Researchers suggest that long-term caffeine consumption may worsen the behavioral symptoms of Alzheimer's.
In a study of mice with Alzheimer's, researchers found that prolonged exposure to caffeine was linked to increases in behavioral symptoms of the disease, such as anxiety.
Lead researcher Dr. Lydia Giménez-Llort — from the Universitat Autònoma de Barcelona in Spain — and colleagues recently reported their results in the journal Frontiers in Pharmacology.
The most widely recognized symptom of Alzheimer's is memory loss, but the disease can present a number of other symptoms, including delusions, hallucinations, irritability, anxiety, and depression. Dr. Giménez-Llort and her team refer to these as the behavioral and psychological symptoms of dementia (BPSD).
Studying caffeine's effect on BPSD
For instance, a number of studies using mouse models have concluded that coffee can protect against the development of Alzheimer's. Even in studies that took data from human participants over long periods of time, coffee appears to lower the risk of cognitive decline, Alzheimer's, and other dementias.
How coffee might protect against Alzheimer's is not clear, but one study concluded that a minor component — eicosanoyl-5-hydroxytryptamide — could provide the answer.
Regardless of these findings, however, for individuals who already have Alzheimer's, the effects of caffeine consumption may not be so beneficial, according to Dr. Giménez-Llort and her team.
The researchers came to their conclusion by studying the effects of caffeine on mouse models of Alzheimer's disease.
"The mice develop Alzheimer's disease in a very close manner to the human patients with early-onset form of the disease," explains first author Raquel Baeta-Corral, also of the Universitat Autònoma de Barcelona.
She adds, "They not only exhibit the typical cognitive problems but also a number of BPSD-like symptoms, so it is a valuable model to address whether the benefits of caffeine will be able to compensate its putative negative effects."
To find out, the team added caffeine to the rodents' drinking water from the ages of 6 to 13 months, at a dose of 0.3 milligrams per milliliter.
The researchers explain that previous studies have found that this dosage leads to a daily caffeine intake of around 1.5 milligrams in mice, which is the equivalent to about 500 milligrams in humans, or five cups of coffee per day.
BPSD increased for caffeine-consuming mice
At 13 months of age, the mice took part in a series of experiments that assessed their cognitive and behavioral symptoms of Alzheimer's.
The study revealed that rodents that drank the caffeinated water had greater BPSD — including anxiety and neophobia, or a fear of unfamiliar objects or situations — compared with those that consumed plain water.
Furthermore, they found that caffeine had little benefit for learning and memory in the rodents.
These findings, say Dr. Giménez-Llort and colleagues, suggest that we should be cautious in recommending coffee and other caffeinated products to adults with Alzheimer's disease.
"These results confirm that caffeine, despite its everyday use and relative lack of government regulation, is a potent compound with multifaceted effects," say the authors, adding:
"We speculate that over a chronic treatment with caffeine, the exacerbation of anxiety-like BPSD symptoms may partially interfere with the beneficial cognitive effects to the extent that they can be in the opposite direction."