New research points to the effects someone’s risky behavior in their 20s has on their cognitive health in their 50s and beyond.
University of Michigan researchers followed people from age 18 through their 50s and 60s, tracking people with ‘triple threat’ habits – smoking daily, binge drinking or using cannabis frequently.
A daily smoking habit in young adulthood predicted worse self-reported memory by age 50, regardless of whether the person had quit by age 35.
For binge drinking and cannabis, the harm to memory was indirect: heavy use in young adulthood raised the odds of developing a substance use disorder by midlife, and that disorder directly damaged cognitive health.
Dr Megan Patrick, principal investigator of the Monitoring the Future Panel Study, said: ‘Substance use has both acute and long-term effects on health and well-being. Poor memory is a common sign of early dementia.
‘Identifying the risk factors that can lead to dementia is crucial for the prevention and treatment of cognitive decline.’
Previous studies have linked midlife memory complaints to later dementia risk. The Michigan researchers did not diagnose cognitive decline.
Rather, they asked participants how they felt about their memory, then looked back at substance use decades earlier.
Alzheimer’s does not always begin with mild cognitive impairment (MCI). And most MCI never becomes Alzheimer’s — it can be caused by vascular issues, depression, medication or sleep disorders. Some people with MCI stay stable; a small percentage even improve (stock)
The study, published in the Journal of Aging and Health, used data from the Monitoring the Future (MTF) Longitudinal Panel Study.
While the study did not administer objective cognitive tests, such as memory or executive function exams, it used poor self-rated memory as a validated early indicator of cognitive decline.
Researchers asked 16,000 Americans from age 18 into their 50s and 60s a single question: ‘Would you say your memory is excellent, very good, good, fair, or poor?’ Anyone who answered ‘fair’ or ‘poor’ was considered to have poor self-rated memory.
Participants were surveyed repeatedly between the ages of 18 and 30, with each survey period covering roughly two years. At each wave, people reported how often they drank, smoked or used cannabis.
Researchers then counted how many of those waves a person engaged in heavy use, such as daily smoking, binge drinking or using cannabis 20 or more times a month.
Throughout the study, researchers tracked how many of those substance use waves occurred in participants’ lives.
By midlife, about one in 10 reported that their memory was ‘fair’ or ‘poor.’
In young adulthood, participants averaged two waves of binge drinking, defined as having five or more drinks in a row in the past two weeks.
They averaged just over one wave of daily smoking and less than one wave of heavy alcohol use — drinking 20 or more days a month — or frequent cannabis use, which involves using 20 or more days a month.
Alcohol use disorder, meanwhile, is defined as meeting two or more diagnostic criteria for problem drinking over the past five years, including loss of control, cravings or continued use despite harm to oneself.
By age 35, more than a quarter of participants showed signs of alcohol use disorder, six percent had cannabis use disorder — meaning their use of marijuana had caused significant life problems or loss of control — and nine percent smoked a pack of cigarettes or more a day.
The numbers might look small at first glance, but what makes them significant is that these risks did not fade after a few years. They lasted decades.
A person who engaged in heavy alcohol use in their 20s was not just at slightly higher risk of memory problems in their 30s. Each wave of heavy drinking raised the odds by 13 percent, and that risk persisted 30 to 40 years later, when they reached their 50s and 60s.
The study found that for binge drinking in young adulthood, the link to poor memory disappeared once researchers accounted for whether someone had developed alcohol use disorder by age 35.
That suggests that people who binge drank in their 20s but stopped before midlife, and never developed a disorder, likely faced no lasting impact on their memory decades later.
However, for those whose heavy drinking, whether frequent or episodic, continued into their 30s and led to alcohol use disorder by age 35, the effect was significant.
The map, unrelated to the latest study from the University of Michigan, shows the percentages of Medicare enrollees (people 65 and up) who have dementia. The disease is most prevalent in the Southeastern US
People with alcohol use disorder at 35 were 32 percent more likely to report poor memory in late midlife compared to those who drank without disorder.
People who used cannabis frequently in young adulthood were more likely to report poor memory decades later — an eight percent increase in risk for each wave of heavy use. This was the first phase of the analysis.
But when researchers accounted for midlife cannabis use disorder, that link vanished, meaning young adult use itself wasn’t the direct cause. Rather, young adult users were more likely to develop the disorder, and that disorder caused the memory problems.
Heavy marijuana use in one’s 20s raised the odds of developing cannabis use disorder by age 35.
And those who developed the disorder were 36 percent more likely to report poor memory later in life compared to those who used cannabis without developing a disorder.
In other words, frequent cannabis use in young adulthood only mattered if it continued into midlife and became a disorder. If it did not, there was no lasting impact on memory.
Cigarettes were different.
People who smoked daily during more waves of young adulthood were significantly more likely to still be smoking later in life.
For each additional wave of daily smoking in their 20s, they were nearly twice as likely to be smoking a pack or more a day at 35.
But cigarettes diverged from alcohol and cannabis. Even after accounting for midlife smoking, each additional wave of daily smoking in young adulthood raised the odds of poor memory decades later by about five percent.
In other words, the damage from cigarettes appears to come from cumulative exposure in young adulthood itself, not from whether the habit continued into midlife. Quitting by age 35 did not erase the risk.
The human brain continues developing well into a person’s mid-20s, particularly in regions responsible for impulse control, decision-making and long-term planning —the functions needed for someone to recognize when a habit is becoming a problem.
During this window of heightened neuroplasticity, the brain is highly sensitive to rewards and more easily rewired by substances like alcohol, cannabis, and nicotine.
Occasional experimentation, over repeated exposure, strengthens neural pathways that reinforce compulsive use, making it harder to stop even as consequences mount.
Roughly 28 million Americans have alcohol use disorder, nearly 19 million have cannabis use disorder and approximately 29 million smoke cigarettes, making each condition a major public health threat.
An estimated seven million Americans, meanwhile, live with Alzheimer’s Disease.
That figure is slated to double by 2060, driven by the rapid aging of the baby boomer population as well as an overall rise in the number of Americans living into old age — the leading risk factor of the disease.
