Researchers wanted to assess whether the time of day people drink coffee has any impact on their health.

They studied more than 40,000 adults in the US taking part in long-term studies examining health, nutrition and lifestyle.

They found two distinct patterns of coffee drinking - those who drink coffee before midday and those who drink coffee all day.

More than a third (36 per cent) of those taking part in the study were deemed to be morning coffee drinkers, while around 14 per cent were all-day coffee drinkers.

The research team, led by experts from Tulane University in the US, tracked people in the study for almost a decade.

During the follow-up period, some 4295 people taking part in the study died.

After taking into account various factors, the researchers found morning coffee drinkers were 16 per cent less likely to have died compared with those who drank no coffee.

And they were 31 per cent less likely to have died from heart disease.

There was no reduction in risk for all-day coffee drinkers compared with those who did not drink any coffee.

The researchers said higher coffee intake amounts were "significantly" associated with a lower risk of death, but only among people who drank coffee in the morning compared with those who drank coffee all day.

"Drinking coffee in the morning may be more strongly associated with a lower risk of mortality than drinking coffee later in the day," they wrote in the European Heart Journal.

Lead author Dr Lu Qi, from Tulane University in Louisiana, said: "Research so far suggests that drinking coffee doesn't raise the risk of cardiovascular disease, and it seems to lower the risk of some chronic diseases, such as type 2 diabetes."

"Given the effects that caffeine has on our bodies, we wanted to see if the time of day when you drink coffee has any impact on heart health."

"This is the first study testing coffee drinking timing patterns and health outcomes.

"Our findings indicate that it's not just whether you drink coffee or how much you drink, but the time of day when you drink coffee that's important. We don't typically give advice about timing in our dietary guidance, but perhaps we should be thinking about this in the future.

"This study doesn't tell us why drinking coffee in the morning reduces the risk of death from cardiovascular disease.

"A possible explanation is that consuming coffee in the afternoon or evening may disrupt circadian rhythms and levels of hormones such as melatonin. This, in turn, leads to changes in cardiovascular risk factors such as inflammation and blood pressure."

Similar findings were observed among those who drank caffeinated coffee or decaffeinated coffee either in the morning or throughout the day.

With AAP.