Lower risk of dental cavities. By observation, there appears to be a link between tea drink-
ing and a lower risk of dental decay. In addition, one study of more than 6,000 14-year old
children in the United Kingdom found that those who drank tea had significantly fewer
dental caries than non–tea drinkers, regardless of whether they drank their tea plain or with
sugar or milk and sugar. This result may be attributable to the natural presence of fluorides
in tea leaves.
Methylxanthine (theophylline and caffeine) effects. All methylxanthines are central-nervous-
system stimulants, vasoactive compounds that dilate the skeletal blood vessels and constrict
blood vessels in the brain. Theophylline, which effectively relaxes the smooth muscles in the
bronchi—the small passages that carry air into the lungs—is used as an asthma medication,
but the relatively low concentrations of theophylline in brewed tea are too small to produce
therapeutic effects.
Adverse Effects Associated with This Food
Stimulation of the central nervous system. Taken in excessive amounts, caffeine and theophylline
may cause rapid heartbeat, restlessness, sleeplessness, and/or depression in sensitive individu-
als. Since different people can tolerate different amounts of caffeine and theophylline without
suffering ill effects, exactly which dose produces problems varies from person to person.
Constipation. The tannins in tea may be constipating.
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 tea may make beta-estradiol’s “highs” higher and progesterone’s “lows”
lower. Because tea contains less caffeine than coffee, its effects would be much weaker.
Food/Drug Interactions
Drugs that make it harder to metabolize caffeine. Some medical drugs slow the body’s metabo-
lism of caffeine, thus increasing its stimulating effect. The list of such drugs includes cimetidine
(Tagamet), disulfiram (Antabuse), estrogens, fluoroquinolone antibiotics (e.g., ciprofloxacin,
enoxacin, norfloxacin), fluconazole (Diflucan), fluvoxamine (Luvox), mexiletine (Mexitil),
riluzole (Rilutek), terbinafine (Lamisil), and verapamil (Calan). If you are taking one of these
medicines, check with your doctor regarding your consumption of caffeinated beverages.
Drugs whose adverse effects increase due to consumption of large amounts of caffeine. This list
includes such drugs as clozapine (Clozaril), ephedrine, epinephrine, metaproterenal (Alupent),
Tea