Association of Green Tea Consumption and Coronary Arterial Disease Risk in a Chinese Population in Guangzhou

Abstract

Objective:

To explore the association between green tea consumption and coronary arterial disease (CAD) in the Chinese population of Guangzhou.

Design, location, subjects:

A retrospective study at the Sun Yat-sen Memorial Hospital in Guangzhou, China. Consecutive patients were enrolled between January 2013 and August 2014. A total of 539 patients were included. Two hundred sixty-seven of them are CAD patients and 272 of them are non-CAD patients. The CAD patients were diagnosed according to international diagnostic criteria.

Interventions:

Using data from the questionnaires and clinical laboratories, we attempted to elucidate the association between green tea and CAD.

Outcome measures:

Baseline characteristics of study population, CAD-related biomarkers, amount, frequency and duration of green tea consumption, and CAD risk analysis.

Results:

The results showed that among males, those who drank green tea did not have a reduced risk of CAD (odds ratio; OR = 1.58, 95% CI: 0.96–2.59, p > 0.05). However, women in the study who drank green tea had a reduced risk of CAD (OR = 0.13, 95% CI: 0.07–0.23, p < 0.01). The females who consumed ≤1 cup/day green tea had lower CAD risk (OR = 0.12, 95% CI: 0.07–0.23, p < 0.01). The frequency of 3–5 days/week (OR = 0.14, 95% CI: 0.07–0.29, p < 0.01) and >5 days/week (OR = 0.24, 95% CI: 0.08–0.69, p < 0.01) were both beneficial in preventing CAD. Those who had been drinking green tea for 0–10 years (OR = 0.11, 95% CI: 0.04–0.30), 10–20 years (OR = 0.22, 95% CI: 0.11–0.46), or >20 years (OR = 0.37, 95% CI: 0.12–0.96) had a reduced risk of CAD.

Conclusions:

Through the analysis of green tea consumption and CAD-related biomarkers, we concluded that a small amount of high-frequency green tea consumption was associated with a reduced risk of CAD in female populations in Guangzhou, China, and the association might be partly due to altered CAD-related biomarkers.

Introduction

Coronary arterial disease (CAD) has become the leading cause of death worldwide.¹ One out of every five adults in China suffers from CAD.² The risk factors include aging, imbalanced diets, unhealthy behaviors, and the raising standard of living.³ More attention should be paid to this disease and more effective methods need to be developed, to reduce its incidence.

Tea is one of the world's three major beverages,⁴ including black, green, and yellow teas.⁵ Green tea is derived from the leaves of Camellia sinensis, and is especially popular in Asia.⁶ Green tea contains ingredients that have been shown to be beneficial to health,⁷ such as carotene, thiamine, riboflavin, nicotinic acid, and ascorbic acid, as well as minerals, including calcium, magnesium, iron, sodium, zinc, copper, phosphorus, and selenium.⁸ In addition, other ingredients, such as caffeine and polyphenols, may help regulate dyslipidemia.⁹

Now several studies have reported that the green tea could reduce the incidence of coronary heart diseases.^10,11 Ohmori et al. reported that green tea consumption was found to be inversely associated with myocardial infarction in Japanese patients. Wang et al. carried out a study with 520 consecutive patients who underwent coronary arteriography, and the results showed that green tea consumption could protect against the development of coronary atherosclerosis in Chinese male patients.¹² In Sano's study with 203 patients who underwent coronary angiography, the results showed that green tea consumption was associated with a lower incidence of CAD in the population in Japan.¹³ Because of the high consumption of green tea in China and relatively high rate of CAD incidence and mortality, exploring the health effects of green tea on CAD might provide clues to resolve an important public health issue. Therefore, we aimed to verify the relationship between green tea and CAD incidence, and attempted to elucidate the association between green tea and CAD-related biomarkers.

