A couple of cups of coffee may help our brains process some words faster, a small experiment suggests. But we only get the message faster if the words are emotionally positive. The study included 66 healthy young men. They were told to consume no caffeine, nicotine or alcohol in the 12 hours before the experiment. The men were randomly divided into 2 groups. One group took a tablet containing 200 milligrams of coffee, about the amount in 2 to 3 cups of coffee. Each person in the other group received a placebo (fake) pill. Half an hour later, the men were given tests that involved being shown a series of real and invented words. They had to press buttons to indicate whether a word was real or not. Men who took the caffeine pills did this faster and more accurately for words with a positive emotional connotation. They did not perform better than men who got the placebo pills for recognizing neutral or negative words. The journal PLoS One published the study online. HealthDay News wrote about it November 8.

By Howard LeWine, M.D.
Harvard Medical School

What Is the Doctor's Reaction?

You often hear people say things like "Don't talk to me. I haven't had my coffee yet." Researchers from Germany offer us new insight into why we might feel that way. The study comes from the Department of Psychology at Ruhr University.

In general, people recognize and process the meaning of words faster if the words have a positive emotional slant. What these researchers found is that caffeine speeds up that link even more. But caffeine did not speed up how quickly people recognize and process emotionally neutral or negative words.

Low doses of caffeine tend to put you in a more positive mood. Caffeine also generally helps you do mental tasks faster and with fewer errors. Now we can add the faster processing of positively charged emotional content. These are good explanations for why you want that first cup of coffee before talking to anyone.

How caffeine affects the brain is not completely understood. But here is how most experts explain it.

Caffeine gets absorbed in the stomach and small intestine. It enters the blood stream and is distributed throughout the body, including the brain.

Once it reaches the brain, caffeine probably has multiple targets. But the main one seems to be adenosine receptors. Adenosine is a chemical that dampens brain activity. This counters the action of another brain chemical, dopamine.

Dopamine acts as a brain stimulant and mood enhancer. By hogging the adenosine receptor sites, caffeine doesn't allow adenosine to dampen brain activity. This puts the balance in favor of dopamine. It leads to feeling more awake and alert, with a more positive mood.

What Changes Can I Make Now?

Overall, coffee is generally safe when used in moderation. But the key word is moderation.

In some people, too much caffeinated coffee can raise blood pressure. Teenagers seem to be more susceptible to an increase in blood pressure from caffeine.

Coffee also can interfere with how well your body absorbs iron and calcium. But you need to drink a lot of coffee for it to greatly lower the amount of iron and calcium in your bloodstream. And it's not the caffeine that interferes with the absorption. It's related to another ingredient in coffee called phenolic acid. So decaf coffee also will decrease absorption of these minerals.

Depending on how you make your coffee, it can raise cholesterol levels a little. Again, it's not the caffeine that influences cholesterol levels. It's the coffee oil from the bean. If you boil or press your coffee, then the coffee oil gets into the brew. However, today most coffee in the United States is filtered through paper. And filtered coffee does not increase cholesterol levels.

So what's the bottom line? If you are already a coffee drinker, enjoy it. If you don't drink coffee, processing of words that convey positive emotions is not a good enough reason to start.

There's probably some amount of coffee (and other drinks containing caffeine) that carries a risk of real health hazards. I am still unclear as to what that level is for an otherwise healthy adult.

My advice: If even one cup of coffee makes you jittery or anxious, or interferes with sleep, that is one cup too many. I am honest with patients. I don't know if 10 cups of coffee per day is too much. I would not drink that much; 3 cups per day is my own limit.

What Can I Expect Looking to the Future?

The great majority of medical studies looking at coffee drinkers have shown better health outcomes for people who drink coffee. Almost none have suggested that coffee is bad for you. In fact, my personal limit of three cups per day may be too cautious. Maybe I'd be better off drinking more!