What Coffee Does To Your Body, And How Much Is Too Much?

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We Brits drink an astonishing amount of coffee a day - around 70 million cups! But as a nation that can't live without a brew, it's essential to know the effects of caffeine and how much is considered too much.

Unless you guzzle more than four cups a day, you're not likely to be facing any risk. A new report from scientists looking at more than 740 studies published between 2001 and 2015 confirmed that it's safe to consume up to 400mg of caffeine, equivalent to four cups of filter coffee or 300mg for pregnant women.

If you prefer a cup of breakfast tea to coffee, one cup of black tea contains between 30-80mg of caffeine. Drink no more than five cups a day.

What happens after drinking one cup?

Although we can drink up to four cups per day and remain healthy, it can take as little as five minutes for the effects of caffeine to be felt in the body. Shortly after taking your first sip, your blood pressure increases slightly, and as caffeine molecules enter the bloodstream they bind to adenosine receptors in the brain (responsible for promoting sleep) and stimulate the release of adrenaline. After 20 minutes, you have an increased feeling of alertness.

Drinking a coffee with or after a meal can facilitate digestion as caffeine raises acid levels in the stomach. If consumed on an empty stomach, however, the acid can cause irritation and bloating.

What happens if I drink more than one cup?

Just one cup can increase your heart rate to 100bpm (a healthy resting rate is between 60 and 80 beats per minute), which can take up to an hour to return to normal. Drinking additional coffee may cause further heart rate acceleration.

The effects of caffeine are said to enhance memory for a day after consumption, and studies have also shown regular coffee drinkers have a reduced risk of developing Alzheimer's and dementia, among many other health benefits.

What happens if I drink over the recommended limit?

The study also looked at the effects of too much caffeine over time, which includes damage to cardiovascular and reproductive systems, bone health deterioration, gut problems, increased likelihood of depression and anxiety, headaches, dizziness and vomiting.

More immediate effects of too much caffeine include an energy crash soon after consumption and insomnia, as caffeine delays the rise in melatonin levels essential for a good night's sleep.

When is the best time to drink coffee?

About an hour after you wake up, after the body's initially high cortisol levels subside. But don't leave it too late - caffeine has a half-life of four to six hours, which means that it takes 100mg of caffeine between four and six hours to reduce to 50mg in the blood.

Isa Jaward
Isa Jaward

Isa Jaward is a journalist from London who has written for the likes of Time Out, The Guardian and Music Week.