How much coffee is too much? Scientists decode

Drinking six or more cups of coffee a day can be harmful to your health, increasing the risk of heart disease by up to 22 per cent, a study claims.

A morning coffee is essential for many people looking to kick-start their day.

While the humble coffee may be a vital feature of the daily grind, researchers from the University of South Australia wondered how much caffeine is too much.

They investigated the association of long-term coffee consumption and cardiovascular disease, finding the point at which excess caffeine can cause high blood pressure, a precursor to heart disease.

According to the World Health Organization (WHO), cardiovascular disease is the leading cause of death, yet one of the most preventable.

This is the first time an upper limit has been placed on safe coffee consumption and cardiovascular health, according to the study published in The American Journal of Clinical Nutrition.

"Coffee is the most commonly consumed stimulant in the world -- it wakes us up, boosts our energy and helps us focus -- but people are always asking 'How much caffeine is too much?'," said Elina Hypponen, a professor at the University of South Australia.

"Most people would agree that if you drink a lot of coffee, you might feel jittery, irritable or perhaps even nauseas -- that's because caffeine helps your body work faster and harder, but it is also likely to suggest that you may have reached your limit for the time being," Hypponen said.

"We also know that risk of cardiovascular disease increases with high blood pressure, a known consequence of excess caffeine consumption," she said.

In order to maintain a healthy heart and a healthy blood pressure, people must limit their coffees to fewer than six cups a day, researchers said.

Based on the data, six was the tipping point where caffeine started to negatively affect cardiovascular risk, they said.

Using UK Biobank data of 347,077 participants aged 37-73 years, the study explored the ability of the caffeine-metabolising gene (CYP1A2) to better process caffeine.

The researchers identified increased risks of cardiovascular disease in line with coffee consumption and genetic variations.

Hypponen said that despite carriers of the fast-processing gene variation being four times quicker at metabolising caffeine, the research does not support the belief that these people could safely consume more caffeine, more frequently, without detrimental health effects.

"An estimated three billion cups of coffee are enjoyed every day around the world," Hypponen said.

"Knowing the limits of what's good for you and what's not is imperative," she said.