Stroke and heart attack survivors can reduce multiple causes of death and prevent further cardiovascular events by drinking green tea, according to new research published today in Stroke, a journal of the American Stroke Association, a division of the American Heart Association.
The study also found daily coffee consumption helps heart attack survivors by lowering their risk of death after a heart attack and can prevent heart attacks or strokes in healthy individuals.
Previous research has examined the benefits of green tea and coffee on heart health in people without a history of cardiovascular disease or cancer.
Researchers in the study “Green tea and coffee consumption and all-cause mortality among persons with and without stroke or myocardial infarction” sought to determine the effects of green tea and coffee consumption after surviving a stroke or heart attack.
“There is a strong need for scientific evidence on the lifestyles among survivors of stroke and heart attack considering the rapidly aging population and the need to improve life expectancy following these cardiovascular events,” says Hiroyasu Iso, M.D., a professor of public health at Osaka University in Suita, Japan, and the study’s corresponding author.
Researchers analyzed data of more than 46,000 participants (ages 40 to 79, 60% female) from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC study), a study conducted in 45 communities across Japan.
Participants were asked to complete self-administered questionnaires that included information about demographics, lifestyle, medical history and diet. People were then divided into three groups: history of stroke; history of myocardial infarction (MI); and no history of stroke or MI.
Researchers then analyzed the amount and frequency of green tea and coffee consumption. Researchers noted that a typical cup of green tea contains approximately 100mL (about 3.4 ounces) of liquid, and a typical cup of coffee contains approximately 150mL (about 5 ounces) of liquid.
When compared with participants who rarely drank green tea, stroke survivors who consumed at least seven cups of green tea daily lowered their risk of all-cause mortality by approximately 62%. Researchers did not observe a statistically significant association among participants without a history of stroke or heart attack.
Heart attack survivors who drank one cup of coffee a day reduced their overall risk of death by approximately 22% when compared to those who did not regularly drink coffee.
People without a history of stroke or heart attack who consumed one or more cups of coffee a week had approximately a 14% lower risk of all-cause mortality compared to non-coffee drinkers.
Green tea consumption can prevent further cardiovascular events in survivors, while drinking coffee can prevent such events in healthy individuals.
“An important distinction to make is that in Japanese culture, green tea is generally prepared with water and without sugar. Additionally, coffee is prepared with water and occasionally milk and sugar,” said Iso. “The healthiest way to prepare these beverages is without an unnecessary amount of added sugars.”
Researchers note that this study was observational, and the reason why drinking green tea and coffee lowered the risk of heart attack and stroke cannot be determined. Further research is needed to understand the details in the different effects of green tea and coffee.
Worldwide, the number of patients with diabetes is increasing in both developed and developing countries.1 Diabetic patients are at increased risk for classical micro- and macrovascular diseases as well as nonclassical diseases, such as dementia, malignancy, and fragility fracture, which affect both quality of life and life expectancy.2
Recent advances in therapeutics (such as sodium-glucose cotransporter 2 inhibitors, glucagon-like peptide-1 receptor agonists, and bariatric surgery) have been remarkable, however, lifestyle improvements are still regarded as the basic therapy.3 Lifestyle management comprises physical activity, smoking cessation, and nutrition therapy (including both food and beverages).3 However, epidemiological research on nonalcoholic beverages, such as green tea and coffee, has been scarce for diabetic patients.
Asian, especially East Asian, populations have a traditional habit of drinking green tea. Green tea derives from fresh leaves of Camellia sinensis, and it contains various chemicals, such as phenolic compounds, theanine, and caffeine.4
Through antioxidant, anti-inflammatory, or anti-bacterial properties,4 5 higher green tea consumption has been reported to confer health benefits, including preventing such chronic diseases as diabetes mellitus,4 6 and reduce mortality.7 8 Hitherto, however, no studies have investigated the association between green tea consumption and mortality in diabetic patients.
Coffee is one of the most frequently consumed beverages worldwide. It contains numerous bioactive chemicals, including phenolic compounds and caffeine, that have been reported to impact health through various mechanisms, such as antioxidant, anti-inflammatory, and anti-mutagenic effects:9 10 the result is a reduced risk of developing type 2 diabetes, dyslipidemia, or malignancy.10
In contrast to these health-promoting effects, coffee also has harmful effects, such as increasing blood pressure10 and the risk of myocardial infarction.11 In the general population, there is growing evidence that coffee consumption is associated with reduced risk of all-cause and cause-specific mortality.12–15
However, few epidemiological studies have examined this association in diabetic patients, and the results are controversial.16–19 This discrepancy may be due to the presence of diabetic complications, including cardiovascular disease (CVD), which could be affected by caffeine consumption.11
Further, most studies have been conducted only with developed country populations, which have higher risks of CVD than Asian ones.20
Recently, green tea has attracted considerable attention as a healthy beverage in developed countries.21 Japan has the culinary culture of both its own traditional food with green tea and developed country food with coffee: this provides a unique opportunity to investigate the combined effect of green tea and coffee consumption on mortality.
