The Facts about caffeine
We all know how we feel when we haven’t had our morning fix! Caffeine is the most widely used psychoactive substance in the world with coffee being the most popular caffeinated product. Every day in the UK around 55 million cups of coffee are consumed, and we rank 5th in the world for our high tea consumption.
In addition to tea, coffee, chocolate, cola drinks and energy drinks there are other less obvious caffeine containing products. Some over-the-counter and prescription medications including cold and ‘flu remedies, pain-relief treatments, and diet pills also contain this stimulant. Also mate tea, and guarana, a Brazilian plant that is often sold in herbal energy drinks are other lesser-known sources of caffeine.
Hidden sources of caffeine
Caffeine is also used as flavouring in some consumer products. The Food Standards Agency (FSA) only requires specific labelling for high caffeine drinks and foods where caffeine has been added for a ‘physiological effect’. Therefore when caffeine is used as flavouring, the amount added is generally not labelled.
Another less known fact is that decaffeinated coffee is not the same as ‘caffeine free , as studies have shown they can contain up to 20mg of caffeine per cup (a normal cup of coffee contains about 80mg caffeine).
Recommended daily allowance
The general advice is that 4-5 cups of coffee (400mg/day) is safe (half that in pregnant women). The amount of caffeine per cup depends of various factors, method of brewing, how dark and grind of bean, size of cup, how many spoonfuls of coffee were used.
It takes about 20minutes after consuming a caffeinated drink for the effects to be realised, and peak levels in the blood stream within 1-2 hours. The half-life of caffeine – that is the time for your body to eliminate half the initial dose, is between 3-7 hours in a healthy person. We become less efficient at metabolising caffeine as we get older and generally speaking females show more of a physiological response to caffeine. Also there is a known genetic influence, making some individuals more sensitive to the stimulant effects of caffeine, increasing the likelihood of experiencing insomnia and anxiety. (study 69).
Effects of Caffeine.. Positive and negative
Caffeine can have positive as well as negative health effects. Its main social use is to promote wakefulness, but is also acts as appetite suppressant, performance enhancer, and is used as treatment for sleep apnoea in premature babies.
The undesirable effects of caffeine include prolonging the time it takes to sleep, reducing sleep quality and quantity as well as heightening physical symptoms of anxiety.
How caffeine affects sleep.
The chemical adenosine is involved in sleep regulation, by attaching to specific adenosine receptors in the brain, which results in drowsiness. Caffeine works as an adenosine antagonist, blocking the receptors and promoting wakefulness.
Several studies have shown that heavy caffeine consumers (>4 cups coffee/day) more commonly experienced difficulties getting off to sleep, frequent awakenings through the night, shorter sleep duration and their sleep quality was affected. In one study when caffeine intake was considerably high (>8 cups/day) sleep duration was curtailed by 40minutes on average.
Almost 30% American adolescents consume caffeinated drinks (mainly soda, but also coffee) on a daily basis. Those consuming high caffeine intake (>1 drink/day), were almost twice as likely to report difficulty sleeping, and problems with daytime sleepiness.
Caffeine is metabolised in the liver by the same enzyme that breaks down the hormone melatonin (the natural sleep promoting hormone). One scientific study in which an average of 5 cups of coffee were consumed in the afternoon and evening, over a week, showed a 30% reduction in the melatonin secretion over the peak time 1-4am.
The amount of caffeine in 1-2 expressos, consumed within 16 hours of bedtime has been shown to make superficial sleep longer at the expense of deep sleep.
The evidence clearly shows caffeine’s disruptive effect on sleep, compromising deep sleep and impacting on sleep quality. However it is hard to know whether daytime sleepiness leads to increased caffeine consumption, or whether sleep disruption due to caffeine is the cause of increased sleepiness. An interesting finding from a study looking at chronic caffeine consumption in rats, showed raised levels of adenosine (the sleep regulator chemical) in their circulation. This is definitely an area for further research.
Take home message
Think about your daily caffeine intake, when you consume it, and be aware of where caffeine may be hiding! Be mindful of giving enough time for your last caffeinated cup to have a chance to be eliminated from your body if you don’t want it to impact on your sleep. I generally recommend 4pm as a good cut off for caffeine for those who go to bed at night time. Those working night shifts will undoubtedly be using caffeine to help promote wakefulness, while the rest of us hopefully slumber!