Materials and Methods

Study population

We originally enrolled a total of 759 consecutive patients between January 2013 and August 2014 in the Second Hospital of Sun Yat-sen University. Ten patients failed to complete the basic information. We excluded 80 patients with arrhythmias and cardiomyopathy and 130 who drank other types of tea (black tea or oolong tea). Finally, a total of 539 patients were included. Two hundred sixty-seven of them are from the CAD patients and 272 of them are non-CAD. Baseline measures of cardiac function, liver function, blood lipid, and blood coagulation function indices were recorded. Information about green tea consumption was also collected. The CAD patients were diagnosed according to international diagnostic criteria. The Ethics Committees at Sun Yat-sen Memorial Hospital approved the study. CAD patients were diagnosed by (1) acute chest pain; (2) the ischemic change image in exercise electrocardiography; (3) ≥50% lumen diameter reduction in at least one major coronary artery in coronary angiography. The non-CAD group was selected from the people who were excluded from the diagnosis of CAD after the specialized examination in the hospital.

Data collection

Trained interviewers used a structured questionnaire to collect baseline information, including height, weight, and age. Body–mass index (BMI) was calculated as weight (kg) divided by height (m), squared. Cardiac function, liver function, blood lipid, and blood coagulation function indices were recorded, which included left ventricular ejection fraction (LVEF), left atrial diameter (LAD), left ventricular end diastolic diameter (LVEDD), creatine kinase (CK), CK mb, triglycerides (TC), triglyceride (TG), high-density lipoprotein (HDL), low-density lipoprotein (LDL), prothrombin time (PT), fibrinogen (FBG), activated partial thromboplastin time (ATPP), thrombin (TT), lymphocyte, monocyte (MONO), and platelet aggregation (PAG). Blood samples from all of the patients were taken before breakfast and tested by clinical laboratory. Trained staff collected the information from the questionnaires.

We also designed a basic questionnaire to collect information on green tea consumption. Beverage consumption was assessed by asking: “Did you usually consume beverages, including plain water, black tea, oolong tea, green tea, coffee, cola and juice during the last year?” and participants were asked to select one or two most often consumed beverages. Green tea consumers were defined as a participant who selected green tea as one of the most often consumed beverages. For the green tea consumers, the quantity (none, ≤1, or >1 cup/day), frequency (none, 1–2, 3–5, or >5 days/week), or duration (none, 0–10, 10–20, or >20 years) of green tea consumption were inquired.

Statistical analysis

Continuous variables were presented as mean ± standard deviation and variance was used for analysis. Discrete variables were presented as proportions of the total number (percentages) and Chi-square test was used. Univariate and multivariate logistic regression models were used to calculate the prevalence of CAD. Analysis of covariance was performed to adjust for the effect. SAS 9.3 (SAS institute, Inc., Cary, NC) was used to analyze all of the data. p < 0.05 was considered statistically significant.

Results

Baseline characteristics of study population

As shown in Table 1, a total of 539 patients were enrolled, including 280 males and 259 females. Around 61.8% (173/280) males were CAD patients. In this study, women in the study who drank green tea had a reduced risk of CAD; however, men who drank green tea did not have a reduced risk of CAD. The percentage of men who drink tea is 66.4% (186/280), whereas women who drink tea is 35.9%(93/259). It is reported that more men drink tea compared with women. For the male patients, the BMI values of CAD patients (23.9 ± 2.7) were higher than non-CAD males (21.3 ± 2.1). The LVEF (63.1% ± 12.1%) values of the CAD group were lower than those of the non-CAD group (66.4% ± 9.3%). The CAD group also had lower scores of blood coagulation biomarkers PT (10.7 ± 0.8), ATPP (26.4 ± 2.7), and higher scores of FBG (3.0 ± 0.4) than those of the non-CAD group, (PT [11.4 ± 0.9], ATPP [27.4 ± 3.6] and FBG [2.6 ± 0.6]) (p < 0.01). Among the female participants, those with CAD had higher BMI (23.4 ± 3.3) than the non-CAD participants (22.3 ± 3.1). The systolic blood pressure of CAD patients (132.0 ± 14.7) were higher than the non-CAD participants (127.8 ± 18.0). The CAD group had worse cardiac function compared with the non-CAD group (LVEF: [64.6 ± 10.8] vs. [69.3 ± 5.2], LAD: [34.3 ± 4.5] vs. [32.4 ± 4.0], LVEDD: [47.3 ± 4.1] vs. [46.0 ± 3.3]). The blood lipid indices of the CAD group were worse than that of the non-CAD group (TC: [5.3 ± 1.2] vs. [4.7 ± 1.0], TG: [2.0 ± 1.1] vs. [1.5 ± 1.1], LDL: [3.0 ± 0.8] vs. [2.7 ± 0.8]) (Table 1). The basic characteristics of patients in different groups were adjusted. The differences of CAD-related biomarkers were consistent with other studies.

