How a cup of coffee affects your body from the first sip

Britons guzzle 70 million cups of coffee each day but few of us realise the extent to which our morning brew affects our bodies from the first sip. Recent research has revealed that a late night shot slows down our internal body clock and stops us sleeping – but it does a whole lot more than have us counting sheep into the early hours.

Coffee is a chemical juggernaut, quickly absorbed and distributed throughout the body, affecting everything from brainpower and eyesight to digestion and bowel function. However you take yours – cold brew, espresso, pour-over or plunged – coffee affects your entire system.

“A single cup of coffee has rapid absorption with caffeine uptake to the blood in just over 20 minutes and will stay in the blood stream for over 12 hours,” says Dr Owen Bain, founder of the Gourmet Focus consultancy.

Pulse and blood pressure

Shortly after drinking coffee, your blood pressure rises a fraction – the effect is more pronounced if you don’t drink coffee regularly. If you stick to one cup, your heart rate actually slows down due to the increase in blood pressure. “However, more than a few cups of coffee can cause heart rate acceleration,” Dr Bain says. For healthy people this is not a problem, but may be an issue for those with underlying problems such as heart disease, high blood pressure or abnormal heart rate, according to some experts.

The gut

Ordering an espresso after a meal makes a certain physiological sense – caffeine raises acid levels in your stomach, which facilitate digestion.  But experts advise avoiding coffee on an empty stomach as the gastric juices can irritate the gut lining, causing pain, bloating and heartburn.

Bowel and bladder

Compounds in coffee stimulate the bowel and can result in waste being pushed out faster than normal – within 5 minutes of drinking it for some people! Because the same thing occurs with decaffeinated coffee, researchers believe that a compound other than caffeine is responsible. But Dr Bain says it’s a myth that coffee makes you urinate more frequently than drinking the equivalent amount of water. “The diuretic effect of coffee is very small, and it is just as hydrating as water,” he adds.

Eyes

Within 20 minutes of drinking coffee, the caffeine causes adrenaline to be released, activating your ‘fight or flight mode’. As a result, your pupils dilate slightly and you might actually have sharper vision.

Brainpower and memory

“Caffeine is a stimulant and 20 minutes after drinking a coffee you can start to feel more alert, with increased concentration, and are less likely to make mistakes,” Dr Bain says. “A recent study showed that coffee could enhance your memory 24 hours after consumption. This may not appear to be long, but most memories are lost within a few hours after learning.” Many studies also suggest that regular coffee consumption over a lifetime is associated with a reduced risk of developing Alzheimer’s disease.

Energy

Don’t rush to grab that first cup when you wake up in the morning, as your cortisol levels are high then and will keep you going for a while. “The best time to drink a cup is about an hour after your get up,” Dr Bain says. The caffeine also increases your heat production, which may help with weight reduction, he says. But after about three hours, the effects of the caffeine start to fade and you may experience a coffee ‘crash’. “This is because the caffeine in coffee doesn’t actually make you more energetic, it just makes you less able to feel that you’re tired,” he says. “So unless you are well rested you will start to feel tired again.”

Lungs

The caffeine in coffee is similar to the drug theophylline, given to patients with respiratory problems, and helps open up the lungs making it easier to breathe.

Mood

Coffee stimulates the release of the feel-good hormone dopamine. “An hour after drinking coffee there is a reduction in anxiety levels and increased feelings of contentment,” Dr Bain says. “Women who are regular coffee consumers have been shown to have less depression.” But he says too much coffee can have the opposite effect, causing anxiety and restlessness.

Sleep

Coffee consumed late in the evening resets the internal body clock by delaying a rise in the level of melatonin, the body’s chief sleep hormone. Fluctuating levels of melatonin help determine the natural time to go to sleep and wake up, so a double espresso three hours before bed time could leave you staring at the clock and unable to sleep.