Adult Consequences of Late Adolescent Alcohol Consumption: A Systematic Review of Cohort Studies

In a systematic review of cohort studies of adolescent drinking and later outcomes, Jim McCambridge and colleagues show that although studies suggest links to worse adult physical and mental health and social consequences, existing evidence is of poor quality. Background: Although important to public policy, there have been no rigorous evidence syntheses of the long-term consequences of late adolescent drinking. Methods and Findings: This systematic review summarises evidence from general population cohort studies of drinking between 15–19 years old and any subsequent outcomes aged 20 or greater, with at least 3 years of follow-up study. Fifty-four studies were included, of which 35 were assessed to be vulnerable to bias and/or confounding. The principal findings are: (1) There is consistent evidence that higher alcohol consumption in late adolescence continues into adulthood and is also associated with alcohol problems including dependence; (2) Although a number of studies suggest links to adult physical and mental health and social consequences, existing evidence is of insufficient quality to warrant causal inferences at this stage. Conclusions: There is an urgent need for high quality long-term prospective cohort studies in order to better understand the public health burden that is consequent on late adolescent drinking, both in relation to adult drinking and more broadly. Reducing drinking during late adolescence is likely to be important for preventing long-term adverse consequences as well as protecting against more immediate harms. : Please see later in the article for the Editors' Summary Background: The effects of alcohol intoxication (drunkenness), dependence (habitual, compulsive, and long-term drinking), and the associated biochemical changes, have wide-ranging health and social consequences, some of which can be lethal. Worldwide, alcohol causes 2.5 million deaths (3.8% of total) and 69.4 million (4.5% of total) of disability-adjusted life years (DALYs). Unintentional injuries alone account for about one-third of the 2.5 million deaths, whereas neuro-psychiatric conditions account for almost 40%. There is also a causal relationship between alcohol consumption and more than 60 types of disease and injury; worldwide, alcohol is estimated to cause about 20%–30% cases of esophageal cancer, liver cancer, cirrhosis of the liver, homicide, epilepsy, and motor vehicle crashes. There is increasing evidence that, in addition to the volume of alcohol consumed, the pattern of drinking has an effect on health outcomes, with binge drinking found to be particularly harmful. As the majority of people who binge drink are teenagers, this group may be particularly vulnerable to the damaging health effects of alcohol, leading to global concern about the drinking trends and patterns among young people. Why Was This Study Done?: Although there have been many published cohort studies reporting the longer term harms associated with adolescent drinking, the strength of this evidence remains unclear, which has implications for the objectives of interventions. For example, if adolescent drinking does not cause later difficulties, early intervention on, and management of, the acute consequences of alcohol consumption, such as antisocial behaviour and unintentional injuries, may be the most appropriate community safety and public health responses. However, if there is a causal relationship, there needs to be an additional approach that addresses the cumulative harmful effects of alcohol. The researchers conducted this systematic review of cohort studies, as this method provides the strongest observational study design to evaluate evidence of causality. What Did the Researchers Do and Find?: The researchers conducted a comprehensive literature review to identify relevant studies that met their inclusion criteria, which were: (1) data collection from at least two points in time, at least 3 years apart, from the same cohort; (2) data collection regarding alcohol consumption between the ages of 15 and 19 years old; and (3) inclusion of a report of at least one quantitative measure of effect, such as an odds ratio, between alcohol involvement and any later outcome assessed at age 20 or greater. The majority of these studies were multiple reports from ten cohorts and approximately half were from the US. The researchers then evaluated the strength of causal inference possible in these studies by assessing whether all possible contributing factors(confounders) had been taken into account, identifying studies that had follow-up rates of 80% or greater, and which had sample sizes of 1,000 participants or more. What Do These Findings Mean?: The results of this study show that that the evidence-base on the long-term consequences of late adolescent drinking is not as extensive or compelling as it needs to be. The researchers stress that there is an urgent need for high quality long-term prospective cohort studies in order to better understand the public health burden associated with adolescent drinking in general and in relation to adult drinking. However, there is sufficient evidence to suggest that reducing drinking during late adolescence is likely to be important for preventing long-term adverse consequences as well as protecting against more immediate harmful consequences harms. Additional Information: Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1000413.