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How much caffeine is too much?

Although individuals seem to differ in their vulnerability to caffeine’s influence, if drunk in moderation, the risks appear negligible.
A passerby walks past a latte at Zeitgeist Kunst and Kafee in Seattle. Research suggests that although individuals differ in their vulnerability to caffeine’s influence, if drunk in moderation, the risks appear negligible.Anthony Bolante / Reuters file

A day without a latte, cup of tea, or caffeinated soft drink is unthinkable for many people. Yet caffeine poses some health risks. Although individuals seem to differ in their vulnerability to caffeine’s influence, if drunk in moderation, the risks appear negligible.

Studies on caffeine discount any risk of cancer. A major report from the American Institute for Cancer Research, based on numerous studies, concluded that coffee has no link to cancer risk.

Drinking more than four cups of coffee a day, however, may increase the risk of heart problems. In fact, a new study suggests that even two six-ounce cups of coffee a day may increase blood test values that measure inflammation.

If future research confirms these findings, there may be cause for concern. But it’s too early to severely limit your coffee consumption for this reason, because two large American studies show no effect of coffee or caffeine on the incidence of heart disease.

Osteoporosis warning
Earlier research seemed to show that caffeine increases the loss of calcium, raising the risk of osteoporosis. Even in a fairly recent study, women aged 65–77 who drank more than 300 milligrams (mg) of caffeine daily — about 18 ounces of regular coffee — showed greater bone loss over a three-year period than those who drank less. But the bone loss occurred only among a minority of women with an unusual variation in their cell vitamin D receptors.

In fact, high caffeine consumption only seems to cause bone loss in elderly women who don’t get enough calcium. As long as elderly women get the recommended 1,200 mg of calcium a day, it should be safe for them to drink up to 300 mg caffeine or about 18 ounces of coffee or its equivalent. Caffeine does not appear to adversely affect the bones of premenopausal women at all.

At one time, some consumer advice claimed that caffeinated drinks deplete the body’s fluid levels because caffeine increases urination. More recent research shows that a person’s fluid balance is not significantly affected by a moderate use of caffeine.

Bad for high blood pressure?
Since some studies suggest that two to three cups of coffee can raise blood pressure around 10 points, many physicians limit people with high blood pressure to 200 mg (two six-ounce cups of coffee) per day or less. However, regular caffeine consumers may develop a caffeine tolerance that prevents blood pressure elevations, according to other studies.

The greatest reason people drink caffeinated beverages is to increase their energy and alertness. Studies show that 100 to 200 mg of caffeine (about 1 to 2 cups of regular coffee) are enough to achieve these results. When caffeine consumption climbs to 250 to 700 mg per day, people may experience nausea, headaches, sleep difficulties or increased anxiety. People may have heart palpitations with more than 1,000 mg.

Some day, there may be individual advice for everyone about how much caffeine they can safely consume. Research, however, is only beginning to explain why caffeine’s influence varies so much. For instance, genetic differences in the enzymes that metabolize caffeine cause some people to process caffeine quickly, thus reducing their exposure to caffeine’s effects sooner. There are also inherited differences in cell receptors.

For now, you should stick to moderate amounts of caffeine. For an adult, that means no more than 300 mg daily, which is three 6-ounce cups of coffee, four cups of regular tea, or six 12-ounce colas.

A person may want to have even less, depending upon how caffeine affects their sleep, blood pressure, digestive system and overall well being. Children, nursing mothers or pregnant women, on the other hand, should have much less because caffeine will have stronger effects in smaller bodies.