By Ellen Feldman, MD
Altru Health System, Grand Forks, ND
Dr. Feldman reports no financial relationships relevant to this field of study.
SUMMARY POINTS
- These researchers investigated an association between coffee or tea consumption and coronary artery disease, progression, and events.
- Tea drinkers: Study participants who reported drinking ≥ 1 cup of tea each day had a statistically significant slower rate of coronary artery calcium progression and a lower rate of cardiac events, including myocardial infarction, cardiac arrest, and stroke.
- Coffee drinkers: Study participants who reported drinking < 1 cup of coffee each day had an increased rate of cardiovascular events; there was no association found between any level of coffee drinking and progression of coronary artery calcium.
- Caffeine intake was analyzed independently and appeared to have no association with cardiovascular events.
SYNOPSIS: A large, multi-ethnic study found that tea consumption was associated with slowed progression of coronary artery disease and lowered risk of cardiovascular events when compared to never drinkers; coffee intake appears to have no measurable effect.
SOURCE: Miller PE, Zhao D, Frazier-Wood AC, et al. Associations of coffee, tea, and caffeine intake with coronary artery calcification and cardiovascular events. Am J Med 2017;130:188-197.
Tea or coffee? Both are among the most widely consumed beverages across the world.1 Often, the choice is simple and based on preference and habit, but increasingly patients are asking which of these beverages is better for them and for health. Popular beliefs seem to sway toward tea as the more beneficial drink; however, definitive studies in this area still are pending.
We know that coffee consumption is related to a lower incidence of diabetes and improved endothelial function.2 In June 2016, the World Health Organization declassified coffee as a carcinogen and noted it has protective effects against specific carcinomas (liver and uterus).3 However, studies of the effect of coffee on cardiovascular health have been less definitive and limited by homogeneity among the study group and perhaps confounded by the association of tobacco use with coffee consumption.
For centuries, tea — a beverage brewed from the leaves of the Camellia sinensis plant — was known throughout the Eastern Hemisphere for its widespread medicinal uses. As interest in possible health benefits of this plant spread to the western world in the 1980s, research into the properties and mechanism of action accelerated.4 Most researchers believe the benefits of tea derive from the abundant flavonoids in all forms of tea, although some forms have more antioxidants than others. Flavonoids, known to have antioxidant and anti-inflammatory properties, are found in most fruits and vegetables. Current studies suggest potential health benefits in many disorders, including specific carcinomas, hypertension, and disorders of the eye, such as glaucoma and retinopathy, but studies have had conflicting results, particularly when field-tested on humans.4,5
Noting that confounding variables, such as ethnic background, socioeconomic status, and nutritional intake, contaminate many studies looking at tea, coffee, and cardiovascular disease, Miller et al studied a diverse population and controlled for these factors. The Multi-Ethnic Study of Atherosclerosis (MESA) is a prospective, multicenter study looking at the prevalence, risk factors, and progression of subclinical cardiac disease.6 The entire population-based group of 6,814 men and women (ages 44-84 years) enrolled in MESA were screened for eligibility in this study. Included for analysis in the Miller et al study were all MESA participants without baseline cardiovascular disease who completed the portion of the questionnaire regarding coffee and tea intake; 6,508 participants met these criteria for eligibility. More than 90% completed the interviews, beginning with a detailed questionnaire in 2000-2002, and continuing with yearly telephone calls and hospital record review until 2013.
Coffee and tea consumption were self-reported on the initial food-frequency questionnaire. Gradations of frequency ranged from never consumed to more than six cups daily. There was no distinction between caffeinated or decaffeinated coffee or tea, nor any distinction regarding black or green tea. No questions were asked regarding herbal or other commonly labeled “tea” products. Caffeine consumption was calculated separately from all available sources (food and beverage.)
Coronary artery calcium (CAC), a measure of subclinical atherosclerosis, was scored at baseline and progression or score changes were noted at follow-ups.
