Compared with people who did not drink coffee, morning coffee drinkers were 31 percent less likely to die of heart disease and 16 percent less likely to die prematurely of any cause. However, all-day coffee drinkers didn’t have those same reductions — they had the same risk for heart disease death and early death as the no-coffee group.
This is the first-ever study that looked at not only how much coffee people drink, but what time of day they are drinking it and health outcomes, says lead author Lu Qi, MD, PhD, a professor at the Celia Scott Weatherhead School of Public Health and Tropical Medicine at Tulane University in New Orleans.
“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,” he says.
2 or 3 Cups of Morning Coffee Were the ‘Sweet Spot’
Most prospective studies have found that moderate coffee drinking — about 200 to 300 milligrams of caffeine a day, or about two to three 12-ounce cups of coffee — is linked with lower risks of heart attack, stroke, and type 2 diabetes.
The authors of the new study aimed to take the current evidence one step further: Does the time of day when people drink their coffee have any impact on heart health?
The study included over 40,000 adults who were part of the National Health and Nutrition Examination Survey (NHANES) between 1999 and 2018. Participants were asked about all the food and drink they consumed on at least one day, including whether they drank coffee, how much, and when.
The survey also included a subgroup of about 1,400 people who were asked to complete a detailed food and drink diary for a full week.
Researchers linked this information with records of deaths and cause of death over a period of close to 10 years.
The study defined “morning coffee drinking” as occurring between 4 a.m. and 11:59 a.m.
Close to 36 percent of people in the study were morning coffee drinkers, 16 percent drank coffee throughout the day, and 48 percent were not coffee drinkers.
Morning coffee drinkers benefited from the lower risks whether they were moderate drinkers (two to three cups) or heavy drinkers (more than three cups). Light morning drinkers (one cup or less) had a smaller decrease in risk.
This is a well done and fascinating study, says David Kao, MD, an associate professor of cardiology at the University of Colorado Anschutz Medical Campus, who was not involved in the research. Dr. Kao’s research has included investigations into the health effects of coffee drinking.
“Many of us who have published in this area have noted that robust observational/real-world studies are needed to answer questions like ‘why’ and ‘how’ this association works, and this is probably the best such next-generation paper I have seen,” he says.
The concentration of benefit in morning coffee drinkers is certainly valuable to discussing this issue with patients, says Kao.
“It’s reassuring that several patterns observed previously — such as an apparent ‘sweet-spot’ around two to three cups of coffee per day — suggest that these findings probably are relevant to prior studies. Validation in large independent cohorts really strengthens the arguments,” he says.
Why Wouldn’t Drinking Coffee Later in the Day Have the Same Benefits?
Because the study was observational, it doesn’t explain why drinking coffee in the morning reduces the risk of death from cardiovascular disease or why all-day coffee drinking didn’t have the same benefits in risk reduction.
“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,” says Dr. Qi.
The authors raise very good points on the disruption of the human circadian rhythm or sleep cycle with later coffee consumption, says Nishant Shah, MD, an assistant professor of medicine at Duke University School of Medicine in Durham, North Carolina, who was not involved in the study.
“It is well known that good sleep hygiene leads to better health. The authors also nicely note that coffee does contain some anti-inflammatory properties that work best in the morning times [rather than at] later times,” says Dr. Shah.
But when considering the findings, keep in mind that any observational study can’t establish a causal relationship, just a suggestion of one, he says.
“There may also be other factors that influenced the results of the study. For example, early morning coffee drinkers may have better overall health and lifestyle habits than those who drink coffee throughout the day,” says Shah.
The study also may be subject to recall biases based on the self-reported nature of many of the variables, he says.
“However, the authors did a great job in trying to limit as many factors as possible that could influence the results,” says Shah.
Should You Stop Drinking Afternoon Coffee?
Although the findings are compelling, there isn’t enough data to recommend that people confine their coffee drinking to the morning — experts still aren’t sure that the reduced risk is connected to the timing or other factors, says Kao.
“It’s also worth noting that all-day drinkers don’t have a worse risk compared with non–coffee drinkers, just not a significantly reduced risk,” he says.
This would suggest that if coffee throughout the day is an important part of someone’s life, and it isn’t causing any harm, there’s no reason to recommend against it, says Kao.
Qi agrees, saying, “More studies are needed to validate our findings in different populations before making recommendations.”
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