A cup of coffee a day could keep heart failure at bay, research suggests.
Many rely on lattes, mochas or cappuccinos to get through the morning, with few subjects inciting as much health debate as caffeine.
After combining three large studies, scientists from the University of Colorado reported drinking one or more cups of caffeinated coffee a day could reduce a person's heart failure risk.
Heart failure occurs when the organ is unable to pump blood around the body efficiently, usually because it has become too weak or stiff.
The serious condition tends to worsen over time, severely limiting a patient's activities and often becoming fatal.
Perhaps surprisingly, the study review suggests coffee must be caffeinated in order for a drinker to reap its heart-health benefits.
"The association between caffeine and heart failure risk reduction was surprising," said study author Dr David Kao.
"Coffee and caffeine are often considered by the general population to be 'bad' for the heart because people associate them with palpitations, high blood pressure, etc.
"The consistent relationship between increasing caffeine consumption and decreasing heart failure risk turns that assumption on its head.
"However, there is not yet enough clear evidence to recommend increasing coffee consumption to decrease risk of heart disease with the same strength and certainty as stopping smoking, losing weight or exercising."
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Heart-related disease is behind more than a quarter of deaths in the UK.
"While smoking, age and high blood pressure are among the most well-known heart disease risk factors, unidentified risk factors for heart disease remain," said Dr Kao.
Recent research has linked coffee to a reduced risk of type 2 diabetes and prostate cancer.
Nevertheless, an excessive consumption among pregnant women has been associated with altered brain pathways in a developing baby, which may affect their behaviour in later life.
Many also endure palpitations and insomnia if they overindulge.
"The risks and benefits of drinking coffee have been topics of ongoing scientific interest due to the popularity and frequency of consumption worldwide," said Dr Linda Van Horn from the American Heart Association's (AHA) nutrition committee.
"Studies reporting associations with outcomes remain relatively limited due to inconsistencies in diet assessment and analytical methodologies, as well as inherent problems with self-reported dietary intake."
To learn more, the Colorado scientists used machine learning to comb through the AHA's precision medicine platform, examining data from the Framingham Heart Study.
These data were referenced against the Atherosclerosis Risk in Communities and Cardiovascular Health studies.
The three studies had more than 21,000 participants between them, each followed for at least 10 years.
The overall results, published in the AHA's journal Circulation: Heart Failure, suggest people who drink one or more cups of caffeinated coffee a day have "an associated decreased long-term heart failure risk".
In the Framingham Heart and Cardiovascular Health studies specifically, the risk of heart failure went down by 5% to 12% "over the course of decades" per cup of coffee per day, compared with no consumption.
Zero to one cup of coffee a day was not linked to a reduced risk of heart failure in the Atherosclerosis Risk in Communities study.
The risk was instead reduced by around 30% among the participants who consumed at least two cups a day.
While many opt for decaffeinated coffee in a bid to be healthier, the studies threw up mixed results when it came to its heart benefits.
The Colorado scientists concluded, "caffeine consumption from any source appeared to be associated with decreased heart failure risk, and caffeine was at least part of the reason for the apparent benefit from drinking more coffee".
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For maximal health benefits, coffee should be drank without sugar. Milky-based drinks like lattes can also be high in calories, particularly if enjoyed with syrups.
"While unable to prove causality, it is intriguing these three studies suggest drinking coffee is associated with a decreased risk of heart failure and that coffee can be part of a healthy dietary pattern if consumed plain, without added sugar and high fat dairy products such as cream," said Dr Penny Kris-Etherton, immediate past chairperson of the AHA's lifestyle and cardiometabolic health council leadership committee.
"The bottom line: enjoy coffee in moderation as part of an overall heart-healthy dietary pattern that meets recommendations for fruits and vegetables, whole grains, low-fat/non-fat dairy products; and that also is low in sodium, saturated fat and added sugars.
"Also, it is important to be mindful caffeine is a stimulant and consuming too much may be problematic, causing jitteriness and sleep problems."
The Colorado scientists stressed the studies' participants self-reported their coffee consumption, which could have led to inaccuracies.
They also did not account for the type of coffee consumed, the origin of the beans, whether it was filtered or the size of the cup; all of which could affect caffeine intake.
The caffeine results also cannot be extrapolated to drinks like tea, soda or energy drinks; with only coffee being studied, added the scientists.