Table 1.

Characteristics of Patients With and Without Coronary Arterial Disease

	Male			Female
	CAD (n = 173)	Non-CAD (n = 107)	p	CAD (n = 94)	Non-CAD (n = 165)	p
Height	167 ± 4.2	168.0 ± 4.5	0.06	160.0 ± 5.2	159.0 ± 4.1	0.11
BMI	23.9 ± 2.7	21.3 ± 2.1	0.04^a	23.4 ± 3.3	22.3 ± 3.1	<0.01^a
Age	62.5 ± 10.7	55.0 ± 12.0	<0.01^a	67.5 ± 9.7	57.0 ± 11.0	<0.01^a
SBP	127.0 ± 18.8	129.0 ± 16.4	0.35	132.0 ± 14.7	127.8 ± 18.0	0.04^a
DBP	74.9 ± 10.4	77.2 ± 9.1	0.05	75.7 ± 10.4	76.0 ± 11.5	0.83
LVEF	63.1 ± 12.1	66.4 ± 9.3	0.01^a	64.6 ± 10.8	69.3 ± 5.2	<0.01^a
LAD	34.1 ± 4.5	34.4 ± 5.2	0.62	34.3 ± 4.5	32.4 ± 4.0	<0.01^a
LVEDD	49.3 ± 5.8	49.0 ± 5.9	0.68	47.3 ± 4.1	46.0 ± 3.3	<0.01^a
CK	98.0 ± 56.9	104.4 ± 54.1	0.35	93.4 ± 55.0	94.2 ± 77.6	0.92
CKMB	12.6 ± 5.3	12.5 ± 5.0	0.87	13.8 ± 4.4	12.6 ± 4.9	<0.01^a
TC	4.7 ± 1.3	4.6 ± 1.0	0.47	5.3 ± 1.2	4.7 ± 1.0	<0.01^a
TG	1.8 ± 0.90	1.6 ± 0.9	0.07	2.0 ± 1.1	1.5 ± 1.1	<0.01^a
HDL	1.1 ± 0.3	1.1 ± 0.3	1.0	1.3 ± 0.3	1.3 ± 0.3	1.0
LDL	2.7 ± 1.1	2.7 ± 0.9	1.0	3.0 ± 0.8	2.7 ± 0.8	<0.01^a
PT	10.7 ± 0.8	11.4 ± 0.9	<0.01^a	11.0 ± 0.7	11.0 ± 0.6	1.0
FBG	3.0 ± 0.4	2.6 ± 0.6	<0.01^a	2.9 ± 0.7	2.8 ± 0.6	0.24
ATPP	26.4 ± 2.7	27.4 ± 3.6	0.01^a	26.0 ± 2.9	26.3 ± 3.1	0.44
TT	18.3 ± 1.8	19.7 ± 16.3	0.38	18.2 ± 1.9	18.3 ± 1.9	0.68
LYM	2.0 ± 0.8	1.9 ± 0.7	0.27	2.2 ± 0.8	2.1 ± 1.4	0.46
MONO	0.4 ± 0.2	0.4 ± 0.2	1.0	0.4 ± 0.2	0.3 ± 0.3	0.67
PAG	26.9 ± 13.6	25.0 ± 10.0	0.18	27.7 ± 13.3	28.1 ± 6.1	0.71

Values expressed as mean ± SD or n (%).

Indicates a significant difference between the CAD group and the non-CAD group.

