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Background and aims: Research on adolescent predictors of later alcohol misuse is typically conducted on samples of singletons, and associations may be confounded by between‐family differences. To address potential confounding, we applied a co‐twin comparison design to evaluate whether differences between co‐twins in a wide array of adolescent risk factors predicted differences in young adult alcohol misuse. Design Longitudinal study in which associations between characteristics of the sample as adolescents were used to predict young adult alcohol misuse in individual‐level analyses and co‐twin comparisons. Setting: Finland. Participants: A total of 3402 individuals (1435 complete twin pairs; 36% monozygotic; 57% female) from the FinnTwin12 study. Measurements The young adult alcohol misuse outcome was a composite score of alcohol use and intoxication frequency. Adolescent predictors included factor scores representing academic performance, substance use, externalizing problems, internalizing problems, peer environment, physical health and relationship with parents; and single measures tapping alcohol expectancies, life events and pubertal development. Findings In individual‐level analyses, individuals with higher adolescent substance use, externalizing problems, time with friends, peer deviance, sports involvement, sleeping difficulties, parental discipline, positive alcohol expectancies and difficulty of life events reported higher alcohol misuse in young adulthood (Ps < 0.019, R2 = 0.0003–0.0310%). Conversely, those with higher adolescent internalizing problems, parent–child relationship quality and time with parents reported lower alcohol misuse (Ps < 0021, R2 = 0.0018–0.0093%). The associations with adolescent substance use and alcohol expectancies remained significant in co‐twin comparisons (Ps < 0.049, R2 = 0.0019–0.0314%). Further, academic performance emerged as a significant predictor, such that individuals with higher grades compared with their co‐twin reported higher young adult alcohol misuse (Ps < 0.029, R2 = 0.0449–0.0533%). Conclusions: Adolescent substance use, positive alcohol expectancies and higher academic performance appear to be robust predictors of later alcohol misuse. [ABSTRACT FROM AUTHOR]

Aims To determine (1) the prospective associations of conduct problems during early adolescence with tobacco, alcohol and cannabis use in young adulthood and (2) to what extent these associations are due to overlapping genetic versus environmental influences. Design A prospective twin study using biometric twin modelling. Setting Finland. Participants A total of 1847 Finnish twins (943 males and 904 females) were interviewed in early adolescence, 73% of whom ( n = 1353, 640 males and 713 females) were retained in young adulthood. Measurements Symptom counts of conduct disorder (CD) criteria were obtained from a semi-structured clinical interview in early adolescence [age 14-15 years, mean = 14.2, standard deviation (SD) = 0.15]. Frequency of alcohol, tobacco and cannabis use was obtained from a semi-structured clinical interview in young adulthood (age 19.9-26.6 years, mean = 22.4, SD = 0.7). Findings We found modest to moderate phenotypical correlations ( r = 0.16-0.35) between early adolescent CD symptoms and substance use in young adulthood. In males, the phenotypical correlations of CD symptoms with all three substance use variables are explained largely by overlapping genetic influences. In females, overlapping shared environmental influences predominantly explain the phenotypical correlation between CD symptoms and tobacco and cannabis use. Conclusions Conduct disorder symptoms in early adolescence appear to moderately predict substance use in early adulthood. In males, genetic influences seem to be most important in explaining the relationship between conduct disorder symptoms and substance use whereas in females, shared environmental influences seem to be most important. [ABSTRACT FROM AUTHOR]