Accordingly, in the present study, we prospectively investigated the impact of green tea, coffee consumption, and their combination on all-cause and cause-specific mortality in Japanese patients with type 2 diabetes.
In this prospective study, we found that higher green tea and coffee consumption was significantly associated with decreased all-cause mortality in patients with type 2 diabetes. This association remained significant after adjusting for potential confounders: the impact of each beverage on mortality was independent. Similar trends were evident in analyzes of CVD-specific mortality. Further, the combination of higher green tea and coffee consumption significantly reduced all-cause mortality risk by 63%.
Hitherto, little research has investigated the association between green tea consumption and mortality in diabetic patients. Some epidemiological studies from Japan and China have reported the association between green tea consumption and mortality in the general population, including diabetic and non-diabetic individuals.
The Ohsaki Study was the first large-scale investigation on this subject: among 40 530 Japanese men and women, it found that those who consumed ≥5 cups/day of green tea had a 15% lower risk of all-cause mortality than those drinking <1 cup/day.6 A meta-analysis of five cohort studies of the general population (including diabetic and non-diabetic individuals) demonstrated that the HRs (95% CIs) of the highest vs the lowest green tea consumption were 0.80 (0.68–0.93) for all-cause mortality and 0.67 (0.46–0.96) for CVD mortality.7
The results of the present study are consistent with those of previous studies of the general population (including diabetic and non-diabetic individuals): however, we found the impact of green tea consumption to be even greater (HR for the highest vs lowest consumption, 0.60). To our knowledge, this is the first study to identify an association between higher green tea consumption and decreased all-cause mortality in type 2 diabetes patients.
The association between coffee consumption and mortality has been controversial in diabetic patients, although most studies have described beneficial effects in general populations (including diabetic and non-diabetic individuals). This association with diabetic patients was initially investigated with a Finnish diabetic population (3837 individuals) in 2006: a 30% significant reduction in all-cause mortality was observed in those who consumed ≥7 cups/day of coffee compared with those drinking 0–2 cups/day.16
However, the Health Professionals Follow-up Study of 3497 male diabetic patients found no association between coffee consumption and all-cause or CVD mortality.17 The National Health and Nutrition Examination Survey recently found that ≥200 mg/day of caffeine from coffee reduced all-cause mortality among 1974 women with diabetes, but not among men.19
Some large-scale studies of general populations have attempted to identify associations in subgroup analyses of diabetic patients. The National Institutes of Health-American Association of Retired Persons Diet and Health Study (total n=2 46 433) found that consuming ≥4 cups/day of coffee was associated with a 19% significant reduction of all-cause mortality in men and 14% insignificant reduction in women with self-reported diabetes.12
Similarly, in a US prospective cohort with 90 317 participants, drinking ≥4 cups/day of coffee was significantly associated with reduced all-cause mortality in diabetic patients.13 Conversely, in a Dutch population, the Alpha Omega Study involving 4837 patients with prior myocardial infarction determined that consuming more than four cups/day of coffee increased mortality by 24% in diabetic patients, whereas it decreased mortality by 27% in those without diabetes.14
In the Nurses’ Health Study (7170 female patients with diabetes), habitual coffee consumption was not found to be associated with increased risk of mortality.18 The UK Biobank (total n=498 134 participants) failed to identify a significant association between coffee consumption and mortality in diabetic patients.15
Most of the above studies were conducted in developed country populations, which have a higher risk of CVD than those in Asia.20 To our knowledge, the present investigation is the first prospective study to demonstrate a significant association between coffee consumption and reduced mortality in an Asian population with type 2 diabetes.
