'Caffeine can be helpful to some people in moderation': Waking up to the health benefits of coffee 

Long seen as a treat to be consumed sparingly due to its high caffeine content, nutrient-rich coffee is increasingly recognised as a valuable support for health — from cardiac care to gut wellbeing and physical performance. We look at the latest research

William O'Connor: "It’s now known that the antioxidants in coffee can have benefits to health and even the caffeine it contains can be helpful to some people in moderation.”

For decades, coffee was considered an unhealthy crutch, a beverage we were urged to remove from our daily diets for the sake of our health. But as more evidence has emerged to show that coffee is beneficial to our mental and physical wellbeing — this month it was shown to protect against atrial fibrillation, a common heart rhythm disorder that causes rapid, irregular heartbeat — coffee finds itself rebranded as a wellness drink.

“Hundreds of tonnes of coffee are consumed every day by humans in Ireland and worldwide,” says William O’Connor, foundation professor of physiology in the University of Limerick School of Medicine, who hosts the Inside the Brain website. “It’s now known that the antioxidants in coffee can have benefits to health and even the caffeine it contains can be helpful to some people in moderation.”

As a plant food, coffee is also packed with more than 1,000 bioactive compounds, including tannins, oils, carbohydrates, and proteins, as well as antioxidants. It is also rich in polyphenols, especially chlorogenic acids, which have antioxidant and anti-inflammatory properties, supporting immune regulation and potentially helping fight off colds and viruses.

“As a plant-derived product, coffee does contain some plant fibres,” says O’Connor. This means it is even good for your gut. Last year, a study of more than 22,000 people published in Nature Microbiology identified 115 species of beneficial bacteria associated with drinking coffee. One key microbe, Lawsonibacter asaccharolyticus, was found to be 6-8% higher in coffee drinkers than in non-coffee drinkers.

As many coffee drinkers will testify, it can also be good for your mind. Researchers at the University of Warwick recently confirmed in the journal Scientific Reports that people who drink it regularly are usually in a better mood after a cup of coffee. 

O’Connor says the European Food Safety Agency recommends adults consume no more than 400mg of caffeine — that’s approximately four regular homemade cups of coffee — a day. “But you need to work out how it affects you as an individual,” he says.

Here’s what else you need to know about your daily brew:

Is coffee good for gut health?

Coffee is full of polyphenols, plant compounds that help feed the good bacteria in your gut microbiome, and it contains some fibre too. Last year, a study of more than 22,000 people by Zoe Nutrition, published in Nature Microbiology, identified 115 species of beneficial bacteria associated with coffee drinking. Drinking coffee increased a key beneficial microbe called Lawsonibacter asaccharolyticus. Also, it was six to eight times more abundant in coffee drinkers compared to non-drinkers.

A 2024 review by the University of Texas and the Liverpool School of Tropical Medicine, published in the journal Nutrients, also confirmed that moderate coffee intake — up to four cups a day — increased beneficial gut bacteria and reduced levels of harmful bacteria.

How does coffee help the heart?

Researchers at the University of California and the University of Adelaide showed that a cup of caffeinated coffee a day reduced A-Fib by 39%.

The recent study in JAMA showed that coffee can help to protect against atrial fibrillation (A-Fib), a common heart rhythm disorder that causes a rapid, irregular heartbeat and is associated with a risk of heart attacks and stroke. 

Researchers at the University of California and the University of Adelaide showed that a cup of caffeinated coffee a day reduced A-Fib by 39%. Gregory Marcus, a cardiologist at the University of California, San Francisco, and senior author of the paper, says “caffeine is also a diuretic, which could potentially reduce blood pressure and in turn lessen A-Fib risk”.

Several other compouds in coffee have anti-inflammatory properties that could have positive effects, he adds.

Does the way you brew coffee make a difference?

It’s not all good news for coffee beans and their effects on heart health. Two chemicals they contain — cafestol and kahweol — have been shown to raise levels of damaging LDL cholesterol in the blood. 

They remain present in any coffee that hasn’t been filtered, including moka pot, espresso, and cafetiere coffee, although filtering or using pods and metal capsules lined with filter paper will remove them. A study in Open Heart journal suggested that espresso, boiled, and plunger coffee all produced increases in cholesterol levels compared with filtered coffee.

Can coffee enhance your fitness?