ATPP, activated partial thromboplastin time; BMI, body–mass index; CAD, coronary arterial disease; CK, creatine kinase; CKMB, creatine kinase mb; DBP, diastolic blood pressure; FBG, fibrinogen; HDL, high-density lipoprotein; LAD, left atrial diameter; LDL, low-density lipoprotein; LVEDD, left ventricular end diastolic diameter; LVEF, left ventricular ejection fraction; LYM, lymphocyte; MONO, monocyte; PAG, platelet aggregation; PT, prothrombin time; SBP, systolic blood pressure; SD, standard deviation; TC, triglycerides; TG, triglyceride; TT, thrombin.

Green tea consumption improved some CAD-related biomarkers

Out of the 280 male patients, 66.4% (186/280) routinely consumed green tea. The green tea, which most people drank was the “Longjin tea.” Males who regularly consumed green tea had higher PT ([12.2 ± 4.6] vs. [11.4 ± 3.3]) than men who did not consume green tea (p < 0.01). The females who regularly consumed green tea had higher HDL values than those who did not ([1.5 ± 0.4] vs. [1.2 ± 0.3]). They also had higher PT ([11.2 ± 2.3] vs. [10.1 ± 1.9]) (Table 2). The results suggested that green tea consumption improved CAD-related biomarkers, PT and HDL.

Table 2.

Characteristics of Male and Female Patients Who Did or Did Not Drink Green Tea

	Male			Female
	Green tea consumption (n = 186)	No green tea consumption (n = 94)	p	Green tea consumption (n = 93)	Nongreen tea consumption (n = 166)	p
Weight	67.1 ± 6.2	65.4 ± 7.7	0.06	59.2 ± 4.1	62.5 ± 9.6	<0.01^a
Age	60.0 ± 11.0	59.3 ± 13.2	0.65	64.9 ± 10.0	68.8 ± 9.3	<0.01^a
LVEF	64.6 ± 11.5	64.2 ± 10.7	0.77	65.4 ± 9.2	64.2 ± 11.5	0.36
LAD	34.6 ± 4.5	34.1 ± 5.1	0.41	34.5 ± 5.1	34.2 ± 4.3	0.63
LVEDD	49.7 ± 5.7	48.6 ± 6.0	0.13	46.8 ± 3.5	47.5 ± 4.4	0.16
TC	4.7 ± 2.6	4.3 ± 1.0	0.06	5.4 ± 0.9	5.2 ± 1.3	0.14
TG	3.1 ± 2.6	2.9 ± 1.2	0.38	2.1 ± 0.9	1.9 ± 1.2	0.13
HDL	1.7 ± 1.1	1.5 ± 1.1	0.14	1.5 ± 0.4	1.2 ± 0.3	<0.01^a
LDL	3.2 ± 0.7	3.2 ± 0.7	1.0	3.0 ± 0.7	3.0 ± 0.9	1.0
PT	12.2 ± 4.6	11.4 ± 3.3	<0.01^a	11.2 ± 2.3	10.1 ± 1.9	0.02^a
FBG	3.2 ± 0.8	3.1 ± 0.7	0.27	2.8 ± 0.5	2.9 ± 0.7	0.18
ATPP	28.8 ± 4.4	29.0 ± 4.0	0.70	26.6 ± 2.2	25.6 ± 3.1	<0.01^a
TT	36.4 ± 4.4	40.2 ± 36.6	0.30	18.1 ± 1.8	18.2 ± 2.0	0.68
LYM	3.0 ± 0.9	3.0 ± 0.8	1.0	2.0 ± 0.7	2.3 ± 0.8	0.42
PAG	30.3 ± 13.0	32.2 ± 10.8	0.19	26.0 ± 11.9	28.3 ± 13.8	0.16

Values expressed as mean ± SD or n (%).

Indicates a significant difference between the green tea consumption group and the group that did not drink green tea.

