The previously-mentioned epidemiological studies on coffee/caffeine consumption and various heart effects were conducted with healthy participants. Additionally, there have been an increasing number of studies that start with patients having a specific disease, such as diabetes, myocardial infarction, or hypertension34,62,63. Effects in diseased people can be different from effects in healthy people. These observations deserve further exploration, and may explain some of the variation in results mentioned above in the epidemiological studies.
- In the Health Professionals Follow-up Study, results from 3,497 diabetic men indicated that regular coffee consumption is not associated with increased risk of cardiovascular disease or mortality62.
- In a Swedish cohort, coffee consumption and mortality after a first acute myocardial infarction was evaluated (1,369 participants and 289 subsequent cases). Coffee consumption at the time of hospitalisation for the first myocardial infarction was inversely associated with subsequent post-infarction mortality63.
- In a small Italian prospective cohort, 553 stage-1 hypertensives were followed up for 8 years, with 323 developing hypertension. Patients with genetic differences, in particular different P450-1A2 genotypes, showed a different risk of hypertension associated with coffee consumption. The slow metabolizers (carriers of the slow *1F allele) showed a risk associated with coffee, whereas this was not the case in the fast metabolizers64.
- A 2016 study of 715 hypertensive participants suggested that those consuming ≥3 cups of coffee per day showed higher 24-hour systolic blood pressure (BP) than non-coffee drinkers. The association was similar among individuals who were smokers, had excess weight, low adherence to the Mediterranean diet, or hypercholesterolemia. In conclusion, habitual coffee consumption was associated with uncontrolled BP in a hypertensive older population65.
- A study evaluated the association between long-term coffee consumption and 10-year cardiovascular disease incidence among Acute Coronary Syndrome (ACS) patients, suggesting that 1-2 cups of coffee per day versus no consumption had an adverse effect on the ACS incidence. The authors concluded that avoidance of coffee may be beneficial in those with Acute Coronary Syndrome66.
- A dose response meta-analysis in patients who had suffered acute myocardial infarction concluded that drinking coffee habitually following AMI was associated with a reduced risk of mortality67.
- A review of studies on patients with high blood pressure, cardiovascular disease, or cardiac arrhythmias, concluded that coffee consumption in moderation (3-4 cups/day), is safe and potentially beneficial in these patients68.
In addition, there are also a number of trials and cross-sectional studies of coffee and caffeine intake:
- A small Greek cross-sectional study within a group of 374 patients, who had suffered an acute coronary syndrome, compared the subgroups who did and did not develop left ventricular systolic dysfunction. They observed that in normotensive patients, coffee consumption at all levels was associated with a substantially lower risk of developing left ventricular systolic dysfunction, whereas in hypertensive patients, the risk increased in the group consuming 3 or more cups per day69. It is, however, not clear whether the association in hypertensives reached statistical significance.
- A UK randomised trial tested heart rate variability in myocardial infarction patients after they consumed either caffeinated or decaffeinated coffee for 5 days. Coffee consumption was not associated with an adverse cardiovascular outcome in the short term70.
- A small Swiss trial (15 patients with coronary heart disease and 15 age-matched controls) tested for myocardial blood flow response during physical exercise before and after 200mg of oral caffeine. They observed reduced myocardial blood flow in the caffeine/exercise groups, the strongest in the patient group. No change was seen for both groups in the caffeine/resting situation71.
- A small trial comparing patients with and without coronary artery disease concluded that acute caffeine ingestion significantly improved endothelial function in both groups and was associated with lower plasma markers of inflammation72.
Results of patient studies should be interpreted with caution. Because of the inherent difficulty in recruiting diseased participants, these studies tend to have relatively small numbers of participants. Also, the (ongoing) treatment of the patient can interfere with the study/trial. Therefore, results in patients and in healthy people can differ.
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