Some of you may have read headlines like these: “For a restful night, stay off the coffee after 5pm” (The Daily Telegraph 16.11.2013); or “Drinking even one strong coffee in the afternoon can knock an hour off your sleep”, a couple of weeks ago. The reports were advising us to avoid all caffeinated beverages for at least 6 hours prior to sleep. In light of these headlines should you drink coffee in the evening?
The newspaper reports are based on a small study carried out by researchers from Henry Ford Hospital, Wayne State College of Medicine in Detroit and Zeo Inc. Researchers tested the effects of a 400mg caffeine pill taken either at bedtime, 3 hours or 6 hours before sleep. They found that the caffeine dose appeared to disrupt sleep even when taken 6 hours before bedtime; reporting that participants slept an average of 41 minutes less.
However, before you ditch that late night tea or coffee, I would like to point out some facts about the study, which question the validity of its findings. Firstly, the study didn’t contain a fair representation of the general population. There were only 16 participants and people who drank more than five caffeinated beverages a day were excluded. In fact, as the average daily consumption of caffeine for participants was only 115mg, it would suggest that they were all only light users.
Secondly, the participants were giving a large amount of caffeine; 400mg to be precise. The researchers appear to justify this dosage by claiming that a commercially prepared 16oz (480ml) cup of brewed coffee can contain up to 500mg of caffeine. Other research contradicts this claim:
Image credit: http://www.thrillist.com
The graphic above shows the caffeine content per a fluid ounce of various American coffee retailers. As you can see, (if you ignore ‘Deathwish Coffee’ which I believe must be spiked with extra caffeine) you would need to drink over 19oz (570ml) of Starbucks coffee or nearly 44oz (1.3ltrs) of McDonald’s coffee to consume 400mg.
Source: “Espresso Coffee – The Science of Quality” edited by Illy & Viani. Beverage size: Espresso 25-35ml; Moka pot 40-50ml; all other beverages 150-190ml
The actual caffeine content in coffee varies considerably due to a number of factors, such as: the location where the coffee is grown, how long the coffee is roasted and how the coffee is brewed. Even if you brewed two coffees at home, using the same brew method, the caffeine content in each brew is likely to differ. However, to consume 400mg of caffeine is almost certainly going to involve drinking multiple cups of coffee. The researchers even admitted to this in their study, estimating that an 8oz (240ml) cup of home brewed coffee contained 100mg of caffeine.
Thirdly, seeing as caffeine is widely reported to be a stimulant, it’s hardly surprising that giving the participants nearly 4 times their normal daily amount of caffeine disrupted their sleep. If their bodies are only used to metabolising 115mg of caffeine its surely no surprise that giving them an additional 400mg to process is going to have a negative effect on their sleep. It would have been more interesting to have run the study longer than the 4 nights, to see how quickly the participants’ tolerance to caffeine increased. Would their sleep be less affected after a few weeks or maybe a month?
So I think the only thing you can really take away from the study is that if you only normally consume 1-2 cups of coffee or tea a day, and you want a good night’s sleep, its advisable not to drink the equivalent of 4 cups of coffee in the evening.