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Coffee, green tea, black tea and oolong tea consumption and risk of mortality from cardiovascular disease in Japanese men and women
  1. Yohei Mineharu1,2,
  2. Akio Koizumi1,
  3. Yasuhiko Wada3,
  4. Hiroyasu Iso4,
  5. Yoshiyuki Watanabe5,
  6. Chigusa Date6,
  7. Akio Yamamoto7,
  8. Shogo Kikuchi8,
  9. Yutaka Inaba9,
  10. Hideaki Toyoshima10,
  11. Takaaki Kondo10,
  12. Akiko Tamakoshi8,
  13. and the JACC study Group*
  1. 1Department of Health and Environmental Sciences, Kyoto University Graduate School of Medicine, Kyoto, Japan
  2. 2Department of Neurosurgery, Kyoto University Graduate School of Medicine, Kyoto, Japan
  3. 3Department of Medical Informatics, Kansai Rosai Hospital, Osaka, Japan
  4. 4Department of Social and Environmental Health, Osaka University Graduate School of Medicine, Osaka, Japan
  5. 5Department of Epidemiology for Community Health and Medicine, Kyoto Prefectural University of Medicine Graduate School of Medical Science, Kyoto, Japan
  6. 6Department of Food Science and Nutrition, Faculty of Human Life and Environment, Nara Women's University, Nara, Japan
  7. 7Infectious Disease Surveillance Center; Infectious Disease Research Division, Hyogo Prefectural Institute of Public Health and Environmental Sciences, Kobe, Japan
  8. 8Department of Public Health, Aichi Medical University, Aichi, Japan
  9. 9Department of Epidemiology and Environmental Health, Jissen Women's University, Tokyo, Japan
  10. 10Department of Public Health/Health Information Dynamics, Aichi Medical University, Aichi, Japan
  1. Correspondence to Professor Akio Koizumi, Department of Health and Environmental Sciences, Kyoto University Graduate School of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan; koizumi{at}pbh.med.kyoto-u.ac.jp

Abstract

Background The effects of coffee and green, black and oolong teas and caffeine intake on cardiovascular disease (CVD) mortality have not been well defined in Asian countries.

Methods To examine the relationship between the consumption of these beverages and risk of mortality from CVD, 76 979 individuals aged 40–79 years free of stroke, coronary heart disease (CHD) and cancer at entry were prospectively followed. The daily consumption of beverages was assessed by questionnaires.

Results 1362 deaths were documented from strokes and 650 deaths from CHD after 1 010 787 person-years of follow-up. Compared with non-drinkers of coffee, the multivariable HR and 95% CI for those drinking 1–6 cups/week, 1–2 cups/day and ≥3 cups/day were 0.78 (0.50 to 1.20), 0.67 (0.47 to 0.96) and 0.45 (0.17 to 0.87) for strokes among men (p=0.009 for trend). Compared with non-drinkers of green tea, the multivariable HR for those drinking 1–6 cups/week, 1–2 cups/day, 3–5 cups/day and ≥6 cups/day were 0.34 (0.06–1.75), 0.28 (0.07–1.11), 0.39 (0.18–0.85) and 0.42 (0.17–0.88) for CHD among women (p=0.038 for trend). As for oolong tea, the multivariable HR of those drinking 1–6 cups/week and ≥1 cups/day were 1.00 (0.65–1.55) and 0.39 (0.17–0.88) for total CVD among men (p=0.049 for trend). Risk reduction for total CVD across categories of caffeine intake was most prominently observed in the second highest quintile, with a 38% lower risk among men and 22% among women.

Conclusions Consumption of coffee, green tea and oolong tea and total caffeine intake was associated with a reduced risk of mortality from CVD.

