(CNN) — Drinking coffee has repeatedly been linked with better heart health and prolonged life. But the benefits of coffee consumption could depend on when you drink it, new research has found.
Limiting coffee intake to the morning, it turns out, may be best — and that seems to be regardless of the amount consumed and other potentially influential factors, according to a study published Tuesday in the European Heart Journal.
“This is the first study testing coffee drinking timing patterns and health outcomes,” said lead author Dr. Lu Qi, HCA Regents Distinguished Chair and professor at Tulane University’s Celia Scott Weatherhead School of Public Health and Tropical Medicine in New Orleans, in a news release. “We don’t typically give advice about timing in our dietary guidance, but perhaps we should be thinking about this in the future.”
Most past research investigating participants’ coffee intake over time have found moderate levels of coffee consumption may be associated with lower risks of type 2 diabetes, cardiovascular diseases and premature death, according to the latest study. But scientific evidence of whether factors such as genetics, amount consumed or added sweeteners affect these relationships has been inconsistent or, at times, controversial, the authors said.
The authors studied the dietary and health data of 40,725 adults age 18 and older from the National Health and Nutrition Examination Survey conducted from 1999 to 2018. During 10 cycles over the years, those participants provided details of their dietary intake from the previous day. The authors also included a subgroup of 1,463 adults, from both the women’s and men’s versions of the Lifestyle Validation Study, who had completed at least one weeklong dietary record.
Both caffeinated and decaffeinated coffee were included, and timing was categorized in three periods: morning (from 4 a.m. to 11:59 a.m.), afternoon (from 12 p.m. to 4:59 p.m.) and evening (from 5 p.m. to 3:59 a.m.).
The researchers identified two patterns of timing of consumption: morning and all day. By the end of the median follow-up period of nearly 10 years, there were 4,295 deaths from all causes, 1,268 from cardiovascular disease and 934 from cancer.
Compared with people who weren’t coffee drinkers, having coffee only in the morning was associated with a 16% lower risk of premature death from any cause and a 31% lower risk of dying from cardiovascular disease. Those who tended to drink coffee all day didn’t have a reduction in risk. These findings remained even after the authors took into account confounders such as sleep hours, age, race, ethnicity, sex, family income, education, physical activity levels, a dietary score, and health conditions such as diabetes, hypertension and high cholesterol.
For morning coffee drinkers, the amount of caffeinated or decaffeinated coffee consumed didn’t matter, either — whether they drank less than one or more than three cups of coffee daily. Having done so in the morning was still better than other patterns in terms of mortality risk.
“The study was observational, meaning that it wasn’t an experiment setting, (which) is the gold standard,” said Vanessa King, a registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics who wasn’t involved in the study, via email.
The nature of the study also means it only establishes an association, not a causal relationship between morning coffee drinking and early death risk. But the findings are “meaningful as the leading cause of death in America is cardiovascular diseases,” King added.
Why timing could matter
Dr. David Kao, who wasn’t involved in the research, found the study to be “fascinating” and one of the best investigations on this topic in years, he said.
“Highlights include using a machine learning-style method to categorize coffee drinking patterns, and validation of findings in (more than one) external data source which are distinct from the primary source, which greatly reduces the likelihood of an accidental/false positive finding,” Kao, the Jacqueline Marie Schauble Leaffer Endowed Chair in Women’s Heart Health at the University of Colorado Anschutz, said via email.
However, the study has a few other shortcomings: For one, recollections of dietary intake are subject to inaccuracies or biases, and they don’t account for long-term habits, the authors said.
Secondly, even though the authors considered multiple confounders, it’s possible there were others that couldn’t be completely ruled out, they said.
The team “could not exclude the possibility that the morning-type coffee drinking pattern is a marker for an overall healthy lifestyle,” according to the study. “For example, morning-type coffee drinkers may be more willing to exercise and eat non-ultra-processed foods.”
Additionally, genetic information wasn’t available, so the authors were unable to examine any possible effect of genetically determined caffeine metabolism rates.
A possible explanation for the findings “is that consuming coffee in the afternoon or evening may disrupt circadian rhythms and levels of hormones such as melatonin,” Qi said. Low levels of melatonin have been linked with higher levels of blood pressure and oxidative stress, and greater cardiovascular disease risk.
Coffee also contains antioxidants that reduce inflammation in the body by neutralizing free radicals that may increase the risk of cardiovascular disease, King said. Free radicals, unstable molecules from environmental sources such as cigarette smoke or pesticides, can harm cells.
Some inflammatory markers in the blood have their own clocks, the authors said, and they are typically highest in the morning — so “the anti-inflammatory effect of a pattern of coffee consumption concentrated in the morning may be more beneficial than that of a pattern … spread across morning, afternoon and evening.” That applies to both caffeinated and decaf coffee consumption.
Adjusting coffee intake
If you want to start restricting your coffee intake to the morning but are having trouble, consider whether you’re regularly getting enough quality rest, King said. Seeing a sleep specialist to find out whether you have a condition, such as sleep apnea, disturbing your rest could also be useful, Kao said.
You can also begin with diluting your daytime servings and accompanying them with water for hydration, King said — which can also help you feel more awake.
READ MORE: 6 ways to wake up without coffee
Getting your thyroid, vitamin D and iron levels tested can help you determine whether exhaustion is stemming from something more serious, said Sue-Ellen Anderson-Haynes, a registered dietitian nutritionist and spokesperson for the Academy of Nutrition and Dietetics.
If you don’t drink coffee and think you could gain from adding it to your routine, first “look at the bigger picture,” said Anderson-Haynes, who wasn’t involved in the study. “Are you living an overall physically active, balanced, sustainable and healthy diet and lifestyle?”
Until more evidence is provided about when to drink coffee, she added, follow your doctor or dietitian’s recommendation on caffeine intake.