Adolescents who show signs of alcohol dependence are more likely to develop depression by their mid-20s, according to a new study led by UCL (University College London) and University of Bristol researchers.

Drinking large amounts of alcohol regularly, but with no signs of dependency, did not predict depression risk, according to the findings published in The Lancet Psychiatry.

Co-lead author Dr. Gemma Lewis (UCL Psychiatry) said, "By using a large, longitudinal dataset, we have found evidence that problematic drinking patterns in late adolescence may increase the risk of developing depression years later."

"Problematic drinking patterns could be a warning sign of future mental health problems, so helping young people to avoid problematic alcohol use could have long-term benefits to their mental health."

The study involved 3,902 people who are part of the Children of the 90s birth cohort study (Avon Longitudinal Study of Parents and Children—ALSPAC), a longitudinal cohort of parents and their children born in the southwest of England in 1991 and 1992, who have been surveyed at regular intervals.

This paper looked at the association between alcohol consumption and signs of problematic drinking, or dependence, at age 18, and depression six years later at age 24.

Alcohol dependence signs include an inability to stop drinking, failure to meet normal expectations due to drinking, and feeling a need to drink after a heavy session, as well as harmful effects such as drink-related memory loss.

The researchers found that people who appeared to be dependent on alcohol at age 18 (or at any age from 17 to 22) were more likely than their peers to have depression at age 24. Those with a score of zero on the alcohol dependence scale at age 18 face an 11% probability of depression by age 24, compared to 15% for those with a score of one on the scale (an increase from zero to one on the alcohol dependency scale represents a 28% increase in the probability of not being able to stop drinking once started and a 33% increase in the probability of failing to do what was normally expected of you).

This relationship remained after they adjusted for potential confounding factors such as substance use and depressive symptoms at age 16, suggesting that there may be a causal relationship between alcohol dependence and subsequent depression that is not explained by poor overall mental health in adolescence.

The researchers found that consumption levels alone were not associated with an increased risk of depression, which they say may be partly due to the fact that drinking in late adolescence is often tied with social contact and reflects social norms.

Co-lead author Dr. Gemma Hammerton (University of Bristol) said, "While we found that alcohol consumption alone did not appear to increase the probability of depression, heavy drinking can be a precursor to dependence, and can have harmful physical health impacts in the longer term as well. High frequency and quantity of alcohol consumption therefore remain important as targets to prevent or reduce during adolescence."

"Public health interventions to prevent depression could target problematic alcohol use (such as if alcohol is having a negative impact on a person's personal relationships or responsibilities), which is likely to occur before dependence, and involve high frequency and quantity of consumption."

Mark Leyshon, Senior Research & Policy Manager at Alcohol Change UK, said, "Alcohol consumption among 18 to 24-year-olds has been falling for some time. However, there remains a significant number of young people who use alcohol in a harmful way. There were over 40,000 alcohol-related hospital admissions among under 24s in 2019, and more than a quarter of these were for mental and behavioral disorders as a result of alcohol. The findings from this new study reinforce the importance of protecting young people from alcohol harm, through early intervention and proper funding of youth addictions services so that the right support and treatment is there for everyone who needs it."

The findings align with the results of another recent UCL-led study in adults, which found that problematic alcohol use—but not level of consumption—is associated with increased odds of suicide attempt or self-harm.