Neurobiologist and author, 'The Other Brain'
Posted: 09/04/2013 2:28 pm
There is no doubt that alcohol abuse causes brain damage and several other health problems, including cancer and liver disease. Some of the brain injury associated with alcohol abuse can be seen on a brain scan (MRI) as physical changes in brain structure and loss of brain tissue in wide-spread regions throughout the brain.
One of the most prominent changes associated with alcohol consumption involves the massive bundles of nerve fibers that interconnect neurons in different regions of the brain into functional circuits. These fibers are coated with a white-colored electrical insulation, called myelin, which is essential for transmission of electrical signals. These tracts of white matter streaking through the brain are the brain's information highways, and damage to them will impair any cognitive function that depends on information transmission through the communication cables. Loss of memory, slowed thinking, impaired problem solving and decision making are especially vulnerable to damage caused by alcohol consumption, because it disrupts white matter connections to the cerebral cortex and deep brain structures necessary for these mental functions.
Remarkably, a large body of new research has revealed that aerobic exercise not only builds muscle, it builds brain tissue. Aerobic exercise stimulates the birth of new neurons in specific parts of the brain where neurons can still divide in adults, including the hippocampus, which is involved in learning. Exercise protects against cognitive decline in aging and neurological diseases, including Alzheimer's, and it strengthens the integrity of white matter tracts to the extent that the beneficial changes can be seen on an MRI.
These recent discoveries motivated researchers Hollis Karoly and colleagues at the University of Colorado to ask whether aerobic exercise could prevent the damaging effects of heavy alcohol consumption on white matter in the human brain. Identifying any new treatment that could reverse brain damage caused by alcohol consumption would have profound health benefits for tens of thousands of individuals who consume alcohol. According to this new study, there is an effective treatment that requires no medication and has no negative side effects -- aerobic exercise.
To answer this intriguing hypothesis, the researchers compared the level of alcohol consumption in a population of men and women between the ages of 21-55 with the integrity of their white matter. This was accomplished by using an MRI brain imaging method that is highly sensitive to white matter integrity, called diffusion tensor imaging (DTI). Three conclusions were supported by the data, two of them confirming what was already shown in the literature, and the new finding reported here.
(1) White matter tracts in the brain are strongly affected by alcohol consumption. This was seen throughout the brain, but it was especially pronounced in some fiber tracts known to be necessary for higher level thinking and memory and other functions impaired in those who abuse alcohol. For example, the external capsule (EC) and superior longitudinal fasciculus (SLF) were especially sensitive to damage caused by drinking alcohol. When white matter integrity is graphed against the total number of alcoholic drinks consumed in 60 days (or other measures of alcohol consumption), white matter integrity drops in direct proportion to the amount of alcohol consumed.
(2) Conversely, white matter integrity increased in people who reported doing aerobic exercise in the last three months, and greater improvements were seen in those who did more than the average amount of exercise.
Both of these effects confirm and extend the result of other studies. The third result was that in people who exercised, the loss of white matter integrity caused by alcohol consumption was prevented or reduced, depending on how much exercise was done and which particular white matter tract in the brain is examined.
For example, in people who reported doing a moderate amount of aerobic exercise in the last three months (that is, the average amount of aerobic exercise among all participants), the integrity of the EC white matter tract was maintained even for the heaviest drinkers. Even better results in preserving white matter integrity were seen in subjects reporting an above average level of aerobic exercise. The steep, straight-line drop in white matter integrity plotted against the amount of alcohol consumption, leveled out completely in those participating in high levels of aerobic exercise; that is, no deleterious effects of alcohol consumption at any level of consumption could be seen in the white matter tracts of these people. Again, the magnitude of the effects differed somewhat in different white matter tracts, but in general the beneficial effects of exercise were evident throughout many white matter tracts in the brain.
The study also sorted the data according to self-reporting of cannabis use and tobacco smoking, because both of these have been implicated in white matter damage. Even accounting for these other effects on white matter structure, the beneficial effects of aerobic exercise on white matter integrity were still seen. The researchers conclude that the most damaging effects of alcohol consumption on white matter integrity are seen in those people who do not exercise regularly, "alcohol consumption did not appear to be associated with white matter damage among individuals who exercised regularly."
The design of this experiment can only provide correlative data. The associations revealed here must be tested in further experiments to show that there is a causal link between exercise and protection against white matter damage caused by drinking alcohol, and to uncover the biological mechanisms for the protection. However, these findings revealing the protective effects of aerobic exercise on preventing white matter brain damage in drinkers are compelling and valuable, regardless of whatever biological link to explain this correlation may be found in the future.
All of the facts stated in this article are documented by citations to the scientific literature in the following paper reporting these new results:
Karoly, H.C., et al., (2013, in press) Aerobic exercise moderates the effect of heavy alcohol consumption on white matter damage. Alcoholism: Clinical and Experimental Research. Published on-line in advance of print.
For additional information on white matter see:
Fields, R.D. (2008) White Matter Matters, Scientific American, 298: 42-9.
Fields, R.D. (2008) White matter in learning, cognition and psychiatric disorders. Trends Neurosci. 31: 361-70.