according to the results of a large study.
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“With coffee intake, moderation is the key, and especially high levels of consumption may have adverse long-term effects on the brain,” said study investigator Elina Hypponen, PhD, professor of nutritional and genetic epidemiology and director of the Australian Center for Precision Health at the University of South Australia.
“These new data are concerning, and there is a need to conduct further carefully controlled studies to clarify the effects of coffee on the brain.”
The study was published online June 24 in Nutritional Neuroscience.
Potent stimulant
Coffee is a potent nervous system stimulant and is among the most popular nonalcoholic beverages. Some previous research suggests it benefits the brain, but the investigators noted that other research shows a negative or U-shaped relationship.
To investigate, the researchers examined data from the U.K. Biobank, a long-term prospective epidemiologic study of more than 500,000 participants aged 37-73 years who were recruited in 22 assessment centers in the United Kingdom between March 2006 and October 2010.
During the baseline assessment, information was gathered using touchscreen questionnaires, verbal interviews, and physical examinations that involved collection of blood, urine, and saliva samples. An imaging substudy was incorporated in 2014, the goal of which was to conduct brain, heart, and body MRI imaging for 100,000 participants.
The investigators conducted analyses on disease outcomes for 398,646 participants for whom information on habitual coffee consumption was available. Brain volume analyses were conducted in 17,702 participants for whom valid brain imaging data were available.
Participants reported coffee intake in cups per day. Researchers grouped coffee consumption into seven categories: nondrinkers, decaffeinated coffee drinkers, and caffeinated coffee drinkers who consumed less than 1 cup/d, 1-2 cups/d, 3-4 cups/d, 5-6 cups/d, and more than 6 cups/d.
The reference category was those who consumed 1-2 cups/d, rather than those who abstained from coffee, because persons who abstain are more likely to be at suboptimal health.
“Comparing the health of coffee drinkers to the health of those choosing to abstain from coffee will typically lead to an impression of a health benefit, even if there would not be one,” said Dr. Hypponen.
The researchers obtained total and regional brain volumes from the MRI imaging substudy starting 4-6 years after baseline assessment. They accessed information on incident dementia and stroke using primary care data, hospital admission electronic health records, national death registers, and self-reported medical conditions.
Covariates included socioeconomic, health, and other factors, such as smoking, alcohol and tea consumption, physical activity, stressful life events, and body mass index.
The investigators found that there was a linear inverse association between coffee consumption and total brain volume (fully adjusted beta per cup, –1.42; 95% confidence interval, –1.89 to –0.94), with consistent patterns for gray matter, white matter, and hippocampal volumes.
There was no evidence to support an association with white matter hyperintensity (WMH) volume (beta –0.01; 95% CI, –0.07 to 0.05).