCLUSIONS

Smoking enhances the risk of thyroid goitre and nodules requiring hospital admission. Iodine deficiency and body weight are likely to be important modifiers of the risk of thyroid hyperplastic diseases amongst smokers.

Validity of self reports in a cohort of Swedish adolescent smokers and smokeless tobacco (snus) users

OBJECTIVE

To validate self reports of cigarette and smokeless tobacco (snus) use in a prospective cohort of adolescents.

DESIGN

A cross sectional analysis of a cohort sub-sample.

SETTING

County of Stockholm, Sweden.

SUBJECTS

520 adolescents in the final grade of junior high school (mean age 15.0 years).

MAIN OUTCOME MEASURE

Concordance between self reported tobacco use and saliva cotinine concentration.

RESULTS

Using a cut point of 5 ng/ml saliva cotinine to discriminate active tobacco use, there was a 98% concordance between self reported non-use in the past month and cotinine concentration. The sensitivity of the questionnaire compared to the saliva cotinine test, used as the gold standard, was 90% and the specificity 93%. One hundred and fifteen out of 520 subjects (22%) reported monthly tobacco use. Among these, 67% (46/69) of the exclusive cigarette smokers, 82% (23/28) of exclusive snus users, and 94% (15/16) of mixed users (cigarettes + snus) had cotinine concentrations above 5 ng/ml. Among subjects reporting daily use 96% (64/67) had saliva cotinine concentrations above the cut point. Exclusive current cigarette users were more likely to be classified discordantly by questionnaire and cotinine test compared to snus users (odds ratio 3.2, 95% confidence interval 1.2 to 8.6).

CONCLUSION

This study confirms the reliability of adolescents' self reported tobacco use. In a context of low exposure to environmental tobacco smoke a cut off for saliva cotinine of 5 ng/ml reliably discriminated tobacco users from non-users. Irregular use of tobacco in this age group probably explains the discrepancy between self reported use and cotinine concentrations.

Smoking mothers and snuffing fathers: behavioural influences on youth tobacco use in a Swedish cohort

OBJECTIVE

To analyse the influences of parental use of cigarettes and snus (the Swedish variety of smokeless tobacco) on offspring's behaviour.

DESIGN

Prospective cohort study.

SETTING

The Stockholm County of Sweden.

SUBJECTS

2232 adolescents recruited in the fifth grade (mean age 11.6 years) with follow up in the eighth grade.

MAIN OUTCOME MEASURES

Self reported tobacco use (ever and current use of cigarettes and/or snus) in the eighth grade.

RESULTS

Parents' tobacco use was associated with adolescents' current use of cigarettes and snus (odds ratio (OR) 2.7, 95% confidence interval (CI) 1.8 to 3.9 if both parents used tobacco v neither parent). Mother's cigarette smoking was associated with adolescents' current exclusive smoking (OR 2.4, 95% CI 1.6 to 3.6). Father's use of snus was associated with current exclusive use of snus among boys (OR 3.0, 95% CI 1.4 to 6.4), but not with current cigarette use. The overall prevalence of current smoking was lower among children whose fathers used snus than among those whose fathers smoked.

CONCLUSIONS

Parental smoking, especially maternal smoking, enhances the risk of tobacco experimentation in youths, as does paternal use of smokeless tobacco. However, the transition to regular cigarette smoking is not likely to be affected by paternal use of smokeless tobacco. Contextual factors, in particular declining smoking trends and negative social acceptance of smoking, can explain most of these findings.

Early gender differences in adolescent tobacco use--the experience of a Swedish cohort

BACKGROUND

In Sweden, the prevalence of tobacco use in the youth population differs by product and gender, but there are no longitudinal studies of gender differences in the uptake of smoking and use of oral snuff (OS).

METHODS

A prospective cohort study ongoing in the County of Stockholm, encompassing 3,019 children recruited in 1997 in the fifth grade of compulsory school, of whom 96% were followed-up in the sixth grade.

RESULTS

At baseline, 22% of the boys and 15% of the girls had ever smoked, respectively 8% and 3% had ever used oral moist snuff. One year later, the overall smoking prevalence had markedly increased, as did the transition to more advanced stages of smoking, especially among girls. Among boys who at baseline had only used oral snuff, 41% had also smoked cigarettes at follow-up. Lack of a firm intention to abstain from tobacco use was strongly associated with onset of experimentation within one year, particularly among boys.