  • Cardiovascular disease
  • coffee
  • heart disease
  • mortality
  • nutrition
  • stroke
  • teas
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Both coffee and tea are one of the most frequently consumed beverages worldwide. They are rich in caffeine and polyphenols, which have potent antioxidant properties and have been observed to play a protective role against cardiovascular disease (CVD).1 2 Although the relationship between coffee consumption and CVD has been extensively studied,3–7 few studies have examined the relationship between tea consumption and CVD.8–11 Instead, most studies have examined the association between coffee consumption and CVD and have focused on coronary heart disease (CHD) in which the association of coffee consumption with stroke remains unclear. In addition, most studies on the link between coffee consumption and CVD have been conducted in western countries, and only a few studies have been undertaken in Asian countries. The purpose of the present study was thus to examine comprehensively the relationship of the consumption of coffee, green, black and oolong tea with mortality from CVD among Japanese men and women in a large prospective cohort study with 1 010 787 person-years of follow-up. We also examined whether caffeine can be used to explain the effects of these beverages.

Methods

Study population

The Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC Study) started between 1988 and 1990. Details of our research methods have been published elsewhere.12 The study consisted of 110 792 individuals (46 465 men and 64 327 women) who were 40–79 years of age and living in 45 communities across Japan. Among them, data on the consumption of all beverages (coffee, green tea, black tea and oolong tea) were available for 36 332 men and 50 925 women. A total of 1977 men and 2615 women was then excluded from the study because of a history of stroke, CHD, or cancer at baseline. Therefore, 34 345 men and 48 310 women were involved in the present study. The ethical committees at Nagoya University and the University of Tsukuba approved the study.

Assessment of cardiovascular disease

For mortality surveillance in each community, investigators conducted a systematic review for death certificates, all of which were forwarded to the public health centre in the area of residency.13 Mortality data were sent centrally to the Ministry of Health and Welfare, and the underlying causes of death were coded according to the International Classification of Diseases, 9th revision, from 1988 to 1994 and the 10th revision from 1995 to 2003 for the National Vital Statistics. In Japan, registration of death is required by the Family Registration Law and is believed to be followed across Japan. Therefore, all deaths that occurred in the cohort were ascertained by death certificates from a public health centre, except for subjects who died after they had moved from their original community, in which case subjects were treated as censored cases. The follow-up was conducted until the end of 2003, and the average follow-up for the participants was 13.1 years. Cause-specific mortality was determined by total CVD (International Classification of Disease, 9th revision codes 390–459, 10th revision codes I01–I99), total CHD (codes 410–414 and I20–I25) and total stroke (430–438 and I60–I69), separately.

Assessment of consumption of coffee and caffeine intake

At baseline, consumption of coffee and teas was assessed using a self-administered dietary questionnaire as described previously.14 Briefly, participants were asked to state their average consumption of coffee, green, black and oolong teas during the previous year. They could select any of four frequency responses: ‘less than once a week’, ‘about one to two times a week’, ‘about three to four times a week’ and ‘almost every day’. Participants who selected the response of ‘almost every day’ were also asked to state their average consumption of these beverages in numbers of cups per day. The consumption of decaffeinated coffee or tea was not recorded because these products were not commercially available in Japan in the early 1990s. The estimated caffeine content was 153 mg per cup (170 ml) of coffee, 30 mg per cup (200 ml) of green tea, 51 mg per cup (170 ml) of black tea and 38 mg per cup (190 ml) of oolong tea. The mean caffeine intake was 287 mg/day for men and 254 mg/day for women. Relative proportions of caffeine intake by beverage were 45–49% from coffee, 47–48% from green tea, 1–2% from black tea and 3–6% from oolong tea.

The reproducibility and validity of this dietary questionnaire was reported previously.15 Briefly, the Spearman correlation coefficients between the two questionnaires, administered 1 year apart for 85 participants (eight men and 77 women), were 0.87 for coffee, 0.79 for green tea, 0.77 for black tea and 0.56 for oolong tea.15 The coefficients between the average of two questionnaires and four 3-day dietary records and four 1-week dietary records were 0.79 (8.0 cups and 7.1 cups per week) for coffee, 0.47 (25.4 cups and 30.1 cups per week) for green tea, 0.70 (1.4 cups and 1.6 cups per week) for black tea and 0.55 (1.8 cups and 1.2 cups per week) for oolong tea. When we restricted the data to the 77 women, the results were essentially the same.

