The psychological effects of your morning coffee

Many of us use coffee to help us to get going in a morning, or to add a little zing to a flagging workday. But recent research reveals psychological effects that go far beyond boosting alertness, and not all of them are good…

The 'up' sides

Caffeine in coffee is a central nervous system stimulant. It increases alertness and improves focus and problem-solving. And if you're someone who 'uses' caffeinated drinks, such as coffee, to help you to feel more alert for an exam, there is some evidence that it will help. A study specifically on university students found that caffeine led to a "striking improvement" on memory tests taken in the early morning, which is typically a 'low' point for young adults. A separate group of participants who were asked to do some exercise did not show this benefit — so it seems to be down to a direct effect on memory, rather than via a boost to general arousal, the team reports.

Research published last year also expanded the already substantial list of benefits reported for visual processing. The team found that caffeine improved people's ability to detect moving targets — which could mean reacting more quickly to anything from a pedestrian stepping onto the road to a football hurtling your way during a game of five-a-side.

The 'down' side

Beware of drinking coffee before going shopping because this can encourage impulse-buying, according to research published earlier this year. The team found that people who drank just one espresso before going into a shop spent a staggering 50% more money inside than others who'd had a decaf coffee or a drink of water. They were also more likely specifically to go for 'high hedonic' items, such as buttery foods or relaxing products, rather than useful things. Why? The caffeine-drinkers reported feeling more excited (due, no doubt, to a misperception of a caffeine-induced faster heart rate as 'excitement'), and when we are excited, we tend to be more impulsive.

The neither-up-nor-down side

While caffeine improves a range of cognitive abilities, creativity is not one of them. Darya Zabelina at the University of Arkansas and colleagues gave participants either a 200mg caffeine pill (equivalent to one strong cup of coffee) or a placebo, then a battery of tests.

As expected, those with caffeine in their system did better on a problem-solving task, which involved coming up with a fourth word that could link three given words (such as 'cheese' for cottage, swiss and cake). The team also assessed participants' creativity, using a divergent thinking test. The participants had to use simple symbols as the start of a more complex drawing, and come up with as many uses as possible for an everyday object, for example. On these tests, was no difference between the two groups. The researchers speculate that this is because creative thinking is easier when the brain is in a less focused, more relaxed state (which caffeine does not foster).

The social side

If you want someone to feel warmly towards you, hand them a hot cup of coffee. That, at least, is the controversial conclusion of well-publicised research by US psychologists Lawrence Williams and John Bargh. Bargh has run a series of studies that suggest that physical heat or cold affect our perceptions of social warmth. His argument is that from our earliest days, we associate physical warmth with the comforting presence of a caregiver, and that this unconscious association persists into our adult lives. It's been suggested that when we experience physical warmth as an adult, this encourages not only warm feelings towards whoever we are with, but also generates a kind of partial social satiety.

The original 2008 Williams and Bargh study notoriously failed to replicate, and other findings in this field have been mixed. However, some researchers argue that at least some of these inconsistencies could be down to variations in the ambient temperature on the day, or in the room. When ambient temperature was controlled for in a recent study, the team found support for the idea that temperature warmth may indeed influence our social judgements, reducing a desire for social contact.

The limits

Many of us 'treat' a bad night's sleep with an extra cup or two of coffee the next morning. Past studies have led researchers to suggest that all of the cognitive deficits associated with sleep deprivation (including a slower reaction time and poorer concentration) stem from impaired attention. And as caffeine boosts attention, then coffee should indeed at least help with all the problems caused by a lack of sleep. However, a study published last year reported that there is one category of sleep-deprivation deficits that it does nothing to address: 'place-keeping' deficits. These are problems with keeping track of where you are in a relatively complex task, whether that's working through steps in a hospital setting or a factory, or writing an essay. Place-keeping deficits don't stem from impaired attention. So this work suggests that a lack of sleep has broader cognitive impacts — and also implies that it's wrong to assume that coffee will treat all the resulting problems.