Caffeine’s effects will naturally depend on how much you consume, and the type of person you are. Photo / 123rf
Caffeine’s effects will naturally depend on how much you consume, and the type of person you are. Photo / 123rf
For many, a caffeine fix is key to starting the day – an expert explains the biological changes that begin with that morning tea or coffee.
The United Kingdom is a nation fuelled by caffeine. We drink about 100 million cups of tea a day, according to the UK Tea & Infusions Association; and, says the British Coffee Association, somewhere in the region of 95 million cups of coffee. And that’s before we even mention energy drinks.
Yet the health advice surrounding caffeine can sometimes be confusing. A study published in the journal BMJ Evidence-Based Medicine found that pregnant women should cut out caffeine completely to help avoid miscarriage, low birth weight and stillbirth. This is in contradiction to the current guidance in the UK, which states that a daily caffeine intake equivalent to two cups of medium-strength coffee (200mg) is safe for pregnant women.
What is undeniable is that caffeine brings about a biological change in our bodies. We asked Thomas Sanders, a Professor of Nutrition & Dietetics at Kings College London, to explain the process, from the moment a drop of the elixir passes our lips.
For those of us who require a caffeine fix to get out of bed in the morning, reaching for the cafeteria or teapot is second nature. In terms of what happens from then, caffeine’s effects will naturally depend on how much you consume, and the type of person you are. So best to read the timings in this article as a guide rather than an exact timetable.
As a general rule, the average half-life of caffeine in the body is roughly between five and six hours for healthy adults. “The important thing to stress is that there is quite a lot of variation in the individual response to coffee; some of that might be genetic, and there may be also gender differences in the way we break down coffee as well,” says Prof Sanders.
8.05am: The placebo effect
There’s few things more pleasing in life than the first sips of coffee, which seemingly make you feel more awake by the second. However, that immediate alteration in your mood is likely to be a placebo rather than a biological change, especially if you’re in the routine of consuming caffeine every morning.
“To feel the effects of coffee, you’ve got to let it absorb into the bloodstream,” says Prof Sanders. “What you’re feeling at this stage is only likely to be a psychological effect.”
The 20-minute mark comes one of the most enviable – and fleeting – effects of caffeine. Photo / 123rf
8.20am: The energy boost
This is where things get interesting. It takes approximately 20 minutes for caffeine to be absorbed into your bloodstream, so by now you should be starting to feel the positive effects.
“The first thing you experience is an increase in heart rate,” says Prof Sanders. “If you’re in a low state of arousal, it will give you a slight lift, which is why many people come to rely on their cup of coffee in the morning.”
It’s also why people with heart conditions, such as arrhythmia, are advised to avoid drinking a strong morning pick-me-up.
Within these 20 minutes, your mental performance has already improved; you will feel more alert, switched on and able to tackle tasks. The flow of coffee into the bloodstream causes adrenaline to be released, activating our ‘fight or flight’ mode. This can actually sharpen our vision too, which probably explains why the morning spreadsheets feel easier after a flat white or two.
(Prof Sanders says your concentration levels probably continue to improve incrementally from here, topping out at around an hour. It really depends on the quantity of caffeine you’ve had, and your metabolism.)
Also at the 20-minute mark comes one of the most enviable – and fleeting – effects of caffeine: what Prof Sanders called “a rush of euphoria”. It’s why your colleagues are happiest when they have a flat white in their hand.
8.30am: Nature calls
Caffeine is a diuretic, so around half an hour after your morning cup, you may feel the need to urinate (this can happen as quickly as five minutes after you’ve drunk it). However, a study has found that a small cup has no links to dehydration, meaning those who consume coffee in moderate amounts don’t need to overcompensate with extra water.
“People who have bladder or prostate problems might want to be more careful when they have a cup of coffee, as the diuretic effect could be more potent,” says Prof Sanders.
9.30am: The effect on your gut
If coffee is your caffeine of choice, this is the moment when you might feel rumblings in your midriff.
The compounds in coffee stimulate the bowel, resulting in waste being pushed out faster than usual. So, says Prof Sanders, 60-90 minutes after consumption, you may feel a “bit of a cramp in the gut”, indicating it’s time to pay another visit to the office facilities.
This happens with decaf coffee, too – it’s a substance within coffee itself, rather than the caffeine, that causes the rumblings. But don’t assume it’s a negative consequence. “Coffee drinking has been associated with a lower risk of colorectal cancer – and one view is because of its effect on gut motility,” says Prof Sanders.
Coffee has also been shown to lower the risks of type-two diabetes. A Harvard study showed that people who increased their coffee intake over a four year period had 11% lower risk of the disease than those who didn’t increase their coffee consumption.
There is a debate in the medical community about the extent to which coffee can irritate our stomach acids.
“For some people, black coffee can increase gastric secretion of acid; but not always. The evidence is equivocal, although some people do say if you’ve got an acidic stomach, avoid black coffee,” says Prof Sanders.
Headaches, excessive tiredness, an inability to concentrate, and irritability are signs of a caffeine crash. Photo / 123rf
11am: The dreaded crash
You’ve powered through your morning meeting, blitzed through your inbox and even found the time to water your rather sorry-looking desk plant. You feel invincible. That is, until you start to feel an aching tiredness creeping in. This, my friends, is the caffeine slump.
“If you had your first cup of coffee at 8am, it’s likely that the effect on your body will have completely worn off by 11; you need regular hits of it to maintain these effects,” said Prof Sanders.
Signs of a caffeine crash include headaches, excessive tiredness, an inability to concentrate, and irritability. That task that you euphorically promised to complete this morning is suddenly looking much less appealing.
12pm: The craving
The beginning of the end, if you will. For while the caffeine has left your system, it’s still very much on your mind.
“When you’ve been consuming something for a while, the receptors in your brain adapt,” says Prof Sanders. “These take a bit of time to get back to normal after you’ve removed coffee from the system, as there’s an expectation that you’re going to get another hit, and that’s going to wake you up.”
This expectation is what leads many of us to reach for an afternoon cup, starting a vicious cycle well into the afternoon.
Due to the caffeine content, it’s widely agreed amongst experts that consuming coffee late in the day can disrupt sleep. One study, published in the Journal of Clinical Sleep Medicine, found that caffeine consumed six hours before bed still impacted sleep – even if participants no longer felt the effects.
Of course, a poor night’s sleep can only mean one thing; a strong coffee in the morning. And so, the bleary-eyed cycle continues.
