Media playback is unsupported on your device Media caption How much coffee is good for you? - in 90 secs

Drinking a few cups of coffee a day may help people avoid clogged arteries - a known risk factor for heart disease - Korean researchers believe.

They studied more than 25,000 male and female employees who underwent routine health checks at their workplace.

Employees who drank a moderate amount of coffee - three to five cups a day - were less likely to have early signs of heart disease on their medical scans.

The findings reopen the debate about whether coffee is good for the heart.

Heart effects

There is a lot of confusion when it comes to the effect of coffee on heart health.

Image copyright Science Photo Library Image caption In heart disease, the arteries supplying the heart muscle can become blocked

Some studies have linked consumption to heart risk factors, such as raised cholesterol or blood pressure, while others suggest the beverage may offer some heart protection.

But there is no conclusive evidence either way, and the latest research from South Korea, which is published in the journal Heart, only adds to the discussion.

Unexplained link

In the study, the researchers used medical scans to assess heart health.

Specifically, they were looking for any disease of the arteries supplying the heart - the coronary arteries.

More research is needed to confirm these findings and understand what the reason is for the association Victoria Taylor of the British Heart Foundation

In coronary heart disease, the coronary arteries become clogged by the gradual build-up of fatty material within their walls.

The scan the researchers used looks for tiny deposits of calcium in the walls of the coronary arteries to provide an early clue that this disease process may be occurring.

None of the employees included in the Korean study had outward signs of heart disease, but more than one in 10 of them were found to have visible calcium deposits on their scans.

The researchers then compared the scan results with the employees' self-reported daily coffee consumption, while taking into account other potential heart risk factors such as smoking, exercise and family history of heart problems.

People who drank a few cups of coffee a day were less likely to have calcium deposits in their coronary arteries than people who drank more than this or no coffee at all.

The study authors say more research is needed to confirm and explain the link.

Coffee contains the stimulant caffeine, as well as numerous other compounds, but it's not clear if these might cause good or harm to the body.

Victoria Taylor of the British Heart Foundation said: "While this study does highlight a potential link between coffee consumption and lower risk of developing clogged arteries, more research is needed to confirm these findings and understand what the reason is for the association.

"We need to take care when generalising these results because it is based on the South Korean population, who have different diet and lifestyle habits to people in the UK."

How much caffeine?

Image copyright Phillip Hayson/SCIENCE PHOTO LIBRARY

In the US, experts say up to 400mg a day appears to be safe for most healthy adults

There is no recommended daily upper limit for caffeine consumption in the UK, except for pregnant women

If you're pregnant, you should limit the amount of caffeine you have to 200mg a day - equivalent to two mugs of instant coffee

one mug of instant coffee: 100mg

one mug of filter coffee: 140mg

one mug of tea: 75mg

one can of cola: 40mg

an espresso contains about 50mg of caffeine

Coffee shop caffeine levels vary widely

Source: NHS Choices