Green Tea-FYI

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A prospective cohort study of more than 40,000 people in Japan has shown that

drinking green tea can significantly cut deaths from cardiovascular disease

(CVD) as well as all-cause mortality, particularly in women. There was no

beneficial effect of green tea consumption on cancer mortality, however.

http://www.medscape.com/viewarticle/544569?sssdmh=dm1.213424 & src=nldne

Shinichi Kuriyama, MD, from Tohuku University Graduate School of Medicine in

Miyagi, Japan, and colleagues, report their findings in the September 13 issue

of JAMA. Kuriyama told heartwire: " I think our study provides strong evidence

regarding the benefits of drinking green tea in humans on CVD, but not cancer,

with a large sample size. "

" The reason for the discrepancy between effects on CVD and on cancer deaths in

our study is uncertain. Substantial evidence from in vitro and animal studies

indicates that green tea preparations can inhibit both CVD and carcinogenic

processes. However, recent epidemiological studies have indicated that green tea

consumption is associated with reduced cardiovascular risk profiles but have

demonstrated almost null data regarding the association between green tea

consumption and cancer at various sites. Our results are almost consistent with

those of the recent epidemiologic studies. "

Green Tea Has Largest Effect on Stroke

Dr. Kuriyama and colleagues explain that almost all Japanese people consume

green tea as one of their favorite beverages. They designed their prospective

analysis to examine the association between green tea consumption and mortality

due to all causes, CVD, and cancer within a large population-based cohort study

of 40,530 people in Miyagi Prefecture in northeastern Japan.

For 11 years (follow-up rate for all-cause mortality, 86.1%), 4209 participants

died, and for up to 7 years, (follow-up rate for cause-specific mortality,

89.6%), 829 people died of CVD, and 1134 died of cancer.

Compared with participants who drank less than 1 cup of green tea per day, those

who consumed 5 or more cups had a risk for all-cause and CVD mortality that was

16% lower (during 11 years of follow-up) and 26% lower (during 7 years of

follow-up), respectively.

The inverse association with CVD mortality was stronger than that with all-cause

mortality, and among the types of CVD, the strongest inverse association was

seen for stroke mortality.

Table. Proportional Hazard Ratios (HRs) Among All Participants for 7-Year

Mortality Due to CVD by Green Tea Consumption in Japanese Adults*

Mortality Outcomes Green Tea Consumption, Cups/Day P for Trend

< 1 1 - 2 3 - 4 ? 5

CHD, No. of deaths 58 47 43 61

CHD, multivariate HR 1.00 1.04 0.90 0.86 0.34

Stroke, No. of deaths 145 99 102 126

Stroke, multivariate HR 1.00 0.84 0.78 0.63 <0.001

Cerebral infarction, No. of deaths 65 41 48 43

Cerebral infarction, multivariate HR 1.00 0.77 0.81 0.49 0.001

Cerebral hemorrhage, No. of deaths 34 30 33 40

Cerebral hemorrhage, multivariate HR 1.00 1.10 1.15 0.98 0.94

Subarachnoid hemorrhage, No. of deaths 21 13 12 26

Subarachnoid hemorrhage, multivariate HR 1.00 0.71 0.57 0.78 0.42

*CVD, indicates cardiovascular disease; and CHD, coronary heart disease.

Multivariate HR adjusted for age; sex; job status; years of education; body mass

index; physical activity, history of hypertension; diabetes; gastric ulcer;

smoking status; alcohol consumption; total energy intake per day; daily

consumption of rice, miso, soybean products, total meat, total fish, total

dairy, and total fruits and vegetables; and consumption of oolong tea, black

tea, and coffee.

Source: JAMA. 2006;296:1255-1265.

Green Tea Effect on CVD, All-Cause Mortality Stronger in Women

The inverse association between green tea consumption, CVD, and all-cause

mortality was stronger in women than in men (P = .08 for interaction with sex).

In women, the multivariate hazard ratios of CVD mortality across increasing

green tea consumption categories (cups/day) were 1.00, 0.84, 0.69, and 0.69,

respectively (P = .004 for trend).

" The reason for the discrepancy between men and women for the association of

green tea consumption and risk of all-cause and CVD mortality is uncertain, " say

the researchers.

" One possibility is residual confounding by cigarette smoking [as] men were more

likely to smoke, and the inverse associations between green tea consumption and

CVD mortality appeared to be more pronounced in participants who had never

smoked. These results suggest that higher rates of smoking may mask the

association of green tea consumption with CVD mortality among men. "

The authors add that the effect of green tea " appears to be a threshold effect

rather than a dose-response relationship, such that persons who consume at least

1 cup a day may receive some benefit. "

A number of biological mechanisms, including radical scavenging and antioxidant

properties, have been proposed for the beneficial effects of green tea. The

authors note that previous studies have suggested that green tea favorably

affects hypertension, low-density lipoprotein cholesterol levels, and

atherosclerosis.

