Caffeine

Scientific studies (review articles) on the relationship between tea/coffee/caffeine and disease prevention:
One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of randomized, placebo-controlled double blind clinical trials (RCTs) will answer the following question:
"Do taking dietary supplements make sense?" Yes for a positive conclusion and no for a negative conclusion.

One swallow does not make a summer. A famous Dutch saying that could not be any more obvious. Just because one single scientific study about a certain topic makes certain claims, it does not necessarily mean it is true. On the other hand, a review article (a collection of scientific studies on a certain topic) of cohort studies or case-control studies will answer the following question:
"Should I change my diet?".

1. 540 mg/d green tea catechins supplementation reduces UV-induced damage due to erythema inflammation
2. Coffee and tea consumption reduce glioma
3. <11 g/day alcohol and <2.8 cups/day coffee reduce cognitive deficits
4. Tea consumption may reduce colorectal cancer in female
5. Green tea reduces stomach cancer
6. Tea reduces brain cancer in American population
7. Decaffeinated coffee consumption could reduce ovarian cancer
8. 3 cups/d coffee consumption reduce risk of all-cause mortality
9. Higher alcohol intake increases stroke 
10. Daily 1 cup tea decreases all-cause mortality among elderly
11. Dairy products, high purine vegetables, soy foods and coffee decrease gout
12. High consumption of soft drinks increases ulcerative colitis
13. 1 cup/d green tea reduces esophageal cancer among women
14. High tea consumption reduces hip fracture risk among women
15. Habitual tea consumption reduces nasopharyngeal cancer
16. Tea consumption increases bone mineral density
17. Daily 3 cups of tea decrease risk of depression
18. Green tea decreases LDL cholesterol level in overweight or obese people
19. At least 7 cups/day green tea intake reduce prostate cancer
20. Green tea reduces blood pressure in subjects with hypertension
21. Green tea may causally improve risk factors of cardiovascular disease
22. Green tea causally lowers blood pressure in healthy individuals
23. Green tea consumption decreases blood pressure among overweight and obese adults
24. Postoperative coffee or caffeine consumption causally reduces postoperative ileus
25. 1-6 cups/day caffeinated or decaffeinated coffee is associated with reduced type 2 diabetes risk
26. <400 mg coffee bean extract supplementation reduces blood pressure in hypertensive patients
27. Coffee consumption is associated with a lower level of serum CRP in humans
28. Coffee consumption is associated with a higher circulating level of adiponectin in women
29. <3 cups/d coffee is essential for the prevention of dyslipidemia 

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• Tea is the most widely consumed beverage after water.
• The tea plant, Camellia sinensis, is a member of the Theaceae family.
• There are three main types of tea, all originating from the same species (Camellia sinensis), produced by different degrees of fermentation of tea leaves:
  1. black tea, where fermentation is high;
  2. green tea, where fermentation is very low and;
  3. oolong tea, where fermentation is intermediate.
• Polyphenols dominate the chemistry of nonvolatile compounds in green tea and they represent 36% of dry weight of the green tea leaves.
• Tea polyphenols, known as catechins, usually account for 30% to 42% of the dry weight of the solids in brewed green tea.
• The four major tea catechins (flavan-3-ols) are:
  1. (−)-epigallocatechin-3-gallate (EGCG);
  2. (−)-epigallocatechin (EGC);
  3. (−)-epicatechin-3-gallate (ECG) and;
  4. (−)-epicatechin (EC).
     EGCG represents the most abundant one of tea catechins (50% to 80% of total catechins).
• Tea catechins have antiviral, anticarcinogenic, and antioxidant activity. Tea catechins act as potent antioxidants via direct scavenging of reactive oxygen and nitrogen species (ROS and RNS), induction of defence enzymes and binding and chelating of divalent metals, such as copper and iron.
• Tannins are a class of compounds in tea, especially black tea, which tend to have a bitter flavor and astringent properties. Teas high in tannins can be described as tannic.
• The average cup of green tea contains from 10-50 mg of caffeine.
• No one knows exactly how or when coffee was discovered, though there are many legends about its origin.
• The history of coffee goes at least as far back as the 10th century, with a number of reports and legends surrounding its first use.
• The average coffee tree produces 10 pounds of coffee cherry per year, or 2 pounds of green beans.
• The word "coffee" entered the English language in 1582 via the Dutch koffie,  borrowed from the Turkish kahve, in turn borrowed from the Arabic qahwah.
• Caffeine (1,3,7-trimethylxanthine) is a stable alkaloid and one of several related methylxanthines. It is found in various plants such as coffee and cocoa beans, tea leaves, guarana berries and the kola nut.
• Caffeine is chemically related to the adenine and guanine bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA).
• Caffeine is a central nervous system (CNS) stimulant of the methylxanthine class. It is the world's most widely consumed psychoactive drug.
• Caffeine is 99% absorbed from beverages and reaches peak concentrations in the serum in 30 to 60 minutes. The average half-lives time ranging from 4 to 6 hours.
• Moderately heavy coffee drinkers have mean plasma caffeine concentrations of 4.4 mg/L over 24 hours.
• The effect of caffeine varies for each individual depending on how much is consumed, the schedule of consumption and the elimination half-life.
• The typical caffeine content of brewed coffee is 85 to 100 mg per 175-mL (6-oz) cup and of instant coffee is 65 mg per cup.
• In humans, caffeine is metabolized into more than 25 metabolites, the primary ones being paraxanthine, theobromine and theophylline.
• Daily dose at which withdrawal occurs is approximately 2.5 cups of coffee. Symptoms of coffee withdrawal include headache, drowsiness, fatigue, decreased performance, dysphoric mood change, muscle pain/stiffness, flulike symptoms, nausea/vomiting, anxiety and caffeine craving.
• According to EFSA (European Food Safety Authority) daily caffeine intakes from all sources up to 400 mg per day do not raise safety concerns for adults in the general population, except pregnant women. Daily caffeine intakes from all sources up to 200 mg per day by pregnant women do not raise safety concerns for the fetus.