Early and risky adolescent alcohol use have each been associated with adult alcohol consumption. However, it remains unclear whether these behaviours independently predict later-life substance use when considered jointly, and research examining links with substances other than alcohol is limited. This study addresses these gaps by examining longitudinal associations between age at first alcohol and risky adolescent alcohol use, with alcohol, tobacco, cannabis and other drug use in early adulthood, and aims to identify critical periods for public health interventions. Growing Up in Ireland is a nationally representative cohort (recruited aged 9 [Wave 1], born 1997–1998). Survey-weighted logistic regression examined whether age at first alcoholic drink and risky alcohol use at age 17 (Alcohol Use Disorders Identification Test scores) independently predict high-risk alcohol (AUDIT > 15), tobacco, cannabis and other drug use at age 20. Models were adjusted for age, sex, academic ability, personality, psychological factors, socioeconomic status, familial, peer and neighbourhood substance use. The study included 4554 participants (49.8% female). Early alcohol use was common, with 27% reporting use aged 14 or younger. By age 20, 14% reported high-risk alcohol, 38% tobacco, 24% cannabis and 28% other drug use. Older age at first alcohol was associated with dose-response reductions in the odds of high-risk alcohol, tobacco, cannabis and other drug use at age 20, relative to those initiating alcohol at 14 or younger. Adolescents with high-risk alcohol use had double the odds of tobacco (adjusted odds ratio (aOR) 2.1, 95% confidence intervals (CI) 1.3–3.30) and other drug use (aOR 2.5, 95% CI 1.6–4.1) and an 11-fold increase in the odds of continued high-risk alcohol use (aOR 11.5, 95% CI 7.0–18.6) at age 20, relative to adolescents with low-risk alcohol use. Age at first alcohol and risky adolescent alcohol use independently predict substance use in early adulthood when considered jointly in extensively adjusted models. These findings highlight the continued urgent need for public health interventions that address factors associated with early alcohol use and support adolescents who use alcohol in a high-risk manner given their elevated risk of progression to more serious substance use as adults.

Many determinants of vitamin D status have been well-described, yet supplementation guidelines largely follow a one-size-for-all model and deficiency remains common. We hypothesised that accounting accurately for ultraviolet-B (UVB) radiation and considering interactions could advance understanding of vitamin D status. Asian, Black, and White participants from the UK Biobank cohort were included (N = 438,978). The Tropospheric Emission Monitoring Internet Service provided UVB data which we linked to participants' place of residence. UVB dose over 135 days prior to blood draw was weighted and added, yielding cumulative and weighted UVB (CW-D-UVB). The association between 25(OH)D and selected variables was assessed in multivariable linear regression models with and without interactions, stratified by ethnicity. Predictors were ranked using standardised β-coefficients. Median 25(OH)D differed by ethnicity (Asian: 25.4 nmol/L (10.2 ng/mL), Black: 30.6 nmol/L (12.2 ng/mL), White: 47.9 nmol/L (19.2 ng/mL), p-value < 0.001). CW-D-UVB was strongly associated with 25(OH)D in all ethnicities. It was the most important predictor in White (β_Asian = 0.15, β_Black = 0.20, β_White = 0.35), whereas supplementation was in Asian and Black participants (β_Asian = 0.30, β_Black = 0.24, β_White = 0.21). We identified statistically significant interactions between BMI:supplementation (all), CW-D-UVB:sex (Asian and White), and CW-D-UVB:age (Black and White), and in White population between CW-D-UVB and supplementation, BMI, and cholesterol. Vitamin D deficiency was widespread, particularly among non-White individuals. UVB was a strong predictor of 25(OH)D and the effect was modified by other factors. Findings suggest that accurately measured ambient-UVB radiation and interactions could improve 25(OH)D prediction models, and support personalised approaches to vitamin D optimisation.

Background: Research has demonstrated positive associations between adverse childhood experiences (ACEs) and substance use behaviours in young adults. However, many of these are based on cross-sectional data. The pathway between ACEs and substance misuse among emerging adults is also not fully understood and few studies have investigated potential mediating factors. Methods: We analysed data from the Child Cohort of the Growing Up in Ireland study, a nationally representative longitudinal sample of children recruited at 9 years of age (n = 4,729). Logistic regression was used to examine individual and cumulative ACE exposure relationships with substance use at age 20 years. Mediation analyses were used to assess whether parental and peer relationships and school engagement mediate ACE history associations with substance use behaviours. Results: ACE exposure relationships with current cannabis use, other illicit drug use and problematic drug use were observed. In particular, young adults who had experienced 2 ACEs or 3 + ACEs had an approximate twofold (OR=1.80, 95 % CI: 1.29, 2.51) and approximate three-fold (OR=2.94, 95 % CI: 2.06, 4.19) increased odds of problematic drug use, respectively, when compared to participants who had experienced no ACEs during the study period. Mediation analyses suggested that parent and peer attachment and liking school partially mediate relationships between ACEs and substance use behaviours. Conclusions: Children who have experienced ACEs are at higher risk of future substance use and problematic drug use. In supporting these children, identified mediators such as interpersonal relationships and school engagement may help guide selection of prevention interventions.