CONCLUSIONS

Tobacco uptake in pre-adolescence differs between genders, with an earlier initiation among boys and a more rapid transition to regular smoking among girls. In most cases, experimentation with oral snuff among boys marks the transition to cigarette smoking.

Between harm and dangers. Oral snuff use, cigarette smoking and problem behaviours in a survey of Swedish male adolescents

BACKGROUND

The prevalence of smokeless tobacco use (moist snuff) in Sweden is among the highest world-wide, and snuff is gaining popularity as a less harmful alternative to cigarettes.

METHODS

Patterns of current tobacco use and indicators of behavioural problems were analysed in a sample of 6287 boys participating in a census survey among 9th graders in Stockholm County, Sweden.

RESULTS

Among participants reporting current use of oral snuff (OS) the majority (71%) also smoked cigarettes. The prevalence of daily smoking was significantly higher in this group than among exclusive smokers. Conditionally on smoking behaviour, the likelihood of being a current user of OS was several times higher among boys who had ever been drunk (adjusted odds ratio = 9.64, 95% confidence interval: 7.32-12.94) or experimented with illicit drugs (adjusted odds ratio = 2.39, 95% confidence interval: 1.99-2.87), compared with those who did not. OS use was also significantly associated to other problem behaviours such as drinking and driving, unsafe sex, and school truancy. The same pattern of associations was present when the analyses were restricted to tobacco users.

CONCLUSIONS

Smokeless tobacco use in adolescence does not substitute cigarette smoking and can be an indicator of a drug- and risk-seeking lifestyle. The availability of smokeless tobacco might thus increase the potential for nicotine addiction in some vulnerable subgroups of young males.

A pooled analysis of case-control studies of thyroid cancer. VI. Fish and shellfish consumption

OBJECTIVE

To better understand the role of fish and shellfish on thyroid cancer risk, we systematically re-analyzed the original data from 13 case-control studies conducted in the US, Japan, China, and Europe.

METHODS

A total of 2497 cases (2023 women, 474 men) and 4337 controls (3268 women, 1069 men) were considered. Odds ratio (OR) and corresponding 95% confidence interval (CI) were estimated for each study by logistic regression models, conditioned on age and sex, and adjusted for history of goiter, thyroid nodules or adenomas, and radiation. Combined ORs were computed as the weighted average of the estimates from each study.

RESULTS

The ORs for the highest level of total fish consumption (three or more times per week) as compared to the lowest one (less than once per week) was above unity in Hawaii, Connecticut, Japan, Norway, Tromsø, and Vaud. Conversely, the ORs for the studies in Los Angeles. Shanghai, southeastern Sweden, Uppsala, northern Sweden, northern Italy, and Athens were below one. The pattern of risk for salt water fish and shellfish was not substantially different from that of total fish. Fish was not associated with thyroid cancer risk in all studies combined (OR = 0.99, 95% CI 0.85-1.2 for moderate, and OR=0.88, 95% CI 0.71-1.1 for high total fish consumption), but there was a suggestion of a protective effect in endemic goiter areas (OR = 0.65, 95% CI 0.48-0.88).

CONCLUSION

This combined analysis indicates that relatively elevated fish consumption does not appreciably increase thyroid cancer risk, and may have a favorable influence in areas where iodine deficiency is, or was, common.

Factors affecting reproducibility of dietary reports using food frequency questionnaires

OBJECTIVE

To study the reproducibility of a food frequency questionnaire used to assess past dietary habits.

DESIGN

Repeated retrospective assessment of dietary habits of a population sample.

SETTING

Uppsala-Orebro Health Care Region of Sweden.

SUBJECTS

One-hundred and four subjects participating as control subjects in a case-control study on thyroid cancer.

INTERVENTIONS

Between spring 1993 and spring 1994 a case-control study was conducted in the study area, in order to investigate risk factors for thyroid cancer-diet among others. The study subjects reported their consumption of selected foods with reference 1-5 y before, as well as dietary changes that occurred from adolescence to adult age. One year later 197 control persons were invited to provide a second report of the same food items. Of the invited subjects 104 agreed to participate.

