When we wake up in the morning, many of us reach for a coffee to kick-start our day. According to the International Coffee Organization, approximately 1.6 billion cups of coffee are consumed worldwide every day.
The US Food and Drug Administration (FDA) state that the average amount of caffeine consumed in the US is approximately 300 mg per person per day - the equivalent to between two and four cups of coffee. This is considered to be a moderate caffeine intake, which according to many studies, can promote a variety of health benefits.
But some studies claim otherwise, even suggesting that one or two cups of coffee a day may negatively impact our health. So, what are we to believe?
We analyze the potential health benefits, as well as the negative side effects of caffeine consumption.
Caffeine is a natural stimulant
The main ingredient in coffee is caffeine - a compound that naturally derives from over 60 different plant sources, including coffee beans, tea leaves, cacao seeds and cola nut seeds.
According to the University of Michigan Health Service, the stimulating effects of caffeine can start as early as 15 minutes after consumption and last up to 6 hours.
Other than coffee, caffeine is commonly consumed through tea, soft drinks - particularly energy drinks - and chocolate. It is also found in some prescription and non-prescription drugs, such as cold, allergy and pain medication.
Caffeine's potential health benefits
As well as its stimulating effects, caffeine has been heralded for providing an array of health benefits.
Some studies have suggested that drinking three or four cups of coffee a day may reduce the risk of liver, mouth and throat cancer.
Last year, Medical News Today reported on a study suggesting that consuming three cups of coffee a day may reduce the risk of liver cancer by 50%, while another study suggests that drinking four cups a day could halve the risk of mouth and throat cancer.
Caffeine consumption has also been associated with positive effects on the brain.
Last year, a study from the Harvard School of Public Health suggested that drinking between two and four cups of coffee a day may reduce suicide risk in adults, while more recent research found that ingesting 200 mg of caffeine each day may boost long-term memory.
Caffeine: the 'socially acceptable psychoactive drug'
With so much research claiming that caffeine consumption can benefit our health, and considering the number of products that contain the stimulant, it is no wonder caffeine consumption is so widespread.
But Steven E. Meredith, postdoctoral research fellow at The Johns Hopkins University School of Medicine, told Medical News Today that, perhaps due to widespread consumption, many of us forget that caffeine is a psychoactive substance - a drug that crosses the blood-brain barrier to stimulate the central nervous system.
"Unlike most other psychoactive substances, caffeine use is socially acceptable, and the drug is widely used. In fact, caffeine is the most commonly used psychoactive substance in the world.
Moreover, the vast majority of caffeine consumers use the substance regularly without apparent harm. These factors likely contribute to the perspective that caffeine is a benign substance that everyone can use without suffering any negative consequences."
The negative effects of caffeine consumption
But of course, there can be negative consequences from caffeine consumption, particularly if ingested in high doses.
However, previous research has linked even moderate amounts of caffeine to negative health effects.
Last year, Medical News Today reported on a study suggesting that consuming 300 mg of caffeine a day during pregnancy may increase the risk of low birth weight babies, while other research suggests that drinking four cups of coffee a day may increase the risk of early death.
Effects of caffeine vary from person to person
But Meredith told us that the effects of caffeine can vary in each individual, which may explain why there are mixed messages surrounding whether caffeine is good or bad for us.
For example, he said that individuals with anxiety disorders are more susceptible to the anxiogenic effects of the compound.
Cigarette smokers can metabolize caffeine twice as fast as non-smokers.
"Caffeine can also metabolize at different rates among individuals for various reasons. For example, cigarette smokers metabolize caffeine twice as fast as non-smokers," he added.
"However, caffeine metabolism is slower among infants, pregnant women and individuals with liver disease. In addition, some medications slow caffeine metabolism, which may increase the risk for caffeine intoxication. But the effects of caffeine also vary simply because we're all different."
Rob M. Van Dam, adjunct associate professor of the Department of Nutrition at the Harvard School of Public Health, told Medical News Today that the effects of caffeine are dependent on each person's genetic characteristics and lifestyle factors.
"Thus, some people may have difficulty sleeping or experience tremors or stress with relatively low caffeine intakes and it is useful to be aware of these symptoms and reduce caffeine intake if these occur," he added.
Caffeine addiction and withdrawal
Given the positive effects caffeine can have as a stimulant, Meredith told Medical News Today that for some people, this can result in caffeine addiction:
"Caffeine activates many of the same behavioral and neuropharmacological mechanisms that are activated by other reinforcers, including other drugs of abuse.
And, like many other reinforcers, caffeine is associated with various positive subjective effects like increased wellbeing, sociability, and feelings of energy and alertness. For this reason and others, a small percentage of the population develops caffeine use disorder."
He said that some people can become physically dependent on caffeine, with absence or reduction of coffee consumption in these individuals resulting in caffeine withdrawal.
"Dependence can become so strong for some individuals that they're unable to reduce consumption despite knowledge of recurrent physical or psychological problems associated with continued use," Meredith added.
Kids and adolescents 'should avoid caffeine consumption'
Meredith said that based on the negative side effects caffeine consumption can have, doctors should be discussing caffeine use with their patients to determine whether they are ingesting safe levels of the stimulant.
Furthermore, he warned that this is particularly important for children and adolescents.
Pediatricians recommend that children should steer clear from caffeine, often found in soft drinks.
The majority of pediatricians recommend that this population should avoid caffeine consumption, particularly since it is unknown as to how excessive caffeine intake impacts the developing brain.
"Notably, caffeine interferes with sleep, and sleep plays a critical role in learning. Some laboratory research suggests that caffeine interferes with sleep and learning among adolescent rodents, which, in turn, hinders normal neurological development that is noticeable into adulthood," said Meredith.
"Some psychologists are also concerned that a pattern of caffeine use or abuse among young people may lead to subsequent problematic drug and alcohol use."
The FDA clearly hold a similar view to pediatricians. In May last year, the organization announced it would be investigating the safety of caffeine in food products, particularly products aimed at children and adolescents.
The FDA are concerned that many food and drink products, such as jelly beans, waffles, syrup and chewing gum, now have caffeine added to them to enhance their stimulating effect.
Michael R. Taylor, deputy commissioner for foods and veterinary medicine at the FDA, said:
"We're particularly concerned about children and adolescents and the responsibility FDA and the food industry have to protect public health and respect social norms that suggest we shouldn't be marketing stimulants, such as caffeine, to our children."
Meredith told us that studies have shown high caffeine intake may also produce negative side effects in pregnant women and individuals with heart conditions or anxiety disorders.
However, he added that the majority of us consume caffeine in moderation without any harmful side effects, so healthy adults should not be overly concerned.
"But we should be mindful that when we consume caffeine, we are consuming a psychoactive substance that can cause or exacerbate some health problems," he cautioned.