Caffeine is a stimulant and the most commonly used drug in the world. Data from a survey on attitudes towards coffee conducted in Australia in 2022 showed that coffee culture is deeply embedded in the Australian lifestyle, with coffee being the main mode of caffeine consumption for over half of the people surveyed. 

Amid myths and controversy about whether caffeine is good or bad for us, evidence suggests that moderate coffee consumption can bring both benefits and risks.

Caffeine is considered to be both a drug and a food additive. The widely accepted recommendation is a maximum intake of 400mg a day - about 4 or 5 cups of coffee. This amount is not associated with negative effects. There is no set limit for children, but the consumption of caffeine and other stimulants by children and adolescents is discouraged by medical professionals.

Seventy-five per cent of survey respondents claimed that they enjoy at least one cup of coffee a day. Twenty-eight per cent of Australians reported that they enjoy three or more cups of coffee a day. 

Benefits can include increased alertness, energy, and concentration, so every day, millions of people consume caffeine to increase wakefulness, alleviate fatigue, and improve concentration and focus. 

Caffeine features in tea, coffee, and chocolate, and it is regularly added to gum, jellybeans, waffles, water, syrup, marshmallows, sunflower seeds, and other snacks. Caffeine occurs naturally in the leaves, seeds, or fruit of more than 60 plant species, including coffee beans, tea leaves and buds, kola nuts, cacao beans, guarana seeds, and yerba mate leaves.

Caffeine may have some wide-reaching health benefits, but not all of these have been fully confirmed by definitive research, including:

• Easing certain types of headaches or migraines
• Boosting weight loss or preventing weight gain
• Increasing attention and alertness
• Improving physical performance
• Enhancing some thinking skills and slowing mental decline
• Reducing the risk of developing Alzheimer’s disease
• Boosting long-term memory
• Decreasing the risk of cirrhosis
• Helping protect people from an eye disorder known as blepharospasm
• Potentially protecting the lens of the eye against damage that could lead to the formation of cataracts
• Guarding against certain skin cancers
• Lowering the risk of developing kidney stones
• Lowering the risk of death from oral cancer, and reducing the risk for other cancers (endometrial, prostate, head and neck, breast, liver)
• Lowering the risk of stroke
• Lowering the risk of developing type 2 diabetes.

In some types of headaches, the blood vessels in the brain dilate or swell, expanding into the surrounding tissues, which triggers pain. Consuming caffeine, which narrows the vessels, can ease or even reverse some headache pain. Ironically, a sudden lack of daily caffeine can cause a headache.

Caffeine may boost weight loss or prevent weight gain by suppressing the appetite and temporarily reducing the desire to eat, and by stimulating thermogenesis, so the body generates more heat and energy from digesting food. Weight loss products that are marketed as thermogenic may contain caffeine and ephedra, or ephedrine. Research has not confirmed long-term results.

In prescription and over-the-counter medicines, caffeine is used to treat tiredness and drowsiness, and to improve the effect of some pain relievers. It belongs to a group of medicines called central nervous system stimulants. A 75mg serving of caffeine can increase attention and alertness, and a 160-600mg dose may improve mental alertness, speed reasoning, and memory. However, caffeine is not a substitute for sleep and should not regularly be used for this purpose. If overused it can also lead to insomnia and headaches.

Caffeine can improve physical performance during endurance exercise. The Australian Institute of Sport recognises that caffeine can increase endurance performance, endurance capacity, and reduction in perceived exertion. However, the effects on short-term, high-intensity exercise remain inconclusive.

Studies have suggested that drinking coffee may help enhance some thinking skills and slow the mental decline that comes with age. However, more research is needed to confirm this. 

Research has found that lifelong caffeine consumption may reduce the risk of developing Alzheimer’s disease. Studies have also reported that people with higher coffee consumption have a lower risk of Parkinson’s disease.

Research from Johns Hopkins University in Baltimore suggests that a dose of caffeine after a learning session may help boost long-term memory.

It has been suggested that caffeine enemas may help prepare the colon for an endoscopy or colonoscopy by supporting the excretion of bile through the colon wall. Advocates claim that a caffeine enema increases the levels of glutathione, an antioxidant, and so supports the natural processes of detoxification in the liver. However, at this time there is little evidence to support this theory.

Coffee consumption may help decrease the risk of cirrhosis and slow the rate of disease progression in hepatitis C infection. Observational studies have found that coffee may have protective benefits for people with hepatocellular cancer.

There is some evidence that caffeine may help protect people from an eye disorder known as blepharospasm. This condition, caused by abnormal brain function, makes people blink incessantly and can leave them functionally blind.

Researchers have found that caffeine may help protect the lens of the eye against damage that could lead to the formation of cataracts.

Some scientists have suggested that caffeine may guard against certain skin cancers. One team found that caffeine applied directly to the skin of mice helped prevent damaging ultraviolet light from causing skin cancer. Others have linked the consumption of three cups of coffee a day with a 21 percent lower risk of developing basal cell carcinoma in women, and a 10 percent lower risk in men, compared with drinking less than one cup per month.

A study of 217,883 participants analysed the association between caffeine intake and the risk of developing kidney stones. Those who consumed more caffeine had a lower risk of developing kidney stones.

In a study of 968,432 men and women, participants who drank more than four cups of coffee a day had a 49 per cent lower risk of death from oral cancer, compared with those who drank no coffee at all or only an occasional cup.

Other possible cancer-related benefits include:

• A lower risk of endometrial cancer
• A reduced risk of prostate cancer
• Protection against head and neck cancer
• Protection against the recurrence of breast cancer.

Data for 34,670 women in Sweden without a history of cardiovascular disease indicated that women who drank more than one cup of coffee per day had a 22-25 percent lower risk of stroke compared with women who drank less.

Low or no coffee drinking appeared to be linked to an increased risk of stroke.

One longitudinal study found that participants who increased their coffee intake by more than one cup a day over a four-year period had a 1 percent lower risk of developing type 2 diabetes compared with people who did not change their intake. People who lowered their daily consumption by more than one cup of coffee showed a 17 per cent higher risk for type 2 diabetes. 

A study published in Diabetes Care in 2004 linked high coffee consumption over a period of four weeks with increased fasting insulin concentrations. However, the reasons for the link were unclear. It may be due to lowered insulin sensitivity, meaning the body does not use the insulin produced efficiently. The team called for more investigation before asserting that high coffee consumption lowers the risk for type 2 diabetes.

These prospective benefits stated, it is important to note that high consumption of caffeine may not be healthy. It may have a negative impact on pregnancy, fertility, glucose control, and other aspects of health.

The recent trend of adding caffeine to drinks and snacks that do not naturally contain it has raised new concerns, such as the question of energy drinks, and whether caffeine overdose could occur. Having said that, caffeinated energy drinks are unlikely to be hazardous unless consumed with alcohol.

Caffeine is unsafe when used in very high doses, as it can cause irregular heartbeat and even death. Products with very concentrated or pure caffeine have a high risk of being used in doses that are too high, which is why pure and highly concentrated caffeine food products (including pure caffeine powders) are banned from retail sale in Australia.

Despite its widespread use and numerous benefits, caffeine is a powerful substance that should be consumed with caution. Moderation is key, as excessive intake can lead to adverse health effects. Understanding the balance between benefits and risks can help individuals make informed choices about their caffeine consumption. As research continues to unfold, staying updated on the latest findings will ensure that we maximise the positive effects of caffeine while minimising potential harms.