11 February 2025

“Drink your coffee, but do so in the morning,” writes Prof Thomas Lüscher in the European Heart Journal, commenting on a major new study on coffee consumption.

The study, ‘coffee drinking timing and mortality in US adults’ by X Wang et al, included more than 40,000 adults over a 20-year period.

It concludes that drinking coffee in the morning “may be more strongly associated with a lower risk of mortality than drinking coffee later in the day”.

In his editorial Prof Lüscher, co-leader of the KHP Cardiovascular Clinical Academic Group, stated that moderate coffee consumption is inversely associated with the risk of heart failure, with the largest effect noted with four servings a day. Tom Smurthwaite spoke to him about the study to find out more.

The X Wang et al study suggests we should be drinking four cups of coffee in the morning, why is this?

This is the crucial question. The short answer is that we don’t know for sure, but there are many good explanations. Firstly, if you drink coffee all day long then the diurnal rhythm [the biological rhythm that is synchronised with the daylight cycle] of our body is disturbed, in particular your sleep, an important predictive factor for clinical outcomes. The optimal sleep duration is around eight hours.

Most inflammation in the body happens in the morning, and coffee has anti-inflammatory effects so maybe that’s particularly beneficial.

Another aspect is that occasional coffee drinkers have more side effects, like palpitations and an increase in blood pressure. If you regularly drink four cups of espresso a day over time you’re down-regulated and get fewer effects – what we call tachyphylaxis. These are major aspects.

Obviously there are confounders, because people who drink coffee all day long are more likely to smoke and have behaviour that’s not optimal for lifestyle. One has to consider this when interpreting the results.

The Wang et al study was huge and they just asked patients when they drank their coffee as there is a limitation to what you can do with such large cohorts. The big advantage is that you have enough events to make a statement. The disadvantage is that you can’t ask too many details because people get annoyed and then you don’t get the data. One has to be realistic but the findings are truly interesting.

In your editorial you write ‘moderate, but regular coffee drinking attenuates the massive sympathetic activation in heart failure and as such may provide some protection’, please can you explain this?

In heart failure the body tries to give an extra kick to the failing heart through the sympathetic nervous system - the fight-or-flight reaction, but is commonly too much of a good thing and indeed associated with worse outcomes. Through our studies we found that coffee surprisingly attenuates this response and this may be protective in patients with heart failure.

Coffee – even decaffeinated – is a soup of numerous substances, many of which have not been well characterised. So, besides caffeine, there many other compounds involved that require characterisation.

You mentioned that drinking both caffeinated and non-caffeinated coffee has the same outcome, do we know what ingredient in coffee is having the effect?

We were indeed very surprised. Of course when you infuse caffeine you get palpitations and an increase in blood pressure but there are other substances that cause similar effects that have not been identified well enough.

Research in nutrition is more difficult than if you’re investigating a pill, where you have only one compound. If you investigate coffee, chocolate, or alcoholic drinks, there are other substances in there that may be relevant.

In coffee the caffeine has been well characterised, but we haven’t identified the biological effects of many other substances.

How about having milk and sugar in your coffee?

Sugar is basically bad. We get enough glucose in our body when we eat, so if you add additional glucose, it increases the risk of first obesity and then diabetes. Our ancient tribes didn’t have sugar or salt, they got enough to survive on from the fruit, vegetables and meat they were eating. You should refrain from adding salt to a serving from a health point of view. And adding milk to coffee is unlikely to have health effects, although we haven’t investigated that as such and it does contain fat.

Are there any similar studies on tea, how much to drink, when, and any positive effects?

This is a very important question in the UK and to my knowledge I haven’t seen any comparable studies. We have worked in the laboratory on some of the components in tea and a few of them were protective. But I’m not aware of a large cohort like the Wang coffee study. In England you often drink it with milk, but I think that disturbs the taste terribly.

Controversial!

Of course, as taste is in general.  

In conclusion

The Wang et al study is huge and has two advantages – first of all the large number of patients and secondly they also looked at a smaller cohort for confirmation. This is very reassuring for the evidence.

They had a granular questionnaire on their dietary behaviour and were able to dissect what they consumed and when. I think this is probably the best evidence we can have because it’s difficult to run a randomised trial as nobody wants to be in the placebo group.

In my editorial I tried to provide some explanations of these initially surprising findings. The novelty of this paper is the different daytime effect of coffee drinking and I think that makes it a very interesting publication.  

Prof Thomas Lüscher is a consultant cardiologist and director of research, education and development working at both Royal Brompton and Harefield hospitals. He is active on X and has his own YouTube channel.

To learn more about the KHP Cardiovascular Clinical Academic Group, visit the webpage here.