Adverse Effects Associated with Coffee
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 levels of cholesterol. In 1994, researchers at the Agricultural
University in Wageningen (The Netherlands) identified two chemicals in
coffee that may raise cholesterol levels. The chemicals, cafestol and
kahweol, are members of a chemical family called diterpenes in coffee
oils. The amount of diterpenes varies with the brewing method. Drip-brewed
coffee, instant coffee, and percolated coffee contain only minimal amounts
of diterpenes. Boiled coffees, such as Greek, Turkish, espresso, and those
made in a French "press" coffeemaker, may have 6 to 12 mg diterpenes in a
5-ounce cup. The Dutch researchers estimate that drinking five cups of
press-brewed coffee or 15 espressos a day might raise cholesterol levels 8
to 10 points.
Elevated levels of homocysteine. The American Heart Association has
identified high levels of homocysteine, an amino acid by-product of
protein digestion, as an independent risk factor for heart disease. A 1997
study at the University of Bergen (Norway) found that even moderate coffee
consumption (five or fewer cups a day) is linked to higher blood levels of
homocysteine. This may explain the results of a 1995 study at Boston
University School of Public Health in Brookline, Massachusetts, showing
the risk of heart attack 2.5 times higher among women who drank 10 cups of
coffee a day than among those who averaged less than one cup.
Increased severity of premenstrual syndrome
(PMS). Beta-estradiol and progesterone, two hormones that rise and fall
during the monthly menstrual cycle, directly affect brain levels of
adenosine (see above). Beta-estradiol (an estrogen), which rises just
before ovulation, keeps adenosine from slowing down nerve cell activity,
which may be why many women feel pleasantly energized at mid-cycle.
Progesterone encourages adenosine; it's a soothing hormone. That may be
why many women feel tense and irritable when progesterone levels fall just
before menstrual bleeding begins. Because caffeine alters adenosine
activity in the brain, drinking coffee may make beta-estradiol's "highs"
higher and progesterone's "lows" lower.
Pregnancy-related studies. Caffeine slows
the flow of blood to the placenta, makes the fetal heart beat faster, and
lowers the level of estradiol in a pregnant woman's body. A number of
epidemiological human studies suggest (but have not proven) that consuming
more than 300 mg caffeine a day, about the amount in three cups of coffee,
may slightly increase the risk of spontaneous abortion or giving birth to
a low birth weight infant or one with microcephaly (an abnormally small
head and brain).
NOTE: Caffeine passes into breast milk, so nursing
mothers are usually advised to avoid coffee.
Withdrawal symptoms. Caffeine is a drug for
which you develop a tolerance; the more often you use it, the more likely
you are to require a larger dose to produce the same effects and the more
likely you are to experience withdrawal symptoms (headache, irritation) if
you stop using it. The symptoms of coffee-withdrawal can be relieved
immediately by drinking a cup of coffee.