Statistical analysis

We presented baseline characteristics according to the frequency of consumption of each beverage. Tests for trends were conducted using the median values of confounding variables in each category of beverage. The linear regression model was used for continuous variables and the logistic regression model was used for categorical variables.

The HR and 95% CI for CVD were calculated in each category of beverage and in each quartile of caffeine intake; less than one cup per week or the lowest quartile was used as the reference category. We estimated age and body mass index (BMI)-adjusted HR and multivariable HR using the Cox proportional hazards model, adjusting for age (in years), sex-specific quintiles of BMI (weight in kilograms divided by the square of height in meters), smoking status (never, former, or current (one to 19, 20–29, or ≥30 cigarettes/day)), alcohol intake (never, former, or current (one to 22, 23–45, 46–68, or ≥69 g/day)), hours of walking (<0.5, 0.5, 0.6–0.9 and ≥1.0 h/day), hours of participation in sports (<1, 1–2, 3–4 and ≥5 h/week), use of hormone therapy for women, history of hypertension (yes or no), history of diabetes mellitus (yes or no), perceived mental stress (low, medium and high), and educational level (primary school, junior high school, high school and college or higher). Furthermore, we adjusted for the consumption of other beverages, multivitamin use, vitamin E supplement use, consumption of total fruits, total vegetables, total bean products, total meats (continuous variable, servings/week for each food) and daily total energy intake (continuous variable, kcal/day). Sex-specific quintiles of BMI were used to account for different distributions between the sexes. We conducted a test for trend by treating median values of each category of beverage or caffeine intake as continuous variables. We also examined a possible non-linear relationship between mortality from total CVD and caffeine intake, coffee consumption or green tea consumption with cubic spline analysis using SAS macro.16 17 Four knots were set at quintiles 0.05, 0.35, 0.65 and 0.95.

We examined the association of each beverage consumption and total caffeine intake with the risk for CVD stratified by age group (40–59 years and 60–80 years), smoking status (non or ex-smokers and current smokers), alcohol intake (non or ex-drinkers and current drinkers), history of hypertension (yes and no), history of diabetes (yes and no), BMI (<25.1 kg/m2 and ≥25.1 kg/m2), educational level (before college and college or higher), total fruit intake (<3 servings/week and ≥3 servings/week), total vegetable intake (<3 servings/week and ≥3 servings/week) and total bean intake (<3 servings/week and ≥3 servings/week). The interactions with these stratified variables were tested by using cross-product terms of caffeine intake and the stratified variables. All analyses were conducted using the SAS statistical package, version 8.2. p Values for statistical tests were two-tailed, and 95% CI were estimated.

The authors had full access to the data and take responsibility for its integrity. All authors have read and agree to the manuscript as written.

Results

The baseline characteristics of the study cohort according to beverage consumptions are given in table 1 and table 2. During the 13.1-year follow-up of 34 345 men and 48 310 women aged 40–79 years (mean age of 57.1 years), we documented 1807 deaths from total CVD (404 total CHD and 782 total strokes) among men and 1557 (292 total CHD and 704 total strokes) among women. Age was associated with higher consumption of green tea and black tea and lower consumption of coffee and oolong tea for both men and women. BMI was positively associated with the consumption of oolong tea for men and women but were inversely associated with the consumption of coffee for men and women, green tea for men and black tea for women. A history of hypertension was inversely associated with the consumption of coffee and black tea, but it was not associated with the consumption of green tea and oolong tea. A history of diabetes was inversely associated with the consumption of coffee, green tea and black tea, but it was inversely associated with oolong tea consumption. Higher stress, higher vitamin E intake, higher multivitamin intake and less walking time were associated with a higher consumption of coffee, black tea and oolong tea and lower consumption of green tea. Achieving a higher educational level was associated with a higher consumption of coffee, black tea and oolong tea, but it was not associated with green tea consumption. In general, the consumption of vegetables, fruits and beans were positively associated with the consumption of teas but were inversely associated with coffee in both men and women. The association of current smoking and alcohol drinking with the consumption of the beverages varies among each beverage and among men and women.

