Reveal the truth | Is drinking tea or coffee good for your heart?

Coffee and tea are among the most popular beverages in the world. A cup of fragrant coffee or tea after getting up in the morning can make you feel full of energy. The reason why coffee and tea can drive away sleepiness and restore energy is because they contain caffeine.

Caffeine is an adenosine receptor antagonist, and adenosine may affect cardiovascular function by affecting the release of neurotransmitters and catecholamines. Some researchers have found that drinking coffee and green tea is associated with a reduced risk of cardiovascular disease (CVD) after excluding other confounding factors such as lifestyle factors (such as smoking).

However, many people are still worried about whether caffeine intake will affect cardiovascular health, such as increasing blood pressure and arrhythmia. So is caffeine good or bad for cardiovascular health?

Recently, a study published in Nature Reviews Cardiology pointed out that moderate coffee drinking (2-5 cups a day) is associated with a reduced risk of cardiovascular disease. For most people, consuming 400 mg of caffeine per day is safe, and moderate coffee drinking can be part of a healthy lifestyle. The corresponding authors of the study are Professor Frank Hu and Professor Rob M. van Dam from the Harvard School of Public Health.

Screenshot source: Nature Reviews Cardiology

Whether physical discomfort occurs is related to the frequency of drinking

The study pointed out that in people who do not drink coffee regularly, caffeine intake can induce adrenaline release and increase blood pressure. However, if you drink coffee every day, you will develop tolerance to these effects of caffeine in just one week. Randomized trials have found that long-term caffeine intake only slightly increases blood pressure, which may be due to the interaction between other components in coffee and caffeine.

Similarly, coffee drinking may trigger myocardial infarction in people who don't drink coffee regularly, but it may not happen in people who drink coffee regularly. However, high levels of caffeine from energy drinks, especially after heavy drinking and exercise, are associated with cardiovascular events.

These findings justify the use of high doses of caffeine with caution, but for people who consume it regularly, there is less concern about its effects on CVD. In addition, habitual caffeine intake reduces appetite and increases energy expenditure, which may be beneficial for weight management.

In addition to caffeine, other ingredients are also worth paying attention to

It is worth noting that coffee and tea contain hundreds of other ingredients besides caffeine that may increase CVD risk. For example, studies have shown that drinking large amounts of unfiltered coffee (which contains more diterpenoid cafestol) may significantly increase serum cholesterol concentrations. However, the amount of cafestol in drip-filtered or instant coffee is negligible.

Another study found that cafestol, which is present in moderate amounts in espresso coffee, was associated with higher serum low-density lipoprotein cholesterol (LDL-C) levels. In contrast, flavonoids in green tea may lower serum cholesterol levels.

Furthermore, more than 20 cohort studies have shown that coffee drinking is associated with a reduced risk of type 2 diabetes. This association was similar for both decaffeinated and caffeinated coffee, highlighting that components other than caffeine, such as phenolic compounds, may improve glucose metabolism.

Therefore, cafestol in unfiltered coffee may increase serum cholesterol levels, but other components in coffee and tea may benefit cardiometabolic health.

Coffee drinking has little effect on cardiovascular health

The paper points out that although studies have found that moderate coffee drinking (2-5 cups per day; 1 cup is approximately equal to 250 ml) is associated with a reduced risk of coronary heart disease, stroke, heart failure and cardiovascular death, this association may be caused by other confounding factors.

For example, individuals with preclinical CVD may stop drinking coffee, resulting in a group of participants who may have a higher risk of CVD. Therefore, moderate coffee drinkers may have a lower risk of CVD compared with the control group because of the participants' better cardiovascular health at the beginning of the trial, not because of coffee drinking. In addition, studies have found that heavy coffee drinking is generally associated with unhealthy diet and lifestyle factors, so this may strengthen the relationship between coffee drinking and CVD risk.

Early studies have shown that caffeine intake may increase the risk of hypertension and myocardial infarction in individuals who metabolize caffeine slowly. About 95% of caffeine is metabolized by cytochrome P450 1A2 (CYP1A2), and we can be divided into fast or slow caffeine metabolizers based on whether we carry CYP1A2 gene variants.

However, more research data analysis later found that among people with different caffeine metabolism rates, caffeine intake was not significantly associated with the incidence of arrhythmias or other CVD in participants. Moreover, regardless of genetic characteristics, drinking up to 6 cups of coffee a day was not associated with a higher risk of arrhythmias or other CVD.

Several Mendelian randomization (MR) studies have analyzed genetic variants predicting the relationship between coffee intake and various cardiovascular outcomes, but none of them found any evidence for an inverse association between coffee intake and CVD risk.

Furthermore, MR analyses of coffee and caffeine intake have several limitations. First, statistical power is limited because genetic variants explain only a small portion of the variance in coffee intake. Second, MR analyses performed to date have generally assumed that coffee intake is linearly associated with CVD risk. Third, pleiotropic effects of genetic variants are likely to occur. For example, CYP1A2 metabolizes not only caffeine but also components of other foods and drugs. Finally, MR analyses of coffee intake do not take into account the biological mechanisms underlying coffee intake.

Image source: 123RF

In summary, short-term research evidence suggests that caffeine intake is associated with increased blood pressure, but we can develop tolerance to this effect. Although long-term epidemiological studies have found that moderate coffee drinking is inversely associated with CVD risk, MR analysis does not support a genetically determined association between caffeine or coffee intake and cardiovascular health. Neither traditional epidemiological studies nor MR studies have shown that moderate drinking of filtered coffee increases the risk of CVD, so moderate coffee drinking can be part of a healthy lifestyle.

These results are consistent with EU and US recommendations that caffeine intake of up to 400 mg per day is safe for most non-pregnant or non-lactating adults. Further research is needed to investigate the beneficial effects of other phytochemicals in tea and coffee, such as polyphenols.

References

[1] van Dam, RM, & Hu, FB (2022). Caffeine consumption and cardiovascular health. Nature Reviews Cardiology, 1-2.