Abstract
About 85% of the adult population in the Netherlands regularly drinks alcohol. Chronic excessive alcohol intake in alcohol-dependent individuals is known to have damaging effects on brain structure and function. Relatives of alcohol-dependent individuals display differences in brain function that are similar to those found in alcoholics, even if they
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have never been drinking alcohol. This suggests that brain damage in alcohol-dependent individuals is at least partly related to genetic factors. As the majority of people who drink alcohol is not alcohol-dependent, it is important to know the pure effects of alcohol intake on the brains of these individuals. There are indications that moderate alcohol intake also has negative consequences for brain structure and function. However, as these studies did not control for a family history of alcohol dependence, it is unclear what the pure effect of alcohol intake in non-alcohol-dependent drinkers is without the influence of genetic factors related to alcohol dependence.
To investigate the pure effects of alcohol intake on brain structure and function in non-alcohol-dependent drinkers, 96 healthy males and females consuming between 0.5 and 53 drinks per week were recruited via newspaper advertisements. Only individuals without alcohol-dependent relatives up to the second degree were included, so that the possible influence of genetic factors related to alcohol dependence were minimised. Brain structure was measured with magnetic resonance imaging, and brain function was assessed with electroencephalography. Both males and females consuming more than 21 alcoholic drinks per week had lower functional brain connectivity measured on the left side of the brain than males and females consuming 21 drinks per week or less. Additionally, male drinkers with an alcohol intake of more than 6 drinks per week had lower left- and right-sided functional brain connectivity than males consuming 6 drinks per week or less. Furthermore, males with heavier alcohol intake had a greater white-matter volume in the frontal areas of the brain. This global increase in frontal white matter was complemented by a focal decrease in grey matter. In the female drinkers, no relationship between alcohol intake and brain structure was found.
These results suggest that chronic alcohol intake of more than 21 drinks per week impairs brain function in both males and females who are not alcohol-dependent. In males, heavier alcohol intake additionally leads to more white matter and less grey matter in the brain. This finding may reflect that males with heavier alcohol intake have more repair processes in response to focal neuronal damage in the brain. Although alcohol intake was similar across males and females, male drinkers displayed differences in brain function at lower levels of alcohol intake. In addition, alcohol-related differences in brain structure were only found in the males. These gender differences may be explained by behavioural factors (e.g. differences in drinking patterns or beverage choice) or biological factors (e.g. a protective effect of estrogen). Furthermore, as individuals with alcohol dependence or with alcohol-dependent relatives were excluded, the present results may selectively relate to the effects of alcohol intake on brain structure and function.
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