At Medical News Today, we often report on studies yielding the health benefits of drinking coffee. New research, however, now suggests that our beloved cup of joe might have a darker side, after finding that long-term caffeine intake could exacerbate symptoms of Alzheimer's disease.

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.

Around 5.7 million adults in the United States live with Alzheimer's disease, and every 65 seconds, one more person in the country develops the condition.

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

Previous research has suggested that coffee has the potential to lower the risk of Alzheimer's and other dementias. For individuals who already have Alzheimer's, however, 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 mg/mL.

The researchers explain that previous studies have found that this dosage leads to a daily caffeine intake of around 1.5 mg in mice, which is the equivalent to about 500 mg 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."

—Honor Whiteman