Why the discrepancy? In many cases, earlier studies did not take into account other risk factors for heart disease, such as lack of exercise and smoking. These risk factors may be more common in dedicated coffee drinkers. More recent studies have taken care to control for these confounding risk factors. These more recent studies have suggested that, when consumed in moderation, coffee does not increase cardiac risk, and may often be beneficial.
Coffee and Blood PressureThe effect of coffee on blood pressure appears to be mixed. In non-coffee drinkers, acute exposure to caffeine can increase the blood pressure by up to 10 mm Hg. However, in chronic coffee drinkers, the acute ingestion of caffeine does not appear to raise the blood pressure. Several large studies have now failed to show a correlation between chronic coffee drinking and hypertension.
While these large population studies are reassuring, it appears likely that some individuals probably do have an increase in blood pressure when caffeine is ingested. So if you are diagnosed with hypertension, it still makes sense to try abstaining from coffee for a month or so, to see whether eliminating coffee benefits your blood pressure.
Coffee and ArrhythmiasThe belief that coffee causes cardiac arrhythmias is quite widespread, even among medical professionals. And indeed, it seems undeniable that some individuals will experience an increase in palpitations when they drink coffee.
However, neither large population studies nor studies in the laboratory have demonstrated that moderate amounts of coffee increase the risk of cardiac arrhythmias. Indeed, a recent study from Kaiser Permanente suggested that people who drank four cups of coffee per day had significantly fewer cardiac arrhythmias, including less atrial fibrillation and fewer PVCs.
At the very least, unless you are one of those individuals who notices a clear increase in palpitations after drinking coffee, there appears to be no reason to avoid moderate amounts of coffee because of a concern about cardiac arrhythmias.
Coffee and DiabetesSeveral studies have now shown a correlation between coffee consumption and a reduced risk of type 2 diabetes. At least one study showed that the same reduction in risk is seen with decaffeinated coffee, suggesting that the protective effect of coffee, with regard to diabetes, may not be due to its caffeine content.
Coffee and StrokeA large meta-analysis involving almost 500,000 participants failed to show any increase in the risk of stroke among coffee drinkers. In fact, in individuals who drank 1 to 3 cups of coffee per day, the risk of stroke was significantly reduced.
And in a more recent study from Japan, people who drank at least 1 cup of coffee per day (or 4 cups of green tea, which is a more common practice in Japan) had a 20% reduction in their risk of stroke over a 13-year period.
Coffee and Coronary Artery DiseaseSeveral large population studies have failed to show any increase in the risk of coronary artery disease among coffee drinkers. And in women, coffee drinking may even have a protective effect.
However, as is nearly always the case, in any large population there are many individuals who do not display "average" behavior. It turns out that there is a fairly common genetic mutation that causes individuals to metabolize caffeine slowly. It appears that in these individuals, the risk of coronary artery disease may be increased with coffee consumption. When genetic testing becomes more routine, it will be easy to identify these slow caffeine metabolizers.