However, " clinical trials are ultimately necessary to confirm the protective

effect of green tea on mortality, " the authors conclude.

JAMA. 2006;296:1255-1265.

The complete contents of Heartwire, a professional news service of WebMD, can be

found at www.theheart.org, a Web site for cardiovascular healthcare

professionals.

Learning Objectives for This Educational Activity

Upon completion of this activity, participants will be able to:

a.. Describe the effect of green tea consumption on all-cause mortality in men

and women.

b.. Compare the effect of green tea consumption on CVD vs cancer mortality.

Clinical Context

Tea is the most consumed beverage in the world aside from water and is generally

consumed as green, oolong, or black tea. Among teas, green tea polyphenols have

been extensively studied as preventive agents for CVD and cancer, which are the

leading causes of mortality worldwide. The mechanism of protection offered by

green tea is unclear, and the current authors propose that the radical

scavenging and antioxidant properties of polyphenols may be responsible.

Because green tea consumption is high in Japan, this study was conducted on

40,530 persons in a prefecture in Japan in which 80% of the population drinks

tea and more than half consume 3 or more cups a day. The purpose of the

prospective cohort study was to examine the effect of different amounts of daily

green tea consumption on all-cause, CVD, and cancer mortality.

Study Highlights

a.. The national insurance cohort, aged 40 to 79 years and living in one

public health catchment area, was delivered a self-administered questionnaire,

including a 40-item food frequency questionnaire (FFQ), for a 2-month period.

b.. Excluded were participants who died before the collection of insurance

withdrawal files; those with baseline history of cancer, stroke, or myocardial

infarction; and those with missing data on green tea consumption or improbable

daily caloric intakes.

c.. The frequency of recent daily consumption of 4 beverages (green, oolong,

black tea, and coffee), alcohol, and tobacco were elicited with demographic

data.

d.. In a validation of the FFQ, the rank coefficient for correlation between

the FFQ and daily food diary was 0.71 for men and 0.53 for women, and

reliability 1 year apart was 0.63 for men and 0.64 for women.

e.. Those who said they never drank green tea or drank occasionally were

collapsed into 1 category: less than 1 cup daily.

f.. The categories were less than 1 cup, 1 to 2 cups, 3 to 4 cups, and more

than 5 cups daily.

g.. Endpoints were all-cause mortality and cause-specific mortality.

h.. All-cause mortality was obtained monthly using national health insurance

withdrawal files, and follow-up continued for 11 years.

i.. Cause-specific mortality was obtained yearly by using death certificates

from the public health database coded by the International Statistical

Classification of Diseases, 10th Revision, and follow-up continued for 7 years.

j.. Participants who consumed more green tea were older; more likely to

consume soy, fish, vegetables, and other teas but less coffee; and more likely

to be unemployed and engaged in sports and to have a history of diabetes or

hypertension.

k.. For 11 years with 374,174 person-years, there were 4209 total deaths with

a follow-up rate of 86.1%.

l.. In men, the multivariate HR for all-cause mortality was 1.00 for less than

1 cup, 0.93 for 1 to 2, 0.95 for 3 to 4, and 0.88 for 5 or more cups daily (P =

..03 for trend).

m.. In women, the corresponding HRs were 1.00, 0.98, 0.82, and 0.77,

respectively (P < .001 for trend).

n.. There was no protection for all-cause mortality from consumption of black

or oolong tea.

o.. For 7 years of follow-up with 252,101 person-years, the total number of

deaths from CVD was 892 and 1134 from cancer, with a follow-up rate of 89.6%.

p.. Green tea consumption was inversely associated with mortality from CVD but

had no association with cancer mortality.

q.. As with all-cause mortality, the association was stronger for women than

for men.

r.. In women, those who drank 5 or more cups of green tea daily had a 31%

lower risk for CVD.

s.. In men, green tea consumption was significantly linked with reduced

mortality due to stroke, and in women, this protection was especially strong for

cerebral infarction.

t.. In women, those who drank more than 5 cups daily had a 42% and 62% lower

risk for death due to stroke and cerebral infarction, respectively.

u.. In both men and women, the multivariate HRs for gastric, lung, and

colorectal cancer was just above 1 but not statistically significant.

v.. Among current smokers, the HR for CVD for the categories of green tea

consumption were 1.00, 0.79, 0.81, and 0.86, respectively (P = .43 for trend,

not significant).

w.. Among never smokers, the corresponding HRs were 1.00, 0.85, 0.69, and

0.75, respectively (P = .03 for trend).

Pearls for Practice

a.. Consumption of 5 or more cups of green tea daily is associated with

reduction in all-cause mortality of 12% for men and 23% for women during 11

years of follow-up.

b.. Consumption of 5 or more cups of green tea daily is associated with

significant reduction in CVD mortality for men and women, particularly for

stroke and cerebral infarction, respectively, but has no association with cancer

mortality.

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Ortiz, RD

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