ATPP, activated partial thromboplastin time; FBG, fibrinogen; HDL, high-density lipoprotein; LAD, left atrial diameter; LDL, low-density lipoprotein; LVEDD, left ventricular end diastolic diameter; LVEF, left ventricular ejection fraction; LYM, lymphocyte; PAG, platelet aggregation; PT, prothrombin time; SD, standard deviation; TC, triglycerides; TG, triglyceride; TT, thrombin.

Green tea consumption did not reduce CAD risk in male participants

The results showed that those males who drank green tea did not have a reduced risk of CAD (odds ratio; OR = 1.58, 95% CI: 0.96–2.59, p > 0.05). Drinking green tea ≤1 cup/day (OR = 1.36, 95% CI: 0.82–2.26) or >1 cup/day (OR = 1.36, 95%CI: 0.77–2.41) did not reduce CAD risk. The frequency of 1–2 or >5 days/week did not influence CAD risk. The people with a frequency of 3–5 days/week (OR = 1.81, 95% CI: 1.02–3.22), a green tea consumption history of 10–20 years (OR = 3.22, 95% CI: 1.86–5.57), or >20 years (OR = 0.48, 95% CI: 0.24–0.93) were shown to have a reduced risk of CAD in males (Table 3).

Table 3.

Association Between Green Tea Consumption and Coronary Arterial Disease Risk in Male Patients

Green tea consumption	Male CAD (n = 173), n (%)	Male Non-CAD (n = 107), n (%)	Crude OR (95% CI)	p	Adjusted OR (95% CI)	p
Tea consumption
No	51 (29.5)	43 (40.2)	1	—	1	—
Yes	122 (70.5)	64 (59.8)	1.61 (0.97–2.67)	0.07	1.58 (0.96–2.59)	0.07
Amount of tea consumption per time (cups/day)
None	51 (29.5)	43 (40.2)	1	—	1	—
≤1	71 (41.0)	37 (34.6)	1.32 (0.80–2.17)	0.28	1.36 (0.82–2.26)	0.23
>1	49 (28.3)	25 (23.4)	1.30 (0.74–2.26)	0.36	1.36 (0.77–2.41)	0.29
Frequency of tea consumption (days/week)
None	51 (29.5)	43 (40.2)	1	—	1	—
1–2	18 (10.4)	12 (11.2)	0.92 (0.42–1.99)	0.83	0.95 (0.43–2.12)	0.90
3–5	54 (31.2)	23 (21.5)	1.66 (0.94–2.91)	0.08	1.81 (1.02–3.22)	0.04^a
>5	49 (28.3)	27 (25.2)	1.17 (0.68–2.02)	0.57	1.16 (0.67–2.02)	0.60
Duration of tea consumption (years)
None	51 (29.5)	43 (40.2)	1	—	1	—
0–10	18 (10.4)	14 (13.1)	0.77 (0.37–1.62)	0.49	0.79 (0.37–1.70)	0.54
10–20	83 (47.9)	26 (24.3)	2.87 (1.69–4.90)	<0.01	3.22 (1.86–5.57)	<0.01^a
>20	19 (11.0)	22 (20.6	0.48 (0.24–0.93)	0.03	0.48 (0.24–0.93)	0.03^a

Indicates a significant difference between the CAD group and the non-CAD group.

CAD, coronary arterial disease; CI, confidence interval; OR, odds ratio.

Green tea consumption reduced CAD risk in female participants

Women in the study who drank green tea had a reduced risk of CAD (OR = 0.13, 95% CI: 0.07–0.23, p < 0.01). The females who consumed ≤1 cup/day green tea had lower CAD risk (OR = 0.12, 95% CI: 0.07–0.23, p < 0.01). The frequency of 3–5 days/week (OR = 0.14, 95% CI: 0.07–0.29, p < 0.01) and >5 days/week (OR = 0.24, 95% CI: 0.08–0.69, p < 0.01) were both beneficial to preventing CAD. Those who had been drinking green tea for 0–10 years (OR = 0.11, 95% CI: 0.04–0.30) and 10–20 years (OR = 0.22, 95% CI: 0.11–0.46) had a reduced risk of CAD (Table 4).

Table 4.