To eliminate confounding factors and isolate an association between tea or coffee and cardiovascular disease, the authors used four different models for analysis. Each model was progressively more comprehensive, ranging from Model 1, adjusting for age, sex, and ethnicity, to Model 4, adjusting for multiple factors, including lifestyle factors, medications, family history, and C-reactive protein and fibrinogen. A baseline ethnicity analysis showed higher tea intake among the Chinese American participants in the study. Given the lower incidence of cardiovascular events among this group, a sensitivity analysis was performed excluding this subgroup. This did not significantly affect the final results or study conclusions. See Table 1 for selected results from the study.
Table 1: Selected Results for Coffee vs. Tea Drinkers |
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Results were considered significant if P values (2-sided) were < 0.05. In this chart, significant results are bolded. All results are for Model 4, which includes the most comprehensive adjustment for confounding factors. |
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Results for Coffee Drinkers |
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|
Never drink |
< 1 cup daily |
> 1 cup daily |
|
|
CAC prevalence 1-99 at baseline |
1 |
1.07 (0.88-1.30) |
1.02 (0.85-1.21) |
|
CAC prevalence ≥ 100 at baseline |
1 |
1.18 (0.93-1.49) |
1.10 (0.89-1.15) |
|
CAC progression ratio |
1 |
1.11 (0.95-1.29) |
1.06 (0.92-1.22) |
|
Hazard ratio (95% confidence interval) between coffee and cardiovascular event |
1 |
1.28 (1.02-1.61) |
0.97 (0.78-1.20) |
|
Results for Tea Drinkers |
|||
|
Never drink |
< 1 cup daily |
> 1 cup daily |
|
|
CAC prevalence 1-99 at baseline |
1 |
0.96 (0.81-1.12) |
0.90 (0.73-1.12) |
|
CAC prevalence ≥ 100 at baseline |
1 |
1.03 (0.86-1.24) |
0.64 (0.49-0.84) |
|
CAC progression ratio |
1 |
0.96 (0.85-1.09) |
0.73 (0.61-0.87) |
|
Hazard ratio (95% confidence interval) between coffee and cardiovascular event |
1 |
0.92 (0.76-1.10) |
0.71 (0.83-0.95) |
|
Results for Caffeine Consumption |
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|
Lowest tertile |
Second tertile |
Third tertile |
|
|
CAC prevalence 1-99 at baseline |
1 |
0.99 (0.84-1.18) |
0.89 (0.74-1.07) |
|
CAC prevalence ≥ 100 at baseline |
1 |
0.81 (0.66-1.00) |
0.82 (0.66-1.01) |
|
CAC progression ratio |
1 |
0.87 (0.76-1.00) |
0.88 (0.76-1.02) |
|
Hazard ratio (95% confidence interval) between coffee and cardiovascular event |
1 |
0.96 (0.79-1.17) |
0.87 (0.70-1.07) |
COMMENTARY
Does this comprehensive, meticulously designed, multi-ethnic, and multisite study with participants selected to represent a population-based sample definitively answer the question of which beverage (tea or coffee) conveys greater benefits for cardiovascular health? Not definitively, but the results of this study suggest that regular tea consumption is associated with decreased prevalence of CAC, slowed progression of CAC, and a decreased incidence of cardiovascular events. However, there is no indication from this study that consumption of coffee or of caffeine (found in both beverages) is harmful or a factor in progression of CAC, and there is no association between caffeine use and incidence of cardiac events.
One question arising from the results of this study may be related to the coffee findings; that is, does a low consumption of coffee lead to an increased risk of a cardiovascular event? It is important to note that there was no association with increased accumulation of CAC among those reporting any frequency of coffee use, but an increase in actual cardiovascular events was noted among low frequency users. One explanation for this finding may be that some participants with known higher risk of cardiac problems chose to avoid coffee or were advised to do so. However, without more data the causality is unclear, and this remains an area for further investigation and research
The strengths of this study are considerable and include consistent results across a diverse population and multi-step efforts to eliminate confounding variables. The results of this study did not seem to differ among various ethnic groups and, in fact, remained valid even with exclusion of data from Chinese Americans (a group with a high consumption of tea and lower cardiovascular disease risk.) Likewise, the longitudinal nature of the study and the investigation of multiple related cardiovascular factors — including the prevalence of CAC, the progression of CAC, and the occurrence of cardiovascular events — are unique aspects that enhance the study value.
