How much do you really know about what caffeine is doing to your body?

Many of us punctuate our days with cups of coffee. We rely on the energy buzz in the morning so that we are ready for the day, before sipping down another couple for midday and afternoon pick-me-ups.

But now that it is part and parcel of our daily routines, we don't often stop to think about the impact that it might be having on our health or if we should be cutting back.

So, here is everything you need to know about your favourite hot beverage.

How many cups of coffee should you drink a day?
Experts tend to agree that most people can safely consume up to 300mg of caffeine a day - and, as one cup of instant coffee contains around 100mg of caffeine - you should not exceed three cups a day.

The NHS suggests that pregnant women should consume no more than 200mg, or 2 cups, of caffeine a day. This is because high levels of caffeine can result in babies having a low birth weight, which can increase the risk of health problems in later life, or even miscarriage.

Is coffee bad for you?
Risk of caffeine overdose
"There are relatively few deaths reported from caffeine overdose; however, prognosis largely depends on how quickly treatment is implemented," according to a 2021 study into caffeine toxicity.

Overdoses of caffeine in adults are very rare because it would be almost impossible to ingest the lethal amount over a short period of time.

In humans, blood concentrations of 80 to 100 micrograms/ml, or ingestion of 10 grams of caffeine is considered lethal - but that equates to drinking around 100 cups of coffee.

Experiencing an overdose of caffeine can have other complications, however. The study found that the "side effects of caffeine overdose can be profound" including seizure and neurologic changes, and, in severe cases, acute kidney injury, rhabdomyolysis, and even cardiac arrest.

Insomnia
Caffeine is predominantly used as a stimulant which offers short-term performance benefits, but the caffeine can linger for hours after you feel that initial boost, with the potential to lead to insomnia and restlessness.

Drinking coffee to stay awake at night can also lead to poorer sleep quality - from sleeplessness and anxiety to frequent night-time awakenings.

"[Coffee] still does have its properties acting in your system for many, many hours, even after you might not feel the stimulating effects of it," according to clinical professor Dr Deirdre Ann Conroy.

"People have very different sensitivities to caffeine and people who consume caffeine more often might respond differently to those who don't drink at all - but in general, our guideline is eight hours before going to bed, you should eliminate all caffeinated products."

Raised cholesterol
LDL (low-density lipoprotein) cholesterol is typically considered the “bad” cholesterol that causes the build-up of fatty deposits within arteries. Cardiologist Dr. Bruemmer, from the Cleveland Clinic, said that: “There are certain types of coffee where the low-density lipoprotein (LDL) cholesterol levels may be a little higher, like French press coffee, Turkish coffee and espresso.”

But he was quick to add that the amount that we typically consume, there’s very little impact of coffee on cholesterol, provided that it is in moderation.

Does coffee dehydrate you?
Caffeinated drinks, including coffee, may promote mild diuresis - the increased production of urine, but they don't appear to increase the risk of dehydration.

"Drinking caffeine-containing beverages as part of a normal lifestyle doesn't cause fluid loss in excess of the volume ingested," according to nutrition expert Katherine Zeratsky for the Mayo Clinic.

What are the health benefits of drinking coffee?
Reduced risk of death
It seems that drinking three cups of ground coffee a day, but not instant, could help people live longer, according to a 2022 study.

Almost half a million Britons enrolled in the UK Biobank study were divided by their coffee intake: those who drank none, up to three cups, and more than three cups a day.

The study revealed that moderate coffee drinkers, up to three cups a day, including those drinking decaffeinated coffee, were 12 per cent less likely to die over the study’s 11-year period.

They were also 17 and 21 per cent less likely to die of heart disease or stroke, respectively, according to the study from the Semmelweis University in Budapest and Queen Mary University of London.

Over the study period, 3.4 per cent of moderate drinkers died, compared to 3.7 per cent of coffee abstainers and four per cent of those drinking higher amounts of caffeine.

Among the coffee drinkers, a fifth preferred decaffeinated, a quarter drank ground beans and more than half opted for instant coffee.

Brightens mood
Experts tend to agree that caffeine stimulates your body's central nervous system and boosts the production of neurotransmitters like serotonin, dopamine, and noradrenaline - all of which can elevate your mood.

A 2021 consumer survey, which studied more than 5,000 adults across the UK, Italy, Finland, Germany and Poland, found that ingesting 75mg of caffeine every four hours improved seasonal affective disorder, and led to sustained mood improvement over the course of the day.

The study, funded by the Institute for Scientific Information on Coffee, said that as the hours of daylight decreased, respondents experienced increased feelings of sadness, became more anxious, found it harder to concentrate, lost motivation to exercise and saw a dip in sports performance.

However, in the review of existing research into lifestyle measures that improve mood, the study found that of those surveyed, 20 per cent of adults said they felt that their mood improved after drinking coffee.

A further 29 per cent said they felt more energised, while 21 per cent said it helped them feel more alert and to concentrate better.

Reduced risk of stroke and dementia
Drinking coffee (or tea) may be associated with a lower risk of stroke and dementia, according to a 2021 study of healthy individuals aged 50-74.

Researchers from Tianjin Medical University, China, studied 365,682 participants from the UK Biobank, recruited between 2006 and 2010 and followed them until 2020, who self-reported their coffee and tea intake at the outset.

Over the study period, 5,079 participants developed dementia and 10,053 experienced at least one stroke.

The study found that people who drank 2-3 cups of coffee or 3-5 cups of tea per day, or a combination of 4-6 cups of coffee and tea had the lowest incidence of stroke or dementia.

Drinking coffee was also associated with a lower risk of post-stroke dementia.

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