RESULTS

The median Spearman rank correlation coefficient between the first and second assessment was 0.58 for food consumption and 0. 56 for nutrients intake. Correlation between the two assessments varied greatly between food items, ranging from -0.03 to 0.83. The correlation was positively related to the frequency and negatively related to the skewness of consumption. The recall of dietary changes from adolescence had a median correlation coefficient of 0. 38 (range 0.19-0.69). There were hints of a higher reproducibility of dietary reports among men and among highly educated subjects (more than 11 y of education), but these differences were statistically significant only for recall of adolescent diet. Reproducibility of nutrients intake was also significantly higher among men than among women, as well as among subjects older than 45 y.

CONCLUSIONS

The reproducibility of dietary reports was satisfactory. Among factors affecting reproducibility, frequency and homogeneity of consumption in the source population are presumably the most important. Age, sex and education modify the inter-subject reproducibility of past diet. Based on reproducibility of a semi-quantitative index, the recall of adolescent diet probably has a low validity. European Journal of Clinical Nutrition (2000) 54, 658-664.

Diet-associated risks of disease and self-reported food consumption: how shall we treat partial nonresponse in a food frequency questionnaire?

Using data from a population-based case-control study on thyroid cancer, we studied two approaches of handling missing answers in a food frequency questionnaire when estimating food consumption and nutrient intakes. We analyzed the dietary reports of 165 cases and 248 control subjects. In the first approach, the omitted food items were considered as "null consumption." In the second approach, the missing answers were replaced with the median frequencies for subjects in the corresponding outcome category actually answering that specific food item. The results showed marginal differences between the two methods. In addition, the null consumption assumption was validated by means of complementary telephone interviews with a subsample of subjects who provided incomplete reports. Overall, the originally omitted answers actually corresponded to very rare consumption for 54.2% of cancer patients and for 54.7% of controls. However, this "true" proportion of null consumption varied greatly between different food items (range 0-96%) and between food groups (range 14-82%). To interpret the omitted self-reports of food consumption as indication of "zero consumption" is quite reasonable when the investigation does not focus on dietary items widely consumed in the source population.

A pooled analysis of thyroid cancer studies. V. Anthropometric factors

OBJECTIVE

To assess the relation between anthropometric factors and thyroid cancer risk in a pooled analysis of individual data from 12 case-control studies conducted in the US, Japan, China and Europe.

METHODS

2056 female and 417 male cases, 3358 female and 965 male controls were considered. Odds ratios (OR) were derived from logistic regression, conditioning on age, A-bomb exposure (Japan) and study, and adjusting for radiotherapy.

RESULTS

Compared to the lowest tertile of height, the pooled OR was 1.2 for females for the highest one, and 1.5 for males, and trends in risk were significant. With reference to weight at diagnosis, the OR for females was 1.2 for the highest tertile, and the trend in risk was significant, whereas no association was observed in males. Body mass index (BMI) at diagnosis was directly related to thyroid cancer risk in females (OR = 1.2 for the highest tertile), but not in males. No consistent pattern of risk emerged with BMI during the late teens. Most of the associations were observed both for papillary and follicular cancers, and in all age groups. However, significant heterogeneity was observed across studies.

CONCLUSIONS

Height and weight at diagnosis are moderately related to thyroid cancer risk.

Incidence of thyroid cancer in Scandinavia following fallout from atomic bomb testing: an analysis of birth cohorts

OBJECTIVES

The occurrence relation between radioactive fallout from nuclear testing at Novaja Semlja in north-west Russia and the incidence of thyroid cancer in Norway and Sweden was studied following a birth cohort approach.

METHODS

Birth cohorts with presumably different levels of exposure were identified according to calendar year of atomic tests and previous Norwegian estimates of the population dose (born 1947-1950 received low exposure in late childhood, born 1951-1962 received the highest exposure in early childhood, born 1963-1970 were not exposed). For each one-year birth cohort the incidence rates were calculated, with denominators based on exact population figures for each year of follow-up.

RESULTS

In a stratified analysis, the relative risk for the highest exposed cohorts born 1951-1962, compared to those not exposed born 1963-1970, was found to decrease with increasing age from a borderline significant relative risk (RR) of 1.7 (95 percent confidence interval, 95% CI: 1.0-3.0) for children in the age-group 7-14 years to no excess risk among those 20-24 years of age (RR: 0.9; 95% CI: 0.7-1.2). The mean age at diagnosis of thyroid cancer in the age-group 7 14 years was lowest in the birth cohorts with the highest exposure. The Poisson regression analysis showed essentially the same results, with an improved fit when adding an interaction term between age and birth-cohort to a basic model with age, gender, birth-cohort and country.

