25-09 - Flipbook - Page 37
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Why caffeine and what happens if you have too much?
Caffeine is a stimulant that can make you feel more alert and less sleepy due
to its effect on the brain and nervous system.
Lewis James, from the School of Sport, Exercise and Health Sciences at
Loughborough University, says there is good evidence that caffeine can help
make exercise feel easier.
It's become one of the most regularly used supplements among athletes.
As you exercise your body produces a chemical called adenosine which
makes you feel tired. Caffeine blocks the adenosine receptors in your nerves,
so your brain perceives less pain and fatigue.
But it acts on other parts of the body too - including the cardiovascular
system - which can be risky.
High levels can cause a rapid heart rate, abnormal heart rhythms and
seizures.
Although rare, there are documented deaths from excess caffeine.
Some people are more sensitive to caffeine than others and can feel
nauseous, anxious and irritable, and get headaches even at lower doses.
Generally, up to 400mg of caffeine a day appears to be safe for most
healthy adults - that's around four cups of instant coffee.
Tea contains a bit less, so five cups a day is usually fine.
Pregnant women are advised to halve daily intake to 200mg or less.
Children and teenagers are also more susceptible to the risks and potential
for an overdose.
This is why energy drinks containing over 150mg of caffeine, for example, are
already required by EU law to carry labels stating: "High caffeine content. Not
recommended for children or pregnant or breast-feeding women".
Watch for other drinks or food that contain caffeine
Dr van Dam says it can be easy to overload. Caffeine is found in many drinks
and some foods, so it is important to check how much you are consuming.
"While it's harder to overdose on coffee, with these products it's easier,
especially if young people are using energy drinks too."
He says some products, when you check them in the laboratory, contain
more caffeine than they claim on the labelling.
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Coffee: a mug contains about 100-140mg of caffeine, but it can vary
widely
