Why Tea Has Caffeine

Why tea has caffeine: plants do not waste energy producing chemicals they do not need - that would be an evolutionary blind alley - so there must a good reason why tea has caffeine. In 1984, Dr. James A. Nathanson, a neurologist at Harvard Medical School, published the first evidence in Science. Dr. Nathanson discovered that caffeine, a purine alkaloid, is a potent natural insecticide which, at significant concentrations, kills numerous insects within hours or a few days at most. Caffeine altered behavior, reduced food consumption, and interfered with reproduction in tobacco hornworms, milkweed bugs, meal worms, butterfly larvae and mosquito larvae. Dr. Nathanson said this natural insecticide works by inhibiting an enzyme called phosphodiesterase in insects' nervous systems. Phosphodiesterase breaks down a substance called cyclic AMP which nerve cells use for signaling. Without phosphodiesterase, cyclic AMP builds up in insects' nerve cells to concentrations that interfere with the cells' functions.

Caffeine can accumulate in significant concentrations in insects' bodies because they lack the complex suite of enzymes present in the human liver that readily break it down. A typical insect will have principally the enzymes needed to digest its food and few insects can detoxify caffeine fast enough to survive ingesting very much of it.

Tea plants, Camellia sinensis, are preyed upon by 1,031 different insect pests worldwide, so defense against them is the principal reason why tea has caffeine. Thankfully for tea drinkers, the caffeine produced by the Camellia Sinensis plant interferes with eating in these insect pests and paralyzes them.

The most vulnerable parts of the tea plant are new leaves and buds. It should be no surprise that caffeine is concentrated there. The many teas made from those tender, young leaves and buds naturally tend to have more caffeine than those made from mature leaves lower down on the plants. The mature leaves are more challenging for insects to attack: their stronger structures are harder to bite and chew, so they can survive with less of the insecticide in them.

Research has also shown that injury to a C. sinensis plant, whether from insect attack or a fungus infection, will induce the plant to produce a lot more caffeine at the site of the injury anywhere on the plant. So, defense against disease may be another reason why tea has caffeine.

It is clear that C. sinensis does not have caffeine in order to provide people with a pleasant stimulant in their morning cups of tea. We are just lucky that we get a boost in alertness, energy, and the ability to concentrate and to focus from tea plants' defensive system. We get the benefits of this stimulant and the antioxidants and other beneficial chemicals in tea at very little cost without being one of the reasons why tea has caffeine.

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