Table 1

Baseline characteristics of men according to the consumption of coffee, green tea, black tea, and oolong tea: Japan Collaborative Cohort (JACC) Study, Japan, 1988

Table 2

Baseline characteristics of women according to the consumption of coffee, green tea, black tea, and oolong tea: Japan Collaborative Cohort (JACC) Study, Japan, 1988

A U-shaped association was found between coffee consumption and mortality from total CVD (table 3). In men, compared with those who drank less than one cup per week, the multivariable HR for total CVD among those drinking one to six cups a week, one to two cups a day and three or more cups a day were 0.71 (95% CI 0.53 to 0.96), 0.84 (95% CI 0.64 to 0.99) and 1.17 (95% CI 0.77 to 1.76). The corresponding data for women were 0.87 (95% CI 0.62 to 1.23), 0.77 (95% CI 0.55 to 0.99) and 2.30 (95% CI 1.31 to 4.02). The non-linear relationship was confirmed by cubic spline analysis (figure 1; non-linear p<0.001 for both men and women). On the other hand, coffee consumption was associated with linear risk reduction for mortality from stroke in men: the multivariable HR across categories of coffee consumption were 1.0, 0.78 (95% CI 0.50 to 1.20), 0.67 (95% CI 0.47 to 0.96), 0.45 (95% CI 0.17 to 0.87, p=0.009 for trend). The inverse association was more prominently observed among men, although interaction with sex was not statistically significant (p=0.204). We found no significant association of coffee consumption with CHD for either men or women.

Table 3

HR for mortality from CVD according to coffee consumption: JACC Study, Japan, 1988–2003 (n=82 655)

Figure 1

Multivariable HR for mortality from cardiovascular disease according to the consumption of coffee and green tea and caffeine intake, adjusted for body mass index (BMI), history of hypertension (HT), history of diabetes, smoking status, alcohol intake, education, walking hours, hours of sports participation, perceived mental stress, multivitamin use, vitamin E supplement use, consumption of total fruits, total vegetable, total beans, total meat, total fish and seaweeds and total daily energy intake in the JACC Study, Japan, 1988–2003 (n=82 655). *Indicates p<0.05. (A) Sex-specific HR curves and non-linear p values were drawn by cubic spline analyses with four knots at quintiles 0.05, 0.35, 0.65 and 0.95. Dots represent multivariable adjusted HR calculated by Cox proportional hazards model. (B) Sex-stratified HR was obtained in the stratified analysis by a history of hypertension and BMI.

We found that green tea consumption was associated with a lower risk of mortality from total CVD (table 4). In women, the multivariable HR of mortality due to total CVD based on green tea consumption compared with non-drinkers were 1.13 (95% CI 0.66 to 1.93) for one to six cups a week, 0.77 (95% CI 0.48 to 1.26) for one to two cups a day, 0.81 (95% CI 0.56 to 1.18) for three to five cups a day and 0.62 (95% CI 0.40 to 0.98) for six or more cups a day (p=0.031 for trend). The inverse association was not observed in men (p=0.047 for interaction). The corresponding data for CHD among women were 0.34 (95% CI 0.06 to 1.75), 0.33 (95% CI 0.07 to 1.11), 0.39 (95% CI 0.18 to 0.85) and 0.42 (95% CI 0.15 to 0.92, p=0.038 for trend).

