What You Need To Know About Caffeine In The Diet

Each day, millions of people use caffeine containing drinks, such as tea and coffee, to wake them up in the morning and keep them going throughout the day. Caffeine is not only contained in drinks it is present in foods such as chocolate, and medicines such as pain killers. It has both positive and negative effects on the body.

What is caffeine?

Caffeine is a naturally occurring stimulant found in plants such as coffee and cocoa beans, tea leaves and berries.

How does caffeine work?

Caffeine enters the body quickly through the membranes lining of the mouth, throat, and stomach. It begins to have an effect in the body after 10 minutes and takes about 45 minutes for most of the caffeine in a food or drink to be absorbed through these membranes. The average energy drink or coffee’s effect lasts between 4 and 6 hours.

Caffeine’s main effect is on the brain. It works by blocking the effect of a neurotransmitter called adenosine. Adenosine levels build up during the day and relax the brain to make you feel tired and ready to sleep. Caffeine works by blocking the effect of adenosine and this makes you feel less tired. Caffeine doesn’t replace the person’s need for sleep, but just covers up drowsiness symptoms that adenosine can no longer produce.

What are the negative effects of caffeine?

Short-term adverse effects of caffeine on adults and children can include issues related to the central nervous system such as interrupted sleep, anxiety and behavioural changes. In the longer term, excessive caffeine consumption (above 400mg per day) has been linked to cardiovascular problems and, in pregnant women, stunted foetus development and spontaneous abortion.

Guidelines on caffeine intake

Based on current scientific opinions[1] people sensitive to caffeine, should only consume caffeine in moderation. Pregnant and breast-feeding women are advised not to have more than 200mg of caffeine over the course of a day, which is roughly two mugs of instant coffee or one mug of filter coffee.

Intakes up to 400mg per day consumed throughout the day do not raise safety concerns for healthy adults in the general population, except pregnant and breast feeding women.

For children and adolescents small intakes of caffeine (up to 90mg per day) do not raise safety concerns. As with adults, caffeinated drinks taken close to bedtime may increase the time it takes for children and adolescents to fall asleep and reduce sleep duration.

Which foods and drinks contain caffeine?



Caffeine content (mg)


Cup of filter coffee



Can standard energy drink






Cup of tea



Bar of dark chocolate



Bar of milk chocolate


Source: EFSA

Energy drinks

Since 2004, energy drinks have been the fastest growing sector of the drinks market in the UK. The popularity of consuming energy drinks mixed with alcoholic beverages has also increased. Most energy drinks contain levels of caffeine approximately equivalent to those found in a cup of coffee (approximately 80mg caffeine per 250ml can).

Currently beverages containing more than 150 mg/l caffeine (other than those based on coffee or tea) must carry the statement ‘High caffeine content’.

Are there any benefits to consuming caffeine?

When it comes to exercise, caffeine may increase the use of fat as fuel which can help the glucose stored in muscles last longer, potentially delaying the time it takes your muscles to reach exhaustion. It has also been shown to improve muscle contractions and increase tolerance to fatigue. Studies have shown caffeine can give a mental boost and keep you alert when concentrating on an important task.


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