According to the International Society of Sports Nutrition (ISSN), the biggest and most consistent gains come when coffee consumed before endurance activities such as cycling, swimming, and running.

Performance benefits mostly come from the caffeine in coffee, which according to a recent study in Sports Medicine, stimulates the central nervous system and blocks the release of adenosine, a chemical that promotes sleepiness and fatigue, leading to a stimulating effect. This prompts the release of hormones such as dopamine and epinephrine, which enhance mood and alertness.

Caffeine can also help muscles exert more force by mobilising the calcium needed to produce powerful contractions. According to the International Society of Sports Nutrition (ISSN), there are moderate benefits to drinking coffee (or taking caffeine from other sources) before activities like strength training, sprinting, and jumping, but the biggest and most consistent gains come when it is consumed before endurance activities such as cycling, swimming, and running.

How much coffee should you drink before a workout?

Amounts needed to produce a fitness boost vary according to individuals, but as a guide, the ISSN says you will need 3-6mg of caffeine per kilogram of your body weight. 

For someone weighing 657kg or around nine stone, that equates to 170mg of caffeine, which is about the amount in a double espresso or a large black coffee. 

A 2024 study on recreational runners with 5km times of slower than 25 minutes showed that those who took 300mg of caffeine, the equivalent of two double espressos, beforehand ran an average of 17 seconds faster over 5km than when they took no caffeine.

What are the benefits of decaf?

Removing caffeine from coffee involves soaking or steaming unroasted coffee beans until the caffeine dissolves or their pores open, allowing it to be extracted. Some decaffeination methods use water or liquid carbon dioxide, but others use synthetic chemicals such as ethyl acetate. 

Coffee aficionados believe the process damages the flavour of the coffee, although experts say the minuscule amounts of chemicals you get in a serving won’t have an impact on health. “The antioxidants will remain even when coffee is decaffeinated,” O’Connor says.

Should instant coffee be off the shopping list?

We often dismiss it as cheap and less tasty, but instant coffee is not without its virtues. In fact, research shows instant coffee has substantially higher concentrations of beneficial polyphenols and antioxidants than fresh coffee, and instant coffee contains almost twice as much soluble fibre as filter coffee, which could help some good gut bacteria to thrive if you drink it regularly. 

Some polyphenols can be lost in processing, but overall instant coffee still supports the growth of good gut bacteria. Studies at Coventry University’s school of life sciences showed that consuming approximately a dessert spoon of instant coffee granules dissolved in water 60 minutes before exercise can help people to work out harder for longer.

Are some beans better for us?

For gut health, a good-quality, lightly roasted arabica is probably the kindest brew.

The arabica bean has traditionally dominated the market, accounting for 60-70% of the world’s coffee consumption, but the more climate-resilient robusta bean is now making its mark. Most coffee chains use a blend of both beans, but what should you choose if you buy your own? 

A study in the European Food Research and Technology journal found that the robusta bean contains up to double the amount of caffeine as the arabica bean and while robusta beans have been shown to contain double the amount of antioxidants, the difference diminished after intense roasting. For gut health, a good-quality, lightly roasted arabica is probably the kindest brew.

How strong is my coffee?

How coffee is prepared and the size of a serving both influence how much caffeine you will consume. Typically, a single shot espresso contains 30-180mg caffeine, a filter or brewed coffee 95-270mg per serving, a coffee pod provides 40-200mg, and a cup of instant coffee 30-90mg caffeine. 

Be aware that the 1-10 strength rating that appears on many packets of coffee denotes the strength of roast rather than caffeine content. The higher the number, the darker the roast and stronger the flavour. A light roast with a 1-3 rating might well contain as much caffeine as a punchier, dark roasted 7-8 coffee.

Is it safe for anyone to drink?

The Irish Heart Foundation says that some people are more sensitive than others to the effects of caffeine and there are “certain groups of the population where these recommendations would differ”. 

For example, pregnant women should have no more than 200mg of caffeine per day throughout their pregnancy. Also, always check with your doctor before consuming coffee alongside prescribed drugs. And, since caffeine is a stimulant, drinking coffee too close to bedtime can adversely affect sleep.

“We all have different tolerance levels to caffeine, so not every person responds in the same way to coffee intake,” O’Connor says. “Don’t assume that because someone in your household can drink four to five cups that you can do the same.”