Table 4

HR for mortality from CVD according to green tea consumption: JACC Study, Japan, 1988–2003 (n=82 655)

Black tea consumption showed no association with CHD, stroke or total CVD either among men and women (see supplementary table 1 (available online only), p=0.467 for interaction with sex). Oolong tea consumption of one or more cups per day was associated with a reduced risk of mortality from total CVD. Compared with those who drank less than one cup a week, the multivariable HR for total CVD among those drinking one to six cups a week and one or more cups per day were 1.00 (95% CI 0.65 to 1.55) and 0.39 (95% CI 0.17 to 0.88) in men (see supplementary table 2 (available online only), p=0.049 for trend). The inverse association was more strongly observed in men, although the interaction was not significant (p=0.261).

The relationship between caffeine intake and the risk of mortality from total CVD and stroke was U-shaped, in which the highest risk reduction was observed among persons with the second highest quintile (table 5). In men, the HR for mortality from total CVD across categories of caffeine intake were 1.0, 0.83 (95% CI 0.61 to 1.13), 0.70 (95% CI 0.50 to 0.98), 0.62 (95% CI 0.43 to 0.92) and 0.95 (95% CI 0.86 to 1.05; p=0.083 for trend). The inverse association was more pronounced in men than women (p=0.040 for interaction). A U-shaped association was also observed between caffeine intake and stroke. The multivariable HR for those with the second highest quintile for caffeine intake compared with those with the lowest quintile was 0.65 (95% CI 0.37 to 1.13) for men and 0.50 (95% CI 0.26 to 0.94) for women. The non-linear relationship was confirmed by cubic spline analyses (figure 1; non-linear p<0.001 for both men and women). No significant association was observed between caffeine intake and CHD.

Table 5

HR for mortality from CVD according to caffeine intake: JACC Study, Japan, 1988–2003 (n=82 655)

We conducted stratified analyses to evaluate whether the association between CVD and caffeine intake or the consumption of coffee or teas varied according to age, smoking status, alcohol intake, history of hypertension, history of diabetes, BMI, educational level, total fruit intake, total vegetable intake and total bean intake. Effect modification was observed for a history of hypertension and BMI in coffee consumption and caffeine intake (figure 1). The inverse association was more clearly observed for individuals with a history of hypertension (p=0.015 for coffee consumption and p=0.018 for caffeine intake) and non-obese individuals with a BMI less than 25 kg/m2 (p=0.003 for coffee consumption and p=0.006 for caffeine intake). No significant effect modification was observed for any variables in the consumption of teas.

Discussion

In the present large prospective study, we observed that the consumption of coffee, green tea and oolong tea and caffeine intake was associated with a lower risk of mortality from CVD for Japanese men and women. A U-shaped relationship was observed between the risk of mortality from total CVD and coffee consumption or caffeine intake. Moderate coffee consumption (one to two cups a day) was associated with a 16–23% lower risk of mortality from total CVD among men and women. The second highest quintile of caffeine intake was associated with a 22–38% lower risk of mortality from total CVD compared with a 4–5% lower risk in the highest quintile. In contrast to the U-shaped relationship between coffee consumption or caffeine intake and mortality from CVD, a higher amount of green tea consumption consistently decreased the risk of mortality from CVD. The inverse association was primarily observed among women, who had a 38% lower risk of mortality for those who drank six or more cups per day. Oolong tea consumption of one or more cups per day was associated with a 61% lower risk of mortality from total CVD among men. In contrast to the inverse association of green tea and oolong tea with mortality from CVD, black tea consumption did not show any association.

