What is it about coffee? HARVARD HEALTH NEWSLETTER 01/2012
Research is showing benefits for everything from depression to liver disease. Is it just the caffeine? Remember when people (and their doctors) used to worry that coffee would harm their hearts, give them ulcers, and make them overly nervous? In excess, coffee, and more particularly, caffeine, can cause problems. But the fretting about two or three cups a day, or even more, is fading as study results suggestive of health benefits from coffee keep on coming in. Just in the past year, researchers have reported findings that coffee drinking is associated with a lower risk of depression among women, a lower risk of lethal prostate cancer among men, and a lower risk of stroke among men and women. Go back a little further, and you'll come across re-ports of possible (it's not a done deal) protective effects against everything from Parkinson's disease to diabetes to some types of cancer (see sidebar on the next page). Caffeine has been studied more than any other ingredient in coffee, and it tends to get credit if the body part benefited is the brain. But coffee contains literally a thousand different substances, and some of the lesser lights are thought to be responsible for healthful effects in other parts of the body. Some studies show caffeinated and decaffeinated coffee as having the same effect, which suggests that something else in coffee is involved. It gets complicated, though. Caffeine and some of these other substances in coffee seem to have their good and bad sides, and coffee's overall effect may depend on how much they cancel each other out. Caffeine: Good for the brain, bad for other parts? Caffeine is the most commonly consumed psychoactive drug in the world, and some of its behavioral effects (such as arousal) may resemble those produced by cocaine, amphetamines, and other stimulants.
Coffee consumption accounts for about 75% of the adult intake of caffeine in the United States, although that might be changing among younger adults with the growing popularity of energy drinks. The caffeine content of coffee varies greatly, depending on the beans, how they're roasted and other factors, but the average for an 8-ounce cup is about 100 milligrams (mg). Tea has Caffeine content 200 150 50 35* 8-oz cup 8.4-oz 8-oz "short" cup of Lipton can of Starbucks green tea Red Bull "bold" coffee '35 mg presumes a single tea bag steeped in 8-ounce cup ''Per 8.4-ounce can about half as much caffeine as coffee. Decaffeinated coffee has some caffeine, but the 2 to 4 mg in an 8-ounce cup is a smidgen compared with the caffeina ted version. The lethal dose of caffeine is about 10 grams, which is equivalent to the amount of caffeine in 100 cups of coffee.
Caffeine gets absorbed in the stomach and small intestine and then distributed throughout the body, including the brain. The amount circulating in the blood peaks 30 to 45 minutes after it's ingested and only small amounts are around eight to 10 hours later. In between, the amount circulating declines as caffeine gets metabolized in the liver. Tobacco and marijuana accelerate caffeine metabolism, which reduces the time caffeine circulates in the body. Oral contraceptives slow it down, so they have the opposite effect. Researchers have identified genes that influence a person's natural risk of caffeine person's natural risk of caffeine metabolism, which might explain why some people are exquisitely sensitive to caffeine while others are not. Caffeine probably has multiple targets in the brain, but the main one seems to be adenosine receptors. Adenosine is a brain chemical that dampens brain activity. By hogging adenosine's receptors, caffeine sets off a chain of events that affects the activity of dopamine, another important brain chemical, and the areas of the brain involved in arousal, pleasure, and thinking. A part of the brain affected by Parkinson's disease, called the striatum, has many adenosine receptors; by docking on them, caffeine seems to have some protective effects. Outside the brain, caffeine can be a performance enhancer, boosting the strength of muscle contraction and offsetting some of the physiological and psychological effects of physical exertion. But, especially in the short term, it also has negative effects, which include raising blood pressure, making arteries stiffer, and increasing levels of homocysteine, insulin, and possibly cholesterol. Habitual use may cause some of these effects to wear off. For some conditions, though, coffee may have some benefit despite, rather than because of, caffeine.
Cafestol and kahweol:
Filtering Coffee drinkers concerned about cholesterol weren't happy about some early study results showing that coffee seems to increase cholesterol levels, and "bad" LDL cholesterol levels in particular. But upon closer inspection, the bad news turned out to be not so bad, because the cholesterol-raising effect seems to be limited to coffee that hasn't been filtered, which includes Turkish coffee, coffee brewed in a French press, and the boiled coffee consumed in Scandinavia.