So do cappuccino lovers need to worry about limiting their consumption?
One expert, Matthew Johnson, associate professor in the department of psychiatry at Johns Hopkins University, explains how caffeine works in the body and when to cut back.
Caffeine works by blocking adenosine, a neuromodulator in the brain that puts the brakes on excitatory neurotransmitters like dopamine and norepinephrine. “Caffeine allows these stimulating chemicals to flow, which can have a rousing effect, even at very low doses,” says Dr. Johnson, a psychopharmacologist who studies the influence of drugs on behavior and mood.
Some people will get edgy from a weak cup of tea. For others, a double espresso is required to get them into the shower in the morning.
Most coffee drinkers are familiar with at least some symptoms of overindulging—nervousness, excitement, insomnia, rambling thoughts. But a large majority of people who consume caffeine don’t experience severe consequences, Dr. Johnson says.
There are some case reports of students experiencing major anxiety after drinking a dozen cups of coffee, Dr. Johnson says. But overdosing would be difficult, “unless folks took multiple caffeine pills or drank many cans of energy drinks” such as Red Bull.
It is possible for a person to die from too much caffeine, “but that would mean about 14,000 milligrams, or around 140 8-ounce cups of coffee in one day,” Dr. Johnson says. Consuming that much would be difficult because of coffee’s self-limiting nature. “One cup makes you feel good and alert, but five cups may make you feel like your stomach is cramping,” he says. “You feel wired and you wouldn’t typically be able to go overboard.”
While clinicians may observe benefits and risks of caffeine intake, the effects are still being debated in academic circles, Dr. Johnson says. “The evidence that unfiltered coffee increases LDL cholesterol levels is convincing,” he says, referring to the “bad” type of cholesterol. “But it’s the mortality studies that count the most,” he says.
One study suggests mortality benefits at up to six cups of coffee a day, Dr. Johnson says. Another suggested mortality risks in people under 55 who drink more than four cups a day. As a result, “I would be hesitant to say that we’ve reached any final answer,” he says.
Current research into depression has looked closely at glutamate, one of the neurotransmitters affected by caffeine, Dr. Johnson says. “In a recent study, those who drank two to four cups of caffeinated coffee had fewer depressive symptoms, and the opposite was true for those who lowered their intake,” he says. That doesn’t mean depressed patients would benefit from a steady diet of triple lattes. “If a patient is depressed and predisposed to panic attacks, for example, caffeine might make the condition worse,” he says.
The most convincing evidence indicates you’re probably not at risk for major side effects if you consume up to about four 8-ounce cups of filtered coffee, or around 400mg, early in the day, Dr. Johnson says. “If you’re drinking under four cups a day and not having any side effects, then you’re probably OK,” he says.