CONCLUSION

These results are compatible with an increased risk of thyroid cancer during childhood and adolescence for subjects exposed to radioactive fallout early in life. Alternative explanations for the pattern of incidence are discussed.

A pooled analysis of case-control studies of thyroid cancer. I. Methods

OBJECTIVE

Because the etiology of thyroid cancer is not well described, we conducted a pooled analysis of all published case-control studies, as well as two identified unpublished studies. This paper describes the major characteristics of the 14 studies included in the analysis, as well as the statistical methods employed. Four studies were conducted in the United States (1 each in Washington State, California, Connecticut and Hawaii), 8 in Europe (3 in Sweden, 2 in Norway, 1 in Switzerland, 1 in Italy and 1 in Greece), and 2 in Asia (1 in China and 1 in Japan).

METHODS

The original datasets were obtained and restructured in a uniform format. Data on socio-demographic characteristics, anthropometric measures, smoking and alcohol consumption, history of benign thyroid diseases and of other selected medical conditions and treatments, family history of cancer and of benign thyroid conditions, occupation, residence in endemic goitre areas, and dietary habits were analyzed. For women, we also analyzed menstrual and reproductive factors and use of female hormones. Radiotherapy and, in Japan, exposure to the A-bombs were considered as potential confounding factors.

RESULTS

A total of 2,725 cases (2,247 females and 478 males) and 4,776 controls (3,699 females and 1,077 males) were included in this study. Of the cases, 79% were classified as papillary thyroid carcinomas, 14% as follicular, 2% medullary, 1% anaplastic, 1% other histologies, and 3% histological type unknown. Each of the datasets was checked for outliers and consistency. Data were analysed separately by study center, gender, and the two major histologic types (papillary, follicular). Frequency tables and simple statistics were computed for each variable under study. Conditional logistic regression was used to compute odds ratios. For matched studies, the original matching was preserved, whereas, for unmatched ones, five-year age groups were used for matching. Study-specific analyses were computed, and then the data from all the studies were pooled conditioning on study. Heterogeneity between studies, geographic areas and study designs was assessed, and the modifying effect of age was also evaluated.

A pooled analysis of case-control studies of thyroid cancer. III. Oral contraceptives, menopausal replacement therapy and other female hormones

OBJECTIVE

The relations between oral contraceptives (OC), hormone replacement therapy (HRT) for menopause, and other female hormone use and thyroid cancer risk was analyzed using the original data from 13 studies from North America, Asia and Europe.

METHODS

Based on 2,132 cases and 3,301 controls, odds ratios (OR) and the corresponding 95% confidence intervals (CI) were obtained by conditional regression models, conditioning on study and age at diagnosis, and adjusting for age, radiation exposure and parity.

RESULTS

Overall, 808 (38%) cases versus 1,290 (39%) controls had ever used OCs, corresponding to an OR of 1.2 (95% CI 1.0 to 1.4). There was no relation with duration of use, age at first use, or use before first birth. The OR was significantly increased for current OC users (OR = 1.5, 95% 1.0 to 2.1), but declined with increasing time since stopping (OR = 1.1 for > 10 years since stopping). The association was stronger for papillary cancers (OR = 1.6 for current users) than for other histologic types. No significant heterogeneity was observed across studies or geographic areas. Eight studies had data on HRT, for a total of 1,305 cases and 2,300 controls: 110 (8%) cases and 205 (9%) controls reported ever using HRT (OR = 0.8; 95% CI 0.6 to 1.1). The ORs were 1.6 (95% to 0.9 to 2.9) for use of fertility drugs, and 1.5 (95% CI 1.1 to 2.1) for lactation suppression treatment.

CONCLUSIONS

The studies considered in these analyses include most of the epidemiological data on the role of exogenous hormone use in the etiology of thyroid cancer, and they provide reassuring evidence on the absence of an association of practical relevance. The moderate excess risk in current OC users, if not due to increased surveillance for thyroid masses among OC users, is similar to that described for breast cancer, and would imply a role of female hormones on thyroid cancer promotion. There was no indication of increased thyroid cancer risk 10 or more years after discontinuing OC use.