Association Between Green Tea Consumption and Coronary Arterial Disease Risk in Female Patients

Green tea consumption	Female CAD (n = 94), n (%)	Female non-CAD (n = 165), n (%)	Crude OR (95% CI)	p	Adjusted OR (95% CI)	p
Green tea drink
No	66 (70.2)	100 (60.6)	1	—	1	—
Yes	28 (29.8)	65 (39.4)	0.65 (0.38–1.12)	0.12	0.13 (0.07–0.23)	<0.01^a
Amount of tea consumption (cups/day)
None	66 (70.2)	100 (60.6)	1	—	1	—
≤1	19 (20.4)	54 (32.7)	0.52 (0.29–0.95)	0.03	0.12 (0.07–0.23)	<0.01^a
>1	8 (8.6)	4 (2.4)	3.74 (1.10–12.79)	0.04	1.46 (0.37–5.78)	0.59
Frequency of tea consumption (days/week)
None	66 (70.2)	100 (60.6)	1	—	1	—
1–2	9 (9.6)	6 (3.6)	2.81 (0.97–8.15)	0.06	1.12 (0.36–3.43)	0.84
3–5	13 (13.8)	38 (23)	0.54 (0.27–1.07)	0.08	0.14 (0.07–0.29)	<0.01^a
>5	6 (6.4)	13 (7.9)	0.80 (0.29–2.17)	0.66	0.24 (0.08–0.69)	<0.01^a
Duration of tea consumption (years)
None	66 (70.2)	100 (60.6)	1	—	1	—
0–10	7 (7.4)	26 (15.8)	0.43 (0.18–1.03)	0.06	0.11 (0.04–0.30)	<0.01^a
10–20	13 (13.8)	30 (18.2)	0.72 (0.36–1.46)	0.37	0.22 (0.11–0.46)	<0.01^a
>20	6 (6.4)	9 (5.5)	0.31 (0.12–0.77)	0.01	0.37 (0.12–1.16)	0.09

Indicates a significant difference between the CAD group and the non-CAD group.

CAD, coronary arterial disease; CI, confidence interval; OR, odds ratio.

Gender differences of CAD and green tea consumption

There exists significant difference between male and female groups for CAD and green tea consumption (male: CAD, n = 173, 61.8%; female: CAD, n = 94, 36.3%; male: Green tea consumption, n = 186, 66.5%; female: Green tea consumption, n = 93, 35.9%). The results are shown in Table 5.

Table 5.

Gender Differences of Coronary Arterial Disease and Green Tea Consumption

	CAD	Green tea consumption
Male	173 (61.8%)	186 (66.5%)
Female	94 (36.3%)	93 (35.9%)
p	<0.001^a	<0.001^a

Indicates a significant difference between male and female.

CAD, coronary arterial disease.

Discussion

The pathogenesis of coronary heart disease is coronary atherosclerosis. The unstable atherosclerotic plaque of coronary atherosclerosis is closely related to the development of acute cardiovascular events in coronary heart disease. The unstable plaque rupture induces activation of fibrinolysis system and platelet adhesion promotes thrombosis. The process is closely related to PT, FBG, ATPP, and TT. The study suggests that the abovementioned related indicators in the coronary heart disease group were higher than those in the noncoronary heart disease group, which is consistent with the pathogenesis of coronary heart disease. TC, TG, and LDL, as major risk factors for coronary atherosclerosis, play an important role in the development of coronary atherosclerosis. HDL is a protective factor for coronary heart disease. LVEF, LAD, and LVEDD reflect the state of cardiac structure and function. LAD and LVEDD in patients with coronary heart disease could get larger as the heart structure gets larger, and LVEF may decrease. So the research indicators in this article are closely related to coronary heart disease.

