On Food and Cooking

Caffeine is the most widely consumed
behavior-modifying chemical in the world. It
is an alkaloid (p. 238) that interferes with a
particular signaling system used by many
different cells, and therefore has several
different effects on the human body. Above
all, caffeine stimulates the central nervous
system, relieves drowsiness and fatigue, and
quickens reaction times. It also increases
energy production in muscles and so their
capacity for work. It’s said to improve mood
and mental performance, though recent
studies suggest that these may be the result of
relieving the initial symptoms of overnight
caffeine withdrawal! Less desirably, in high
doses it causes restlessness, nervousness, and
insomnia. It has complex effects on the heart
and arteries, and can produce an abnormally
fast heartbeat. There is some evidence that
caffeine speeds the loss of calcium from bone,
so habitual consumption may contribute to
osteoporosis.