The U-shaped relationship between coffee consumption and CVD was consistent with recent epidemiological studies.3 5 6 18 Andersen et al5 reported in the Iowa Women's Health Study that moderate coffee consumption (one to three cups a day) was associated with the highest (29%) risk reduction of mortality from CVD. Similar observations were obtained in the Nurses' Health Study consisting of 83 076 women. In that study, participants who consume two to three cups a day of coffee had the lowest incidence of stroke. It should be noted that frequent coffee consumption (three or more cups per day) for women was associated with a 130% higher risk of mortality from total CVD compared with a 23% lower risk for moderate coffee consumption (one to two cups a day), showing a J-shaped relationship. In the CARDIO2000 case–control study consisting of 848 case subjects and 1078 control subjects,19 Panagiotakos et al19 reported a J-shaped association between coffee consumption and the risk of developing acute coronary syndrome. Compared with non-drinkers, those who consume more than four cups per day of coffee had a 3.24 times higher risk of developing acute coronary syndrome. In the present study, there were only a few individuals who drank four or more cups of coffee per day and, therefore, we could not examine the effect of excessive coffee intake among men. There thus remains the possibility that excessive coffee consumption might increase the risk of mortality from CVD in men as well as in women. In the stratified analysis, effect modification by history of hypertension was observed. Taking into account that a history of hypertension and smoking status showed opposite trends according to coffee consumption, one might suspect that a U or J-shaped relationship could be influenced by a history of hypertension and smoking status. However, a U or J-shaped relationship was also observed in non-smokers without a history of hypertension, indicating that smoking status and hypertension is unlikely to influence the non-linear relationship.

The inverse association between mortality from CVD and the consumption of green tea was consistent with previous studies.9 10 20–22 In the study by Kuriyama et al9 using 40 530 Japanese men and women, the inverse association was most pronounced for stroke but not for CHD, as shown in our study. The reason for the discrepancy between the studies is unclear. One possibility is a different classification of green tea consumption employed in each study (less than one cup a day, one to two cups a day, three to four cups a day, more than five cups a day in the study by Kuriyama et al;9 less than one cup a week, one to six cups a week, one to two cups a day, three to five cups a day and more than six cups a day in the present study). We thus employed the classification of green tea consumption used in the study by Kuriyama et al,9 but the results remained substantially the same after changing the classification (data not shown). Another possible explanation for the discrepancy is misclassification of the consumption of green tea. Because consumption of green tea was self-reported on the questionnaire in both studies, some misclassification of exposure was inevitable. Such misclassification might have yielded the null results in the relationship between mortality from stroke or CHD and green tea consumption.

The inverse association of oolong tea and CVD mortality was not previously noted. This may be partly because oolong tea was not so popular before the 1980s in Asian countries and it is not consumed worldwide. In contrast to the inverse association of green tea and oolong tea, black tea did not show any association with mortality from CVD, although an inverse association was shown in western populations.23 24 The null association of black tea with CVD mortality may be partly because black tea contains less antioxidant compounds such as caffeine or cathechin compared with other teas. Besides, most of the catechins in black tea are oxidised by fermentation to thearubigens and theaflavins, which have less antioxidant properties. Compared with the green tea that is not fermented, oolong tea (medium fermented) and black tea (fully fermented) have lower antioxidant properties (green tea>oolong tea>black tea).25 In our study population, only 1.5–2.0% consumed one or more cups of black tea. Therefore, the smaller amount of consumption might partly contribute to the lack of association.

The inverse association for the consumption of coffee and caffeine intake was more pronounced in stroke among men, whereas the inverse association for green tea consumption was more pronounced in CHD among women. Similar observations have previously been reported. Sesso et al26 showed the reduced risk of myocardial infarction by drinking tea (although black tea) but not by drinking coffee. Arts et al23 reported that tea consumption was associated with a reduced risk of CHD but not stroke. One possible explanation for the distinct properties between coffee and green tea might be that caffeine plays a major role in the inverse association between coffee and CVD mortality, whereas another compound in green tea such as catechin has more impact on CVD mortality than caffeine.