Nicotine product use (NPU; including combustible tobacco products and/or e-cigarettes) is changing rapidly worldwide. Aiming to inform an agile policy response, this study examined NPU trends, and associations with intentions and attempts to quit tobacco. Survey-weighted prevalences of NPU (tobacco and/or e-cigarette), tobacco, e-cigarette, and dual (tobacco and e-cigarette) use were estimated from 2015 to 2023 (excluding 2020 and 2021) using seven waves of the nationally representative Healthy Ireland survey (combined N = 52,167). Associations between sociodemographic factors and NPU, as well as between NPU and quit intentions and attempts, were examined using survey-weighted regression in the 2015 and 2023 waves. Between 2015 and 2023, decreases in NPU were non-significant (24·6% (1846/7502) to 22·9% (1688/7356), p_trend = 0·120), while tobacco use decreased (22·8% (1713/7502) to 17·7% (1303/7356), p_trend = 0·012), e-cigarette use increased (3·1% (230/7502) to 8·4% (614/7356), p_trend = 0·001) and dual use increased (1·3% (97/7502) to 3·1% (230/7356), p_trend = 0·006). Among those aged 15–24, NPU increased from 19·6% (214/1095) in 2015 to 30·0% (345/1149) in 2023. In 2015, dual use was strongly associated with higher odds of quit intentions and attempts to quit tobacco, compared to tobacco-only, but this was no longer the case in 2023. E-cigarette and dual use have more than doubled in Ireland, while tobacco declines have slowed. The most substantial changes occurred among 15–24-year-olds. Concurrently, the link between dual use and quit intentions and attempts attenuated. These findings underscore the need for stronger e-cigarette regulation and renewed policy efforts to achieve tobacco endgame in Ireland. None.

Despite growing concerns about trends in cocaine use, there is a shortage of longitudinal research that prospectively examines risk and protective factors associated with cocaine initiation and use in general youth populations. This study addresses this gap. Growing Up in Ireland is a nationally representative cohort. Individual, family, and socio-environmental exposures associated with incident past-year cocaine use at ages 17 (N = 5965) and 20 (n = 4549) were assessed with survey-weighted logistic regression using generalised estimating equations. Prevalent past-year cocaine use at 20 (N = 4679) was analysed using generalised estimating equations complemented by gradient-boosted decision trees and Shapley explanations. 221 (3.7%) self-reported cocaine use at 17 and 1072 (22.9%) at 20. Alcohol use at 14 or younger was associated with eight times the odds of cocaine use at 17 (aOR 8.0, 95% CI 1.7-37.3) and 19 times at 20 (aOR 19.2, 95% CI 8.6-43.2). Peer cannabis use was associated with 7 times the odds of cocaine use at 17 (aOR 7.3, 95% CI 2.9-18.3) and double at 20 (aOR 2.4, 95% CI 1.8-3.2). Growing up in a neighbourhood where substance use was common doubled the odds of cocaine use at 17 (aOR 2.4, 95% CI 1.3-4.4). Shapley explanations revealed individual-specific positive or negative impacts of exposures. Cocaine use among 20-year-olds in Ireland is higher than reported internationally, and increases sharply between the ages of 17 and 20, suggesting a need for interventions targeting this age group. However, associations with early adolescent factors suggest that early interventions may also be important.

Background: Adolescence is a pivotal life stage marked by educational advancement, entry into the workforce and formation of lasting relationships. Globally, adolescence is also the peak period during which individuals first engage in alcohol and/or drug consumption. This scoping review aimed to summarize existing longitudinal research on factors and outcomes related to adolescent substance use to identify gaps in existing evidence. Methods: A scoping review was conducted in accordance with the PRISMA extension for scoping reviews. A systematic literature search was conducted on PubMed. Additional studies were identified through hand-searching key reference lists and Google Scholar searches. A narrative synthesis was completed. Results: 123 studies were included; 12 reviews and 111 cohort studies. 60% of cohort studies originated from North America, 29% Europe, 7% Australia/New Zealand, 2% South America and 2% Asia. Factors consistently associated with increased risk of ASU include male sex, increasing age, externalizing disorders, adverse childhood experiences and peer or parental substance use. Few studies considered wider community or neighbourhood factors. Early initiation and higher frequency of adolescent drug use were predictive of later-life substance use patterns, education derailment, contact with the justice system and mental health disorders. Conclusions: The body of longitudinal evidence on adolescent substance use is rapidly expanding yet significant research gaps exist. Rising levels of cocaine use and its substantial health impacts motivate further research on all potentially important factors associated with cocaine use to guide interventions for prevention and treatment. Key messages: • There are important gaps in existing research on adolescent substance use. • These include neighbourhood influences and factors associated with initiation of illicit drugs other than cannabis.