Chronic alcohol and marijuana use during youth can compromise white-matter integrity

December 14, 2012

Chronic use of alcohol and marijuana during youth is associated with poorer neural structure, function, and metabolism, as well as worsened neurocognitive abilities into later adolescence and adulthood. This may be due to biological and psychosocial transitions occurring during adolescence that impart increased vulnerability to neurotoxic influences. A study of longitudinal changes in fiber tract integrity associated with adolescent alcohol and marijuana use during 1.5 years supports previous findings of reduced white-matter integrity in these youth.

Results will be published in a special online issue of Alcoholism: Clinical & Experimental Research and are currently available at Early View.

"Research has shown differences in the brains of teens who use alcohol and as compared to teens who do not use these drugs or report only very infrequent, minimal use," said Joanna Jacobus, postdoctoral fellow at the University of California, San Diego as well as corresponding author for the study. "Alcohol and marijuana may have a negative impact by altering important cellular communication in the , preventing development of new healthy cells, and/or causing inflammation, which can adversely impact healthy brain development in many ways. For example, the results can lead to changes in brain structure such as volume, and function such as activity."

"The areas of the brain that are composed mostly of connecting axons have been termed ',' since these areas appear white in color," added Duncan Clark, associate professor of psychiatry at the University of Pittsburgh Medical Center. "However, prior research has not clearly demonstrated that this white matter disorganization is caused by alcohol or marijuana use. In some studies where are studied only once, white matter disorganization may have been present prior to alcohol or marijuana use."

"The teen brain is continuing to develop, so many neural systems are not yet fully matured, as compared to adults' brains," said Jacobus. "Brain connections important for inhibiting risky behaviors are still forming, and some youth are more likely to choose immediate effects, such as alcohol or marijuana use, over long-term benefits."

Clark agreed. "Maturation of the brain during adolescence is thought to be the foundation for self-control," he said. "The developing adolescent brain, compared to the fully developed adult brain, is also probably more vulnerable to alcohol neurotoxicity. Adolescents are vulnerable to loss of control and, when this loss of control involves substance use, excessive or risky substance use can have adverse consequences."

For 18 months, the researchers followed 92 adolescents (63 males, 29 females), ages 16 to 20 years, divided into two groups: 41 with extensive alcohol and marijuana use histories by mid-adolescence, and 51 with consistently minimal if any substance use. Participants were part of an ongoing longitudinal study of substance use in adolescence with teens recruited from local schools from 2005 to 2007. Both groups received diffusion tensor imaging and detailed substance use assessments, along with toxicology screening, at baseline and 18-month follow-ups – 182 scans in all – as well as interim substance-use interviews every six months.

"We found evidence for poorer white matter tissue health in teens who engage in heavy alcohol and marijuana use compared to those who abstain," said Jacobus. She noted that white matter, the "information highway of the brain," allows for quick and efficient communication between brain regions. Compromised white matter can mean slower cognitive processing and poorer cognitive performance such as memory, attention, and decision-making.

"As to whether there were differences in these teens before they began using alcohol and marijuana is difficult to determine, but we found that increasing alcohol use over 1.5 years in late adolescence was related to a decline in white matter health 18 months later, supporting a negative effect of alcohol use on the brain despite potential pre-existing differences," Jacobus said.

"White matter organization was particularly compromised in an area called the superior longitudinal fasciculus," added Clark. "This is one of the major connection roadways in the brain. When the connections between brain areas are severely damaged, those areas of the brain cannot properly function. While the more subtle deficit shown here may impair functioning, the degree of deficit involved is not likely to be obvious in day-to day functioning. However, we are concerned that even these subtle deficits in brain microstructure may lead to diminished self-control."

"Our findings underscore that early initiation of and marijuana use can have negative implications on the brain" said Jacobus. "We hope this information can be communicated to teens to help them understand why drinking during adolescence is discouraged. In the future, biomarkers such as tissue health may help identify teens that are particularly vulnerable for engaging in riskier behaviors such as drinking."

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3.7 / 5 (6) Dec 14, 2012

You can remove one of the named substances from the equation and still note the same resulting effects.

Chronic use of the two substances should, therefore, be further broken into two additional study cohorts --alcohol users only, and marijuana users only-- and the outcomes with these two cohorts compared against each other, dual users, and a non-user control group.

Only then will it be possible to properly control for effects between the two substances and their "conjoint" use.

This is "research" searching for confirmation bias.

I could guarantee the exact same results in youthful populations of orange juice-drinking gas-huffers.

2 / 5 (8) Dec 15, 2012
Actually, cannabis appears to stimulate nerve growth and protect nerve sheaths, which is why it has been found effective treating patients suffering from MS and cerebral palsy. ... Which is not to say that teenagers shouldn't be confined to their rooms until their brains have matured (except for the ones we need for sports entertainment and military purposes, of course.)
2 / 5 (4) Dec 15, 2012
It indeed looks like the research was done for people using BOTH substances simultaneously. What purpose would it serve other than political if the results are not compared to heavy drinkers with no cannabis, or cannabis-only users.
1 / 5 (2) Dec 15, 2012
Cannabis plant can be used for phytoremediation of soils contaminated with cadmium. Accumulates in the cannabis leaves. Cadmium has a half life in the human of about 30 years. Minimum dose for txicity has been found lower than previously thought. Many other edible plants are efficient in accumulating cadmium. Cadmium is very pervasive in soils and waters (mussels, oysters etc.).
Cadmium is toxic to the white matter. Do you know what the cadmium content of the soil was on the hemp obtained? Some wines are contaminated with cadmium from grapes grown on contaminated land. Think about it.
1 / 5 (3) Dec 15, 2012
Accumulates in the leaves? Good thing most folk smoke the flowers, then...
Yeah, 2 substances, poor research. BAD SCIENCE! No new funding!
1 / 5 (3) Dec 17, 2012
"Chronic use of alcohol and marijuana during youth is associated with poorer neural structure, function, and metabolism"
I believe there may be a bit of a chicken-or-the-egg puzzle going on here. Does the use of mind-altering substances as a youth make one stupid, or vice-versa?

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