However, the prospective nature of this investigation does not allow room for changes in habit or of beverage consumption over time; the recording of beverage consumption was dependent solely on recall at the time of the baseline questionnaire. Thus, these results are best interpreted with the understanding that there is no information available regarding ongoing consumption of tea or coffee over the study period. Future studies designed to eliminate the need for recall and looking at ongoing use of these beverages will be helpful in contributing more to this field.
The observational nature of this study makes it difficult to move from association to causation. Future efforts should move toward more active, interventional studies. In doing so, understanding the effect from a specific type of tea (black, green, oolong — all with differing antioxidant content) also will help advance the field and allow better clinical recommendations. Designing a study to try to isolate the effect of tea (as opposed to the overall effect of a healthy lifestyle inclusive of tea) will help clarify this question of causation as well.
Finally, it is useful to consider that “tea” in a strict sense is a beverage derived from the leaf of the Camellia sinensis plant. The various types of tea all come from the leaves of this plant but differ in the process of drying and fermentation.7 However, in many U.S. stores today, there are preparations promoted and advertised as “tea” that technically do not belong to this category. It may be that the original MESA questionnaire attempted to eliminate these “non-teas” by asking for green or black tea consumption, but the possibility of confusion due to widespread use of the term “tea” may have influenced consumption reporting.
Sometimes, it seems as if the world is divided between two types of people: tea drinkers and coffee drinkers. A more nuanced view is that a definitive choice is neither necessary nor medically recommended; a healthy diet can include both beverages and, if desired, a person can tailor use to preference and specific health issues. Although a simple concept, this approach can be broadened — searching for inclusion rather than exclusion and enjoying diversity in diet are two important principles to consider when talking with patients about the important role of nutrition in health.
Clinically, the results of this study affirm that providers, backed by evidence that regular tea use is associated with a reduction in CAC and cardiac events, stand on firm ground recommending tea as an important component of a diet focused on cardiac health. Acknowledging that coffee consumption appears safe from a cardiac viewpoint, but not necessarily protective, is an equally valid message. It is worth noting that this study did not attempt a head-to-head (or cup-to cup) comparison and that both beverages can contribute meaningfully to a multi-flavored, healthy lifestyle.
REFERENCES
- Pew Research Center. Desilver D. Chart of the Week: Coffee and the around the world. Available at: http://www.pewresearch.org/fact-tank/2013/12/20/chart-of-the-week-coffee-and-tea-around-the-world/. Accessed May 1, 2017.
- Huxley R, Lee CM, Barzi F, et al. Coffee, decaffeinated coffee, and tea consumption in relation to incident type 2 diabetes mellitus: A systematic review with meta-analysis. Arch Intern Med 2009;169:2053-2063.
- World Health Organization. International Agency for Research on Cancer. IARC monographs evaluate drinking coffee, mate, and very hot beverages. Available at: https://www.iarc.fr/en/media-centre/pr/2016/pdfs/pr244_E.pdf. Accessed May 1, 2017.
- Khan N, Mukhtar H. Tea and health: Studies in humans. Curr Pharm Des 2013;19:6141-6147.
- Qiao J, Kong X, Kong A, Han M. Pharmacokinetics and biotransformation of tea polyphenols. Curr Drug Metab 2014;15:30-36.
- MESA. Available at: https://mesa-nhlbi.org. Accessed May 1, 2017.
- Tenore GC, Daglia M, Ciampaglia R, Novellino E. Exploring the nutraceutical potential of polyphenols from black, green and white tea infusions - an overview. Curr Pharm Biotechnol 2015;16:265-271.
A large, multi-ethnic study found that tea consumption was associated with slowed progression of coronary artery disease and lowered risk of cardiovascular events when compared to never drinkers; coffee intake appears to have no measurable effect.
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