In the stratified analysis, an inverse association of caffeine intake or coffee consumption and mortality from CVD was predominantly observed among non-obese participants with a BMI less than 25 kg/m2 or among participants with a history of hypertension. There are two interesting reports that explain the relationship between BMI, hypertension, coffee and caffeine. It has been reported that the metabolic rate of caffeine is significantly lower (higher absorption, lower elimination and longer half-life) in obese individuals than lean ones.27 Interestingly, it has also been reported that coffee consumption was associated with an increased risk of hypertension for individuals with slow caffeine metabolism, whereas it was associated with a decreased risk of hypertension for individuals with faster caffeine metabolism.28 Taking into account that hypertension is an important risk factor for CVD, coffee consumption might increase the risk of CVD by inducing or worsening hypertension for obese individuals, whereas it will decrease the risk of CVD by improving hypertension for non-obese individuals. The BMI of women is significantly higher than that of men in our cohort, which might help to explain how the inverse association of coffee consumption or caffeine intake with fatal CVD is more clearly observed among men. In fact, the metabolic rate of caffeine was reported to be significantly slower in women than in men in several ethnicities.29 30 Coffee thus shows similar characteristics to those of caffeine (ie, an inverse association is prominently observed in stroke among men, non-obese individuals and individuals with a history of hypertension), indicating that caffeine intake mostly accounts for the inverse association of coffee with mortality from CVD. On the other hand, green tea shows distinct properties from coffee or caffeine, supporting the idea that the main compound in green tea that works against CVD is different from caffeine.

Tea catechins are a major candidate compound responsible for the inverse association of green tea with CHD among women, as tea catechins were previously shown to be associated with a reduced risk of CHD rather than stroke,23 and the antioxidant activities of catechins were proved to be higher in females than males in animal studies.31 32 Catechins have direct effects on cardiomyocytes,33 34 as well as vascular benefits that influence both CVD and cerebrovascular diseases. Direct cardioprotection by catechins might partly explain the more potent effects of green tea on CHD rather than stroke. A sex-specific association of green tea and CVD was also reported by Kuriyama et al,9 and they speculate that confounding by smoking might account for the sex specificity. However, in the present study, no effect modification by smoking habits was observed in the stratified analysis (p=0.396 for interaction). On the other hand, the consumption of green tea was associated with healthy behaviours, including increased physical activity or the increased consumption of fruits, vegetables and beans. Fruits, vegetables and beans are enriched with flavonoids or vitamins and have beneficial effects on CVD.35 36 Although we statistically controlled these variables and no effect modification by these healthy behaviours was observed, we could not exclude the possibility of residual confounding. Women consume a larger amount of healthy foods such as fruits, vegetables and beans than men, as was shown in the baseline characteristics of the present study. So, there remains the possibilities that healthy food intake might enhance the effect of catechins in green tea and might be associated with the sex difference of green tea benefits.

Compared with western populations, the metabolic rate of caffeine is much slower in Japanese individuals,37 38 which might have reduced the beneficial effects of caffeine. On the other hand, Japanese people consume fish, vegetables and beans rather than western-style food including red meat. Despite such genetic and environmental differences in risk profiles of CVD, a moderate consumption of coffee and teas was consistently associated with a reduced risk of CVD in both western and Japanese populations.

There are several limitations in the present study. First, we did not have data on other dietary sources of caffeine, such as soda, which is another potential source of caffeine. Soda consumption may confound the association between caffeine intake and the risk of CVD mortality. However, soda is consumed at a rate of approximately one tenth of coffee and teas in Japan, and it is consumed much less by middle-aged than younger people.39 Therefore, it is less likely that the consumption of soda negatively affected the results. Second, as the consumption of beverages was assessed on the basis of self-administered questionnaires, some misclassification of consumption status could arise. However, as we mentioned before, this misclassification may be non-differential and would tend to result in an underestimation of the impact of coffee, green tea and oolong tea consumption on CVD mortality. Finally, the observed inverse associations may be confounded by age because the consumption of coffee and oolong tea and caffeine intake was significantly inversely associated with age. To examine whether the association was confounded by age, we conducted both age-adjusted and age-stratified analyses. We could not observe any significant interaction with age. In addition, although green tea was positively associated with age, an inverse association was observed between green tea consumption and mortality from CVD. Therefore, it is less likely that the observed inverse associations between green tea and mortality were confounded by age.

