Caffeine appears to have an enhancing effect on memory consolidation, a new study suggests.

For the study, published online January 12 in the journal Nature Neuroscience, 160 healthy volunteers were shown 200 pictures of different everyday items and asked questions about them. They were then given a pill containing 200 mg caffeine or a placebo.

The next day, the participants were given a surprise memory test. They were shown another set of pictures, some the same as before, some new items, and some similar but slightly different.

Those individuals who had taken the caffeine were better able to discriminate the new items and were more likely to detect that the similar items were different from those viewed the day before, senior author Michael A. Yassa, PhD, Johns Hopkins University, Baltimore, Maryland, and University of California, Irvine, told Medscape Medical News.

"My message from this study is that if, like me, you have a coffee habit, and drink several cups a day, this is another reason not to stop it," he commented." But it may not be enough to persuade someone who doesn't drink coffee to start, especially if they are highly reactive to its stimulant effects."

Asked whether these findings have any implications for Alzheimer's disease, Dr. Yassa said, "Our study cannot speak to that but other data from our institution in elderly people has suggested that a moderate caffeine intake is associated with better longevity and a reduction in Alzheimer's disease. This could potentially be a similar mechanism."

Dr. Yassa is planning further brain imaging studies on the effect of caffeine in patients with mild cognitive impairment.

Moderate Dose Best

Participants in the study were not regular coffee drinkers. It was stipulated that they should consume less than 500 mg of caffeine each week (about 2 to 3 cups of coffee). But most actually consumed significantly less than this, only around 70 mg, Dr. Yassa noted.

In an additional study, the researchers looked at whether there was a dose response. They found no effect with 100 mg and equal effect with 200 mg and 300 mg. But the 300-mg dose was associated with more adverse effects, such as headache and nausea.

The results indicate "an inverted U-shaped dose-response curve suggesting that moderate amounts of caffeine (200 mg) may be the most effective at enhancing memory with no significant benefit at higher doses," the authors report.

Caffeine levels in saliva were quantified at 4 time points: at baseline, at 1 hour after caffeine/placebo intake (when levels peaked in the caffeine group), at 3 hours (when they had dropped again), and at 24 hours later (to make sure participants hadn't consumed any more caffeine).

Other studies in humans looking at coffee and memory have shown inconclusive results, but previous studies have generally given caffeine before the test so it is difficult to separate effects on memory and effects on alertness, Dr. Yassa said. "In our study, because caffeine was given after the initial viewing of the items, the effect is more likely to be due to memory rather than alertness," he added.
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