Diet and the risk of papillary and follicular thyroid carcinoma: a population-based case-control study in Sweden and Norway

A population-based case-control study was conducted in two regions of Sweden and Norway to investigate the association between dietary habits and the risk of thyroid cancer. The consumption of selected foods was reported in a self-completed food-frequency questionnaire by 246 cases with histologically confirmed papillary (n = 209) and follicular (n = 37) thyroid carcinoma, and 440 age- and gender-matched controls. Odds ratios (OR) and their 95 percent confidence interval (CI) were calculated as estimates of the relative risk using conditional logistic regression. High consumption of butter (OR = 1.6, CI = 1.1-2.5) and cheese (OR = 1.5, CI = 1.0-2.4) was associated with increased risks. Residence in areas of endemic goiter in Sweden was associated with an elevated risk, especially among women (OR = 2.5, CI = 1.3-4.9). High consumption of cruciferous vegetables was associated with increased risk only in persons who ever lived in such areas. A decreased risk was associated with consumption of iodized salt in northern Norway, and with use of iodized salt during adolescence among women (OR = 0.6, CI = 0.6-1.0). The results of this study suggest a role of diet and environment in the risk of thyroid cancer.

Parental cancer and risk of papillary and follicular thyroid carcinoma

In a population-based case-control study in the Uppsala-Orebro Health Care Region of Sweden, the histories of cancer among parents of 517 histologically confirmed cases of papillary and follicular carcinoma and of a similar number of sex- and age-matched controls were compared. The parental history of cancer was compiled through information from death certificates and from the nationwide Cancer Register. The incidence of malignancies in a cohort of parents of cases of thyroid cancer was also compared with the incidence in the whole Swedish population. A maternal history of cancer was more common among women with follicular carcinoma than among their controls (OR 2.11, 95% CI 0.96-4.67). Parents of probands with papillary carcinoma had an increased risk of thyroid cancer (OR 4.25, 95% CI 1.16-10.89), and mothers of probands with follicular carcinoma had an increased risk of stomach cancer (OR 3.65, 95% CI 0.99-9.35) compared with the general population. Cancer of the lung, breast, and pancreas were less common than in the general population. Familial cases of thyroid cancer were not limited to the papillary type. An inheritable pattern of carcinogenesis is possible for certain differentiated non-medullary thyroid cancers, but shared environmental exposures may also explain the parent-child associations of cancer in this study.

Reproductive history and cigarette smoking as risk factors for thyroid cancer in women: a population-based case-control study

A population-based case-control study was conducted in Northern Norway and Central Sweden to investigate hormonal and reproductive factors and cigarette smoking as determinants of papillary and follicular thyroid carcinoma in women. Information on 191 histologically confirmed cases and 341 age-matched controls was included. No clear association was found with regard to the number of live births, number of pregnancies, a history of incomplete pregnancies, or the use of oral contraceptives or hormonal replacement therapy. However, an early first childbirth (before 20 years of age, or less than 5 years after menarche) was associated with an increased risk of thyroid cancer. There was an increased risk of thyroid cancer among women with a history of artificial menopause compared to those with a spontaneous menopause [odds ratio (OR), 2.52; 95% confidence interval (CI), 0.96-6.62], which was more pronounced for the papillary carcinoma and after adjustment for age at menopause and use of replacement therapy. Cigarette smokers had a decreased risk of borderline statistical significance compared to nonsmokers (OR, 0.69; 95% CI, 0.47-1.01), particularly among premenopausal women (OR, 0.60; 95% CI, 0.38-0.96). This negative association persisted after adjustment for parity, hormonal treatments, and education. Women who started smoking before the age of 15 experienced a marked reduction in risk (OR, 0.38%; 95% CI, 0.18-0.80¿). Moreover, there was a suggestion of a dose-response effect with the amount of cigarettes smoked daily and with duration of the habit. Both the increased risk of artificial menopause and the negative association with smoking are compatible with a relation between levels of estrogens and thyroid cancer among women.

Medical diagnostic x rays and thyroid cancer

BACKGROUND

Diagnostic x rays are the largest man-made source of exposure to ionizing radiation for the general population. Whether there are meaningful cancer risks associated with such exposures is unclear. Most previous case-control studies have relied on recalled histories of x rays, and there is concern that completeness and accuracy of recall might differ between cancer case and control subjects.

PURPOSE

The present study used information recorded prospectively in hospital charts to address the relationship between medical diagnostic x rays and risk of thyroid cancer.

