from the fact that its molecular structure is similar to that of adenosine, a natural chemical
by-product of normal cell activity. Adenosine is a regular chemical that keeps nerve cell activ-
ity within safe limits. When caffeine molecules hook up to sites in the brain when adenosine
molecules normally dock, nerve cells continue to fire indiscriminately, producing the jangly
feeling sometimes associated with drinking coffee, tea, and other caffeine products.
As a rule, it takes five to six hours to metabolize and excrete caffeine from the body.
During that time, its effects may vary widely from person to person. Some find its stimu-
lation pleasant, even relaxing; others experience restlessness, nervousness, hyperactivity,
insomnia, flushing, and upset stomach after as little as one cup a day. It is possible to develop
a tolerance for caffeine, so people who drink coffee every day are likely to find it less imme-
diately stimulating than those who drink it only once in a while.
Changes in blood vessels. Caffeine’s effects on blood vessels depend on site: It dilates coronary
and gastrointestinal vessels but constricts blood vessels in your head and may relieve headache,
such as migraine, which symptoms include swollen cranial blood vessels. It may also increase
pain-free exercise time in patients with angina. However, because it speeds up heartbeat, doc-
tors often advise patients with heart disease to avoid caffeinated beverages entirely.
As a diuretic. Caffeine is a mild diuretic sometimes included in over-the-counter remedies
for premenstrual tension or menstrual discomfort.
Adverse Effects Associated with This Food
Stimulation of acid secretion in the stomach. Both regular and decaffeinated coffees increase the
secretion of stomach acid, which suggests that the culprit is the oil in coffee, not its caffeine.
Elevated blood levels of cholesterol and homocysteine. In the mid-1990s, several studies in the
Netherlands and Norway suggested that drinking even moderate amounts of coffee (five
cups a day or less) might raise blood levels of cholesterol and homocysteine (by-product of
protein metabolism considered an independent risk factor for heart disease), thus increas-
ing the risk of cardiovascular disease. Follow-up studies, however, showed the risk limited
to drinking unfiltered coffees such as coffee made in a coffee press, or boiled coffees such
as Greek, Turkish, or espresso coffee. The unfiltered coffees contain problematic amounts
of cafestol and kahweol, two members of a chemical family called diterpenes, which are
believed to affect cholesterol and homocysteine levels. Diterpenes are removed by filtering
coffee, as in a drip-brew pot.
Possible increased risk of miscarriage. Two studies released in 2008 arrived at different
conclusions regarding a link between coffee consumption and an increased risk of miscar-
riage. The first, at Kaiser Permanente (California), found a higher risk of miscarriage among
women consuming even two eight-ounce cups of coffee a day. The second, at Mt. Sinai
School of Medicine (New York), found no such link. However, although the authors of the
Kaiser Permanente study described it as a “prospective study” (a study in which the research-
ers report results that occur after the study begins), in fact nearly two-thirds of the women
who suffered a miscarriage miscarried before the study began, thus confusing the results.
Coffee