Aims To control for familial confounds, we studied the association between adolescent physical activity and later smoking in twin siblings discordant for their baseline physical activity. Design and measurements In this prospective population-based twin study, we asked whether persistent physical activity/inactivity in adolescence (assessed at 16, 17 and 18.5 years) predicted questionnaire-reported daily smoking at ages 22–27. Twins who, on the three baseline questionnaires, consistently reported frequent leisure physical activity (more than three times weekly) were classified as persistent exercisers, those who exercised less than three times monthly were called persistently inactive, others were occasional exercisers. Setting Finland. Participants A total of 4240 individuals, including 1870 twin pairs. Findings In analyses of individual twins, compared to persistent activity, persistent physical inactivity predicted increased risk of daily smoking (age- and sex-adjusted odds ratio 5.53, 95% confidence interval 3.88–7.88, P < 0.001). The risk remained elevated even after excluding all those who had smoked 50 cigarettes or more life-time at baseline and adjusted for educational level in adolescence. In within-pair analyses compared to the active members of discordant twin pairs, the physically inactive co-twins had increased risk of future daily smoking (sex-adjusted odds ratio 3.39, 95% confidence interval 1.56–7.39, P = 0.002). Conclusions Persistent physical inactivity in adolescence relates to adult smoking, even after familial factors are taken into account. [ABSTRACT FROM AUTHOR]

To examine how adolescents’ inattentive behaviour, together with parental smoking patterns, predicts smoking initiation by age 14. A prospective, longitudinal study: baseline at ages 11–12, follow-up at age 14. A population-based sample of Finnish twins, born 1983–1987, with parents and classroom teachers as additional informants. Two groups were formed, allocating the co-twins of each family into separate groups: the study sample and a replication sample. Twin individuals ( n = 4552), aged 11–12 at baseline and 14 (average 14.04 years) at follow-up. At baseline, inattentiveness was assessed with the Multidimensional Peer Nomination Inventory (MPNI, Teacher Form) and parental smoking with individual questionnaires completed by each twins’ parents; at the age 14 follow-up, adolescent smoking was assessed with a self-report questionnaire. At age 14, 57% reported never having smoked, 34% had experimented with cigarettes and 9% were current smokers. Inattentiveness and parental smoking additively predicted both experimental and current smoking in adolescence. The effects were independent of each other. The risk related to inattentiveness itself is high, but in combination with the effects of parental smoking, the probability of current smoking can rise as high as 38%, compared with 5% without these two risk factors. For prevention purposes, parental commitment to non-smoking should be emphasized. [ABSTRACT FROM AUTHOR]

Background and Aims Design Participants/Setting Measurements Findings Conclusions Studies on adolescent alcohol use and cognition are often unable to separate the potential causal effects of alcohol use on cognition from shared etiological influences, including genetic influences or other substance use comorbidities also known to be associated with cognition, such as nicotine use. The present study aimed to fill this gap and clarify the relationship between adolescent alcohol use and young adult cognition by accounting for both measured and unmeasured confounders.A random effects model accounting for nesting in families was used to control for measured confounders. Next, co‐twin comparisons were conducted within the full sample and in monozygotic twin pairs (MZ) to control for unmeasured genetic and environmental confounders shared by co‐twins.Participants were 812 individuals (58.6% female, 361 complete pairs, 146 MZ pairs) from the longitudinal FinnTwin12 study in Finland.Adolescent alcohol use was indexed with measures of frequency of use and intoxication averaged across ages 14 and 17. Cognitive outcomes were measured at average age 22 and included Trail Making Test, California Stroop test, Wechsler Adult Intelligence subtests (Vocabulary, Block Design, Digit Symbol), Digit Span subtest of Wechsler Memory Scale, Mental Rotation Test and Object Location Memory test. Covariates included sex, parental education, general cognitive ability, current alcohol use and nicotine use.Greater frequency of alcohol use and frequency of intoxication across adolescence was associated with decreased vocabulary scores in the co‐twin control [freq: stnd beta = −0.12, 95% confidence interval (CI) = −0.234, −0.013] and MZ only co‐twin control models (freq: stnd beta = −0.305, 95% CI = –0.523, −0.087; intox: stnd beta = −0.301, 95% CI = ‐0.528, −0.074).In Finland, there appears to be little evidence that adolescent alcohol use causes cognitive deficits in young adulthood, except modest evidence for association of higher adolescent alcohol use with lower young adult vocabulary scores. [ABSTRACT FROM AUTHOR]