I was reading an old article from Bord Bia that said that tea consumption was on the rise at night-time. The reason given was that “people are at home more often and tea is a comforting affordable reliable beverage”.
There have been several papers written on the effect of caffeine on sleep disruption and even more papers written on effect of caffeine on other health issues (good and bad). A major problem in this type of research is that all the papers tend to use very different values for the caffeine content in beverages and foods.
There are plenty of reasons for the variations. Preparation plays a large role and differences in the time and temperature of steeping, the size of the tea leaf and the type of tea used will all influence the caffeine content of tea. The variety of plant, care of the plants, soil nutrients, picking season and the part of plant used will also play a role.
Caffeine is a white, odourless crystal that occurs naturally in coffee, tea and chocolate and is added to colas and energy drinks. After a lot of reading, here is a summary of caffeine content in tea from sources that seems reliable:
Tea (~200ml after one steeping of three minutes)
Chinese white tea – 75mg
Darjeeling white – 56mg
Indian Green – 59mg
Kenyan Green – 58 mg
Chinese Oolong (Ti Kwan Yin) – 37mg
Assam (FTGFOP) – 86mg
Darjeeling Black (SFTGFOP1) – 54mg
For comparison here are some for coffee and other beverages:
Coffee (ground roasted) – 115mg
Coffee (instant) – 80mg
Cola – 20mg
Decaffeinated coffee – 4mg
Espresso, single shot – 75mg
Espresso, double shot – 150mg
Red Bull (250ml can) – 80mg
It seems to be generally accepted that there are 6mg of caffeine per 30g serving. But it seems to vary a lot:
70% Green and Black dark Chocolate (30g) – 4.5mg
Green and Black milk chocolate (30g) – 2mg
White chocolate (30g) – 0mg
Cadbury dairy milk (28g) – 15mg
Herbal tea – 0mg
(Note: other substances like theobromine, tanninic acid, caffeol also play a role)
I found it surprising how high the caffeine content of green tea is. Many claim that green and white tea have less caffeine than oolong or black tea because of the minimal oxidation. It seems to be well-proven now that this is not the case. White tea in particular uses the bud of the plant which has been shown to have a higher caffeine content that the leaf. I guess most people wouldn’t have a can of coke before bed but I wonder if they know that a Chinese white tea has three times as much caffeine?
With a few exceptions, herbal tea or tisanes have no caffeine at all. That includes Rooibos so there is a huge selection of tea alternatives for night-time. I’ve been going through a rough time with sleep lately so now I only drink tea up to about 3pm and right before bed I drink hops tea. It seems to really help. And no, by hops tea I don’t mean beer though sometimes that helps too :-).
Barone JJ, Roberts, H.R. (1996), Caffeine consumption, Food and Chemical Toxicology, Volume 34, Issue 1, January 1996, Pages 119–129.
Richardson, B. (2009), De-bunking the At-Home Decaffeination Myth Story, Fresh Cup January 2009
Chin JM, Merves ML, Goldberger BA, Sampson-Cone A, Cone EJ. (2008), Caffeine content of brewed teas. J Anal Toxicol. 2008 Oct;32(8):702-4.