Chapter 18
Lifestyle+ — 9
Nonetheless, the overall good news on coffee and caffeine is complemented by studies looking at effects on the heart, particularly inducing rhythm disturbances like premature ventricular contractions (PVCs), premature atrial contractions (PACs), or atrial fibrillation. For decades patients have been warned against coffee for fear of just this kind of heightened risk to heartbeat. A randomized trial showed no increase in PACs but did show some increase in PVCs. Nearly 450,000 participants in the UK Biobank did not show a higher risk of arrhythmias among coffee drinkers. In fact, among another large study of UK Biobank participants, for every cup of coffee increase, there was a 3 percent lower risk of a heart rhythm disturbance, including atrial fibrillation and ventricular tachycardia. This study also looked at genetic markers that affect caffeine metabolism, such that slower metabolism might be linked with more arrhythmias—but that wasn’t the case.
The totality of the data support lack of hazard for coffee and caffeine, and the potential, albeit with some uncertainty, for some health benefits, even seen in some studies with decaffeinated coffee. If true, we don’t know how coffee promotes health. Many hypotheses have been offered, such as promoting brown adipose tissue, and one based on the insulin sensitivity of coffee’s polyphenol chlorogenic acid. Perhaps coffee works as an antioxidant, favorably modulates the gut microbiome, reduces inflammation, or facilitates DNA repair. This level of uncertainty about the causal connection is unsettling.
Alcohol
The profile we see in the evidence surrounding alcohol consumption is less blurry than for coffee and caffeine. Both moderate and heavy drinking does one no good. The long-standing myth about the benefits of red wine and the French connection was never adequately substantiated; instead, it’s been refuted in an analysis of almost six hundred thousand people in eighty-three prospective studies. The International Agency for Research on Cancer classifies alcoholic beverages as carcinogenic, with a strong link to oral cavity and esophageal cancers established in multiple cohort and case-control studies. Ireland is mandating labels on alcohol products: “There is a direct link between alcohol and fatal cancers.” Other countries, such as Canada, Norway, and Thailand, are beginning to follow suit. Most studies support a J-curve, with potential small benefit, both for cardiovascular and cancer, with light intake (such as two drinks per week), which varies by age, but significant risk beyond this level of consumption. A dose-response relationship between alcohol intake and high blood pressure has also been noted. This was reinforced by a UK Biobank study that also factored in genetic predisposition (known as Mendelian randomization) to alcohol consumption. The evidence supports a causal relationship between alcohol consumption and two different types of cardiovascular disease (fig. 3.3). One study showed a small added risk at less than seven drinks per week, but an exponential rise with higher intake levels. Perhaps the best summary from the mixed data is that light alcohol intake is not a problem, but the risks quickly increase.