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Tea and Caffeine - The Big Picture
First, the basics.
The earliest record of caffeine consumption dates back to at least 2700 B.C., when Chinese Emperor Shen Nung drank hot brewed tea.
Caffeine is a naturally occurring, flavorless chemical that acts as a stimulant to the central nervous system, and as a diuretic. Caffeine can also be synthetically produced.
It appears naturally in coffee, tea and cocoa beans, and is added in small amounts to colas to enhance their flavor. It is also added to appetite suppressants, cold medicines and pain relievers.
Chemically, caffeine is a member of the xanthine family. Caffeine is odorless, has a bitter taste and is highly soluble in hot water. Caffeine occurs naturally in coffee, tea, cocoa, kola nuts and a variety of other plants.
In moderation, caffeine has beneficial effects on the body: it increases alertness, stimulates metabolism and contributes to an increase in dopamine levels in the blood, which improves mood.
Tea and Caffeine
Just as with coffee and many commercial beverages such as cola drinks, the relief from fatigue provided by many teas is one big reason for their popularity. This is due to caffeine, and caffeine has been a matter of controversy. It is a stimulant that has been shown to speed reaction time, increase alertness, and improve concentration. The physical effects include stimulation of digestive juice, the kidneys, and the metabolism in ways that possibly help eliminate toxins. An increasing of mental alertness, shortening of reaction time, and improving efficiency of muscle action is brought about by caffeine's stimulation of the heart and respiratory system, bringing more oxygen to the brain.
Choosing the Right Tea by Time of Day
Not all teas are created equal, in terms of caffeine content. In general, black tea has the most caffeine (40 milligrams per serving - half that of coffee at 80 milligrams per serving), followed by Oolong tea (30 milligrams per serving), green tea (20 mg/serving), white tea (15 mg/serving), decaf tea (2mg/serving), and herbal tea (0mg/serving).
It should come as no surprise, then that many people enjoy tea in part for the relief from fatigue it provides, and make their tea choices in no small part by how much caffeine a particular tea contains. So, many people enjoy black teas in the early morning, oolong teas for lunch, green teas in the afternoon, and white or herbal teas in the evening.
Caffeine and Health
The role of caffeine in the development of certain diseases and conditions has been the subject of extensive research in recent years.
A number of studies investigating the impact of caffeine in the development of cancer have consistently failed to establish a relationship. In fact, tea is one of the richest sources of flavonoids, a powerful group of antioxidants. The role of antioxidants in the prevention of free radical damage has led to suggestions that tea maybe anti-carcinogenic. For more information on this subject please refer to the fact sheet ‘Tea and Cancer.’
A number of studies have investigated the relationship between caffeine and heart disease. A review of the available data on caffeine and health concluded that 400mg caffeine/ day does not adversely affect cardiovascular health. Furthermore it has been suggested that the beneficial effects of the flavonoids present in tea may offset any potential adverse effects of caffeine. The Committee on Medical Aspects of Food Policy concluded that ‘there is little evidence that caffeine itself has any relation with CHD risk’ in the 1994 Nutritional Aspects of Cardiovascular Disease report.
Observational studies have suggested that caffeine may play a role in protecting against Parkinson’s disease, , although further research is required to confirm this.
In a study of 301 regular headache sufferers, researchers found that a combination of ibuprofen and caffeine was better than either drug alone in relieving pain. Although a caffeine ‘pill’ was used in this trial, the researchers believed that caffeinated beverages would work just as well. However, they did warn that chronic headache sufferers should avoid caffeine because it might exacerbate symptoms. More work is required in this field before firm conclusions about caffeine and pain relief can be drawn.
Caffeine crosses the placenta and achieves blood and tissue concentrations in the foetus that are similar to maternal concentrations. For this reason advice published by the Food Standards Agency recommends that pregnant women should limit their intake of caffeine consumption to less than 300mg/ day (equivalent to 6 cups of tea/ day). At this level there is little evidence to suggest that the health of the unborn child or mother is affected.
Bone and Calcium Balance
The data to suggest that caffeine potentially adversely influences bone metabolism includes epidemiological studies investigating the relationship between caffeine and the risk of osteoporosis (as characterized by low bone mineral density) and increased susceptibility to fractures, as well as metabolic studies examining the effect of caffeine on calcium homeostasis.
The results of these studies are inconsistent. This is because interpretation of caffeine’s effect on bone metabolism is complicated by other risk factors such as calcium intake, age, cigarette smoking and alcohol intake that need to be accounted for.
Reviewing the evidence to date Nawrot et al suggest that the significance of caffeine’s potential to adversely affect calcium balance and bone metabolism is dependent on lifetime caffeine and calcium intakes and is biologically more relevant in women. He concludes by saying that the current data indicates that caffeine intakes of <400mg/ day do not have significant effects on bone status or calcium balance in individuals ingesting at least 800mg of calcium a day.
There has been much concern in the United States recently about the possible dangers of caffeine. As regards tea, it should be noted that all types of tea contain less caffeine than coffee. The caffeine content of some of our teas is available here.
Caffeine tolerance varies greatly among individuals, and an excess of it is toxic. Some research has shown a possibility that caffeine can interfere with fetal development, including lowering birth weight and contributing to skeletal and other abnormalities. Until they reach the age of seven or eight months, babies cannot get rid of caffeine metabolites, and traces of caffeine can appear in breast milk too. Due to these concerns, pregnant and nursing mothers should limit or avoid any beverage with caffeine, including tea.
Caffeine content is also affected by the length of the infusion in water. Black tea infused for 5 minutes yields 40-100 milligrams, whereas a 3-minute infusion produces 20-40 milligrams, or half as much. Twenty cups of green tea yield 240 milligrams, or about 12 milligrams per cup.
Because tea bags contain broken leaves of smaller size, they produce an infusion with more caffeine than loose tea does. This is also true of very fine loose tea.
Despite recent publicity about caffeine, the fact remains that the consumption of caffeine at intakes of 300mg/ day has no adverse effects in the vast majority of the adult population. For this reason an average intake of four cups of tea a day is well within the level considered safe.