Through the analysis of green tea consumption and CAD-related biomarkers, we found that green tea consumption might be beneficial for the reduction of coronary heart disease risk in female populations in Guangzhou, China (OR = 0.13, 95% CI: 0.07–0.23). Our results demonstrate that a small amount, high-frequency, and long-term green tea consumption was effective in coronary heart disease prevention for females in southern China. However, in the male study population, we did not find significant difference between the green tea consumption or nongreen tea consumption group (OR = 0.1.58, 95% CI: 0.96–2.59). We analyzed the characteristics of male and female patients who did or did not drink green tea and found that PT, ATPP, and HDL obviously increased, in female, whereas only PT increased in male. These different changes might cause the gender differences of green tea consumption and CAD.

PAG, blood coagulation, and thrombosis are the pathologic foundations of many cardiovascular–cerebrovascular diseases.¹⁴ Studies have shown that tea consumption could reduce blood coagulation,¹⁵ reduce fibrinogenesis,¹⁶ and promote the role of fibrinolysis in patients with coronary heart disease.^17
–19 The coagulation processes are a series of enzymatic actions, and the in vivo coagulation process can be divided into three stages: activation of prothrombin complex formation, activation of prothrombin by TT, and conversion of FBG into fibrin. Prothrombin is activated either by endogenous pathways or an exogenous pathway. The results of our research showed that the male and female participants who regularly consumed green tea had higher PT (male: 12.2 ± 4.6 vs. 11.4 ± 3.3; female: 11.2 ± 2.3 vs. 10.1 ± 1.9, p < 0.05) (Table 2). Prolonged PT suggested that green tea consumption could reduce blood coagulation, which results in decreased CAD risk. These results suggest that green tea catechins and (−)-epigallocatechin gallate could affect the antiplatelet activities in vitro and ex vivo. In addition, the latest study shows that the caffeine in tea could affect the PT in anticoagulant effects. So patients should be advised to limit the frequent use of caffeine-rich products, that is, tea and coffee during warfarin therapy.^20,21

HDL prevents the cardiovascular diseases mediated by LDL. By competing with components of the extracellular matrix, HDL suppresses the detention, aggregation, and oxidative denaturation of LDL on the blood vessel, which blocks the flow of a series of inflammatory reactions mainly involving macrophages. Then, HDL prevents MONOs from binding to the intima of blood vessel by downregulating chemotactic factors and cell adhesion factors. Additionally, HDL decreases the blood pressure because it promotes the release of nitric oxide from the vascular endothelium. As shown in Table 2, we found the female group who had the habit of drinking green tea had higher HDL ([1.5 ± 0.4] vs. [1.2 ± 0.3]), which is the protective lipid of coronary heart disease. Our findings in the present study suggested that green tea consumption raised the HDL levels, resulting in the suppression of cardiovascular diseases possibly. This could be related to the effects of tea polyphenol, which could increase the protective ingredient of lipids, and reduce the detrimental lipids.

Conclusions

Through the analysis of green tea consumption and CAD-related biomarkers, we concluded that a small amount, high-frequency green tea consumption was associated with a reduced risk of CAD in female populations in Guangzhou, China, and the association might be partly due to altered CAD-related biomarkers.

Study limitations

The limitations of this study are as follows. First, our study is a single-center study, which is only applicable to the association between tea and coronary heart disease in this sample population of Guangzhou, and cannot be projected to other populations. Second, the proportion of green tea consumption in the Guangzhou population may not represent the average proportion across China, so studies of increased scale are needed. Third, our research was retrospective, and prospective studies could better illustrate the association between tea consumption and CAD incidence. Therefore, prospective studies are needed and we suggest that future studies extend the follow-up period for individuals who drink green tea as it pertains to CAD incidence, to ascertain long-term outcomes.

Footnotes

Acknowledgments

This work was supported by the National Natural Science Foundation of China (81770494, 81760071); Natural Science Foundation of Guangdong Province (2015A030313026, 2017A030313877); Medical Research Foundation of Guangdong Province (B2013098); The Fundamental Research Funds for Colleges and Universities (3161033); National Clinical Key Specialty Construction Project of China (2013-544); Clinical Research Project of Department of Science and Technology of Guizhou province (2017-5405); and The Traditional Chinese Medicine Science and Technology Research in Guizhou Province (QZYY-2016-076).

Author Disclosure Statement

No competing financial interests exist.

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