Caffeine and Health: The Latte Letdown
Millions of people rely on caffeine for a morning boost. But researcher Roland Griffiths says that caffeine likely causes the run-down feelings they are trying to stave off. "A large part of what they are experiencing is the suppression of low-grade withdrawal," said Griffiths, a professor at the Johns Hopkins University School of Medicine.
"They wake up, they feel a little groggy, they take coffee. The effect is 'Oh, wow, this increases alertness, it makes me feel more clearheaded.' What they aren't recognizing is if they didn't consume caffeine, they'd wake up and be able to concentrate," he said.
Withdrawal Is Real
Habitual caffeine use can lead to dependence. 1 When regular consumers quit abruptly they can experience withdrawal -- even if that abstinence is just overnight.
"Caffeine withdrawal is characterized by headache, lethargy and irritability and sometimes nausea, vomiting and difficulty concentrating," Griffiths said. Those effects vary, and some people have no symptoms. But about 13 percent of people experience impairment that interferes with everyday activities, Griffiths said.
Culture Awash in Caffeine
Conscientious consumption begins with understanding how easy it is to unconsciously ingest caffeine.
Most adults get their caffeine from coffee, but the mild stimulant can be found in surprising places. Certain orange sodas have more caffeine than cola, and many sports drinks are caffeine-fueled. Some seemingly soothing teas come with a caffeine jolt. It's well-known that chocolate contains caffeine, but traces can be found in other treats like espresso frozen yogurt.
"Very low doses of caffeine -- like 30 milligrams -- are behaviorally active and mood-altering," Griffiths said.
* Adults in the United States consume an average 280 milligrams of caffeine each day -- about 17 ounces of brewed coffee or 84 ounces of soft drink2.
* Beginning in the 1980s, the U.S. Food and Drug Administration advised pregnant women to avoid caffeine, or consume it sparingly, but the agency has no guidelines on daily intake for other healthy adults or children 3.
* Health Canada determined that for most adults moderate caffeine use -- 400 to 450 mg/day -- is not linked to health problems. But the agency recommends a much lower threshold for children ages 4 to 12 4.
* Many physicians recommend that people with certain medical conditions, like anxiety, insomnia and some kinds of stomach or heart problems, quit or curb their caffeine consumption.
* Caffeine ingested at mealtimes seems to impair the metabolism of carbohydrates in people who have type 2 diabetes, according to a 2004 study suggesting that people with diabetes should reduce caffeine in their diets 5.
* Caffeine can cause acute spikes in blood pressure, but a 2005 study found no association between habitual coffee drinking and increased risk for hypertension 6.
* There has been no consensus from studies searching for a direct link between caffeine or coffee consumption and coronary heart disease, according to the American Heart Association 7.
* A small Costa Rican study found that for light or occasional coffee drinkers, as little as one cup of coffee can trigger heart attack in inactive people and others with heart disease risks 8.
* For people who are not sleep-deprived, caffeine increases vigilance and can improve reaction times. Those positive effects were not found for higher cognitive processes like learning and memory 9.
* It can take between three and five hours for caffeine to metabolize -- to dissipate by half from the blood stream. So caffeine's effects can persist 10 to 12 hours 10,11.
* Caffeine is sometimes used to correct breathing problems in premature infants 12.
* Frequent smaller doses of caffeine later in the day may be more effective in keeping people awake -- versus a venti-sized cup of coffee in the morning. 13.
What We Know About Joe
In recent years, a string of large, multiyear studies have found that heavy and habitual coffee drinkers develop type 2 diabetes less often than moderate coffee drinkers and non drinkers 14. Similar studies have linked regular coffee drinking with lower rates of gallstones, colon cancer and Parkinson's disease 15.
"Many of these things have been epidemiological studies, not experimental research, so they don't demonstrate how caffeine could be a possible mechanism for that effect," said Duke University researcher James Lane.
Lane and other caffeine researcher are skeptical that caffeine - or even coffee - can be credited with these health benefits. "It's always coffee drinking, not caffeine, that spares you from diabetes," Lane said.
"There's a lot of attention paid to the large epidemiological studies. People tend to read too much into them," Lane said. "What they are really saying is there's a correlation between coffee drinking and a reduced risk of diabetes. But they can't say that it's a causative effect." Lane suspects there is something else about the people who drink coffee that is the real factor which prevents them from getting diabetes.
"The thing that's most obvious is that they don't drink soft drinks," Lane said. "If you are drinking, say five cups of coffee a day - you are a regular coffee drinker - it's probably the case that you are not drinking five or six Cokes." Large epidemiological studies have linked heavy soft drink consumption with a spiked risk for type 2 diabetes.
Caffeine researcher Roland Griffiths says he's noticed marketing efforts pushing the health benefits of coffee, but he wants to separate science from spin.
The science on coffee's ability to improve performance and thinking is equally confusing. Very few studies have been done well that allow you to differentiate caffeine withdrawal from caffeine's direct effects, said Griffiths, a professor at Johns Hopkins School of Medicine.
"For regular coffee drinkers, there's no clear evidence, that the caffeine is actually improving mental performance, versus just preventing people from suffering withdrawal," Lane said.
Nonetheless, Lane said, the few cognitive tests on people who do not normally consume caffeine prove that caffeine is stimulating at the least. Caffeine content varies widely with bean type and roasting method, but the 100 milligrams in one 6-ounce cup of coffee can make you more alert, Lane said.
"I remember some older studies, where they found that typing speed might increase, but complex decision-making didn't," he said.
Roland Griffiths, Ph.D.
Johns Hopkins University School of Medicine