In conclusion, the moderate consumption of coffee, green tea and oolong tea and caffeine intake was associated with a lower risk of mortality from CVD. Confirmation of the results of the present study by other non-western populations or randomised clinical trials will be worthwhile.

What is already known on this subject

  • Many studies have showed the inverse association between coffee consumption and CVD and have focused on CHD in which the association of coffee consumption with stroke remains unclear. Few studies have examined the relationship between tea consumption and CVD. These data are lacking in Asian countries.

What this study adds

  • This study showed a U-shaped relationship of coffee consumption and caffeine intake with the risk of mortality from CVD, especially stroke among Japanese men and women.

  • A higher amount of green tea consumption consistently decreased the risk of mortality from CVD, especially CHD among Japanese women.

Appendix

The present members of the JACC Study and their affiliations are as follows: Dr Akiko Tamakoshi (Nagoya University Graduate School of Medicine, present chairman of the study group), Dr Mitsuru Mori (Sapporo Medical University School of Medicine), Dr Yutaka Motohashi (Akita University School of Medicine), Dr Ichiro Tsuji (Tohoku University Graduate School of Medicine), Dr Yosikazu Nakamura (Jichi Medical School), Dr Hiroyasu Iso (Osaka University Graduate School of Medicine), Dr Haruo Mikami (Chiba Cancer Center), Dr Yutaka Inaba (Juntendo University School of Medicine), Dr Yoshiharu Hoshiyama (University of Human Arts and Sciences), Dr Hiroshi Suzuki (Niigata University School of Medicine), Dr Hiroyuki Shimizu (Gifu University School of Medicine), Dr Hideaki Toyoshima (Nagoya University Graduate School of Medicine), Dr Kenji Wakai (Aichi Cancer Center Research Institute), Dr Shinkan Tokudome (Nagoya City UniversityMedical School), Dr Shuji Hashimoto and Dr Yoshinori Ito (Fujita Health University School of Health Sciences), Dr Shogo Kikuchi (Aichi Medical University School of Medicine), Dr Akio Koizumi (Kyoto University Graduate School of Medicine), Dr Takashi Kawamura (Kyoto University Center for Student Health), Dr Yoshiyuki Watanabe and Dr Tsuneharu Miki (Kyoto Prefectural University of Medicine), Dr Chigusa Date (Faculty of Human Life and Environmental Sciences, Nara Women's University), Dr Kiyomi Sakata (Wakayama Medical University), Dr Takayuki Nose (Tottori University Faculty of Medicine), Dr Norihiko Hayakawa (Research Institute for Radiation Biology and Medicine, Hiroshima University), Dr Takesumi Yoshimura (Fukuoka Institute of Health and Environmental Sciences), Dr Akira Shibata and Dr Katsuhiro Fukuda (Kurume University School of Medicine), Dr Tomoyuki Kitagawa (Cancer Institute of the Japanese Foundation for Cancer Research), Dr Toshio Kuroki (Gifu University), Dr Yoshiyuki Ohno (Asahi Rosai Hospital), Dr Naoyuki Okamoto (Kanagawa Cancer Center), Dr Hideo Shio (Moriyama Municipal Hospital), Dr Kazuo Tajima (Aichi Cancer Center Research Institute), Dr Takashi Shimamoto (Osaka Medical Center for Health Science and Promotion) and Dr Heizo Tanaka (Medical Research Institute, Tokyo Medical and Dental University).

References

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Supplementary materials

Footnotes

  • * JACC Study Group members of the Japan Collaborative Cohort Study for Evaluation of Cancer Risk Sponsored by Monbusho (JACC Study) Group are listed in the appendix.

  • Funding Grants-in-Aid for Scientific Research from the Ministry of Education, Science, Sports and Culture of Japan (nos 61010076, 62010074, 63010074, 1010068, 2151065, 3151064, 4151063, 5151069, 6279102 and 11181101).

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval This study was conducted with the approval of the ethical committees at Nagoya University and the University of Tsukuba.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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