Drinking Alcohol Daily May Speed Loss of Nerve Cells in Patients’ Brains

While people who smoke cigarettes are more likely to be diagnosed with multiple sclerosis, MS patients who are daily alcohol drinkers are more likely to show signs of faster neurodegeneration, a new study highlights.

The findings suggest that quitting smoking and cutting back on alcohol would be beneficial for people with MS, though the scientists stressed a need for further research.

The study, “Associations of Alcohol Consumption and Smoking With Disease Risk and Neurodegeneration in Individuals With Multiple Sclerosis in the United Kingdom,” was published in JAMA Network Open.

Smoking tobacco is a well-established risk factor for MS. But the effects of alcohol on disease risks are less clear, with studies reporting both an increased and a decreased risk of MS with alcohol intake.

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Ways in which smoking and drinking affect how MS progresses also remain incompletely understood. To learn more, a team led by scientists in the U.K. analyzed data from the UK Biobank, a large biomedical database.

Their analysis included data covering 71,981 people between the ages of 40 and 69. Of them, 20,065 had no documented health problems. The others all had at least one recorded health condition, including 179 people with an MS diagnosis.

Researchers first looked at whether smoking, alcohol intake, and other factors were associated with a significantly altered risk of developing MS.

When the healthy individuals were used as a control group, results showed that current smokers were at a roughly three times higher risk of MS compared with people with never smoked. The risk of MS was about 60% higher for former smokers.

Current smoking also was tied to an increased MS risk when individuals with disorders other than MS, defined as comorbidities in the study, were used as the reference group.

Drinking moderate amounts of alcohol (once a month to up to four times a week) was tied to a significantly lower likelihood of MS compared with never drinking or drinking only on special occasions — but only when healthy individuals were used as controls. When people with other disorders were used in the comparison, those lower odds lost significance, meaning they might be due to chance.

The researchers noted that the “sick quitter effect” — the tendency for people with health problems to cut back on alcohol intake — may have influenced this study’s findings of a lower MS risk, noting a need for further research.

Similarly, obesity was tied to increased chances of developing MS when comparisons were made between the MS group and healthy individuals. No difference was seen when people with other disorders were the control group.

“Only smoking remained significantly associated with odds of having an MS diagnosis when using the control group with comorbidities,” the scientists wrote. “This finding illustrates the importance of choice of control group, because risk factors and protective factors are likely similar across various diseases, which can obscure associations.”

Researchers then did looked at correlations between these factors and the thickness of the macular ganglion cell layer and inner plexiform layer (mGCIPL), a region in the eye’s retina whose thinning is associated with neurodegeneration and atrophy (shrinkage) in the brain.

Among MS patients, results showed a significant negative correlation between alcohol intake and mGCIPL thickness. In other words, people with MS who drank more alcohol — with a high intake defined as daily drinking — tended to have a thinner mGCIPL, indicating greater neurodegeneration. That association remained significant after taking into account factors like sex, living in deprived areas, intraocular pressure, and smoking status.

“Participants with self-reported high alcohol intake had almost 5% thinner mGCIPLs, a substantial difference in retinal thickness,” the researchers wrote. “We observed a linear negative association of alcohol with mGCIPL thickness in MS, without protective effects of moderate alcohol consumption.”

This is in line with previous studies that linked “alcohol use with lower brain volumes and a large recent population-based study, which found that alcohol consumption explained 7.7% of variance in gray matter volume, compared with 1.7% by smoking status,” they added.

People who smoked or were obese or overweight also tended to have a thinner mGCIPL, but the difference did not reach statistical significance.

“Our findings suggest that neurodegenerative processes occurring in MS may interact with neurotoxic effects of alcohol and smoking, resulting in greater neuronal cell death,” the researchers wrote.

They also suggest “that current recommendations for the general population regarding smoking and moderating alcohol consumption may be particularly relevant for individuals who have been diagnosed with MS or who are at risk for the disease,” the team added.

The scientists stressed a need for further research to validate these findings. They noted several limitations in the present analysis, particularly a lack of quantitative information on smoking and drinking behaviors in the Biobank database.