METHODS

The Swedish Cancer Registry and the Uppsala-Orebro Regional Cancer Registry were used to identify persons with papillary or follicular thyroid cancer diagnosed from January 1, 1980, through December 31, 1992, among residents of the Uppsala Health Care Region. After histopathologic review, there were 484 such case subjects available for study. An equal number of age-, sex-, and county of residence-matched control subjects from the general population were randomly selected on the basis of the Swedish Registry of the Total Population. Lifetime residential histories were compiled, and radiology records were searched at all Swedish hospital serving regions where study subjects ever maintained an official residence. Approximate radiation doses to the thyroid gland for specific types of x-ray examinations were assigned on the basis of mean values of measurements made in Sweden in 1973-1975 and in the United States in 1970. Odds ratios were used to evaluate the association between diagnostic radiography and risk of thyroid cancer.

RESULTS

A total of 3853 medical diagnostic x rays were ascertained among thyroid cancer case subjects and 4039 among the matched control subjects. There were no tendency for case subjects to have had more of the types of x-ray procedure associated with higher radiation dose to the thyroid gland (i.e., those involving the head or neck area). This finding was true even when analysis was restricted to x rays occurring before 1960, when doses likely were higher than in more recent years, and for examinations occurring in childhood and adolescence, when susceptibility to radiation-induced thyroid cancer is greatest. The relative risk of thyroid cancer was not significantly associated with estimated cumulative dose to the thyroid gland from diagnostic x rays (two-sided P for trend = .80).

CONCLUSION

These data indicate that the risk of thyroid cancer due to medical diagnostic x rays, if any, is very small.

Is residence in areas of endemic goiter a risk factor for thyroid cancer?

The association between an indicator of iodine deficiency and differentiated thyroid cancer has been investigated in a population-based case-control study. This included all incident cases (N = 484) of papillary and follicular thyroid cancer diagnosed during the years 1980-1992 in a Swedish Health Care Region among residents born in Sweden, and as many individually matched controls. Cases were included after a uniform review of their histopathological specimens. Residence in areas where goiter had been severely endemic in the 1930s was used as exposure indicator. Odds ratios (OR) and 95% confidence intervals as estimates of relative risk were calculated as a measure of association using logistic regression. A trend toward an association was found with a duration of residence in goiter areas between 21 and 40 years, most prominent among follicular cancer cases and in the group diagnosed at age > or = 50 years compared to not exposed. Exposure for the first time during adolescence (between 11 and 20 years) was associated with an increased risk of papillary cancer. This was especially evident among women, both when compared to not exposed and to those exposed during the first year of life; the association was strengthened after adjustment for duration of residence. These findings support the hypothesis of distinct causation patterns from iodine deficiency to the 2 most common histological types of thyroid cancer.

Parity and risk of thyroid cancer: a nested case-control study of a nationwide Swedish cohort

The association between parity and risk of thyroid cancer was examined in a case-control study nested within a cohort of Swedish women born 1925-60. A total of 1,409 cases of thyroid cancer were compared with 7,019 age-matched controls. Odds ratios (OR) and 95 percent confidence intervals (CI) were calculated as estimates of relative risk. A weak association was found between parity and risk of thyroid cancer (OR for ever-parous women cf nulliparous was 1.1, CI = 1.0-1.3). For the subset of papillary cancers, there was a significantly increased risk (OR for ever-parous cf nulliparous = 1.3, CI = 1.0-1.6), and among women diagnosed at the age of 50 or older, there was a positive linear trend with increasing number of livebirths. Women during the first year after a livebirth had an increased risk of thyroid cancer compared with women who delivered 10 or more years before; this association was most prominent among uniparous women (OR = 2.5, CI = 1.1-5.9). An increased risk was also apparent for age over 20 years at livebirth (among uniparous women) and age over 25 years at last livebirth (among multiparous women). A negligible effect of parity on thyroid cancer risk was seen, but each livebirth may have a short-term and age-dependent promoting effect.

Leprosy in Italy

A descriptive epidemiological study on the present prevalence of leprosy in Italy is presented. Cases are identified as notified to the Special Leprosy Section at the Italian Ministry of Health. Clinical cases are defined. In addition, sex and professional breakdowns are provided. Cases of the disease are identified as either imported or indigenous. Geographical distribution, according to importation status, is offered: no Italian region is free from leprosy. Incidence curves from 1920 are given, showing the continuous decline in the incidence of the disease. Possible applications of effective eradication programs are discussed.