Cannabis use — alongside schizophrenia, bipolar disorder, and alcohol consumption — can age the brain prematurely.
For what is thought to be the largest study of its kind, the researchers analyzed brain scans of 31,227 people aged 9 months–105 years.
In a paper that now features in the Journal of Alzheimer's Disease, they describe how they identified "patterns of aging" from the brain scans.
These were done using single photon emission computed tomography (SPECT) and came from people with psychiatric conditions such as attention deficit hyperactivity disorder (ADHD), schizophrenia, and bipolar disorder. They were all attending a psychiatric clinic that was based at several locations.
Each participant underwent two SPECT brain scans — one during a resting state, and another during completion of "a concentration task" — giving a total of 62,454 scans.
The scientists found that they could predict a person's age from the pattern of blood flow in their brain.
Brain circulation varied over lifespan
They observed that blood flow varied from childhood into older age throughout the lifespan. They also saw that brain aging was more visible in scans of men and those with schizophrenia, anxiety, bipolar disorder, and ADHD.
Brain aging was also more strongly associated with use of cannabis and alcohol.
"Based on one of the largest brain imaging studies ever done," says lead study author Dr. Daniel G. Amen, a psychiatrist and founder of Amen Clinics in Costa Mesa, CA, "we can now track common disorders and behaviors that prematurely age the brain."
He suggests that improving the treatment of these disorders could "slow or even halt the process of brain aging."
The main reason for the study was to learn more about how aging affects the risk of Alzheimer's disease.
Alzheimer's and brain aging
Increasing age is a "known risk factor" for Alzheimer's disease. Most cases are diagnosed in people aged 65 and older. The risk of developing it "doubles every 5 years" after this, and nearly a third of people over 85 years old have it.
"Understanding the influence of aging on the brain," note the study authors, "remains a challenge in determining its role as a risk factor for Alzheimer's disease."
The brain might only account for about 2 percent of body mass, but it receives up to 20 percent of blood pumped by the heart. This blood travels through some 370 miles of microvessels in the brain.
There is increasing evidence that sporadic Alzheimer's disease — that is, the type that does not run in families and accounts for most cases — is primarily a disease of the blood vessel system.
There is also evidence that nearly all risk factors for Alzheimer's disease involve a component that reduces delivery of blood in the brain, and that problems with microvessels precede changes in brain tissue and cognition.
Yet, the brain's system of blood vessels is an "under-investigated area of brain aging."
The study analyzed 128 brain regions
Dr. Amen and his colleagues analyzed blood circulation patterns in 128 brain regions on the SPECT scans.
They used a statistical tool to identify average age trajectories for the age range of the group and used another statistical tool to identify clusters of brain regions that best predicted chronological age.
They then used that model to determine a "brain estimated age" for each person from their brain scans. Accelerated brain aging was calculated as the difference between chronological age and brain estimated age.
Further analysis revealed links between premature brain aging and certain behaviors and disorders, as shown in the following list:
- schizophrenia — 4 years of premature brain aging
- cannabis use — 2.8 years
- bipolar disorder — 1.6 years
- ADHD — 1.4 years
- alcohol abuse — 0.6 years
There was no association between depression and premature brain aging.
The researchers suggest that their findings will help further study into how psychiatric disorders alter patterns of blood flow in the brain.
"The cannabis abuse finding was especially important, as our culture is starting to see marijuana as an innocuous substance."
Dr. Daniel G. Amen