The mechanisms underlying reduced mortality with green tea and coffee consumption are not fully understood. Green tea contains a number of beneficial substances, including phenolic compounds, theanine, and caffeine.4 8 Epigallocatechin gallate is the most prevalent phenolic compound: it has been shown to have antioxidant, anti-inflammatory, and anti-mutagenic properties.27
Coffee also contains numerous bioactive components, including phenolic compounds and caffeine, which have been suggested as contributing to the associated favorable effects.9 Phenolic compounds, such as chlorogenic acid, have been reported to have a health impact through various mechanisms, such as antioxidant and anti-inflammatory actions.9 28
Caffeine is one of the components in green tea and coffee that could contribute to their favorable effects. The beneficial effects of caffeine on insulin sensitivity and glucose-induced insulin secretion have been suggested29 through several mechanisms, including weight loss and thermogenesis.30 31
However, previous studies have found that consumption of both caffeinated and decaffeinated coffee was associated with reduced mortality.12 That could mean that caffeine does not play a beneficial role in the association between coffee consumption and risk of mortality. Caffeine has also been reported to stimulate sympathetic activity and increase serum catecholamine levels,32 leading to increased blood pressure or CVD risk.11 33
The impact of coffee consumption on mortality was greater in the present study (HR 0.58) than that previously reported in developed country diabetic patients: HR 0.81 in men,12 HR 0.76,13 HR 0.70,16 and HR 0.53 in women.19 The difference may be explained by coffee having harmful effects among patients at higher CVD risk: that is based on findings that higher coffee consumption increased mortality among diabetic patients with previous myocardial infarction.14
Japanese type 2 diabetes patients are generally at lower CVD risk than developed ones:20 thus, caffeine may exert less detrimental effects on the vasculature, resulting in enhanced beneficial effects of coffee.
To date, no study has investigated the combined effect of green tea and coffee consumption on all-cause mortality. The present study determined that combined higher green tea and coffee consumption markedly reduced mortality. The Japan Public Health Center-Based Study found that the combination of ≥2 cups/day of green tea and ≥1 cup/day of coffee significantly reduced the risk for cerebral infarction and intracerebral hemorrhage.34
However, that effect did not apply to CHD: the study found no impact on CHD mortality. We found that the relative risk reduction of mortality (HR, 0.37) was greater than when consuming only green tea (HR, 0.72) or only coffee (HR, 0.76; figure 1, table 3), thus, the protective mechanisms of the two beverages may differ.
In addition to CVD and cancer, coffee reportedly confers health benefits with liver disease and dementia,10 however, reduced mortality associated with green tea is mostly explained with respect to CVD or cancer.7 8 Green tea and coffee consumption may be associated with different disease incidence or severity.
One strength of the present study is the high follow-up rate (99.5%), which enabled us to accurately investigate the association among green tea and coffee consumption and mortality. Further, this cohort study included potential confounders, such as sleep duration, diabetic complications, lifestyle, physical activity, laboratory data, and medications.
Some limitations of this study deserve mention. First, green tea and coffee consumption was assessed using single, self-reported data, which raises the problem of potential misclassification. However, the green tea and coffee consumption evaluated using our questionnaire showed high correlation with that found with 16 non-consecutive dietary records in a Japanese population.25
Second, we did not obtain information about some other confounding factors, such as educational and socioeconomic levels. Higher educational or income levels may be associated with greater coffee consumption:35 they may also be related to lower mortality risk.36
Those factors may be considered by adjusting for physical activities or smoking status, which could be associated with higher educational or income levels.36 However, a universal health insurance system has been established in Japan, thus, medical care is supposedly received regardless of educational or socioeconomic states. Third, the CVD medications differed among the coffee groups (table 1).
Those medications were not considered in the analyses, however, history of CVD was included as a confounding factor. Fourth, we did not assess whether coffee was caffeinated or decaffeinated. However, decaffeinated coffee is uncommon in Japan. Previous studies have found a similar association between caffeinated or decaffeinated coffee and mortality.12 13
Fifth, owing to the observational nature of the present study, we cannot conclude that consuming green tea or coffee reduces mortality. But long-term interventional studies of this kind may be difficult to implement: green tea and coffee are typically consumed as part of daily life. Sixth, the number of cause-specific deaths was relatively small.
That could lead to low statistical power in detecting significant associations. Seventh, there may have been multiple testing problems in our statistical analyses. Multiple testing corrections were not conducted in the present study, however, the results of table 2 are evidently consistent with those of previous studies.15 37 38
Finally, this study was conducted only among a Japanese population. The ingredients of Japanese green tea could differ from those in green tea in other countries.39 Accordingly, the findings of this study may not apply to other populations.
In conclusion, this prospective cohort study demonstrated that greater consumption of green tea and coffee was significantly associated with reduced all-cause mortality: the effects may be additive. Our results suggest that consuming green tea and coffee may have beneficial effects on the longevity of Japanese people with type 2 diabetes.
reference link: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7577036/
More information: Stroke (2021). DOI: 10.1161/STROKEAHA.120.032273
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