From Nature Clinical Practice Gastroenterology & Hepatology
Is Coffee or Tea Good for Your Liver?
Posted 10/02/2006
W Ray Kim
Synopsis
Background
It has been postulated that the consumption of coffee and tea is associated
with reduced liver disease; however, this relationship has not been assessed
in the US on a population-wide basis.
Objectives
To investigate the association between chronic liver disease (CLD) and
consumption of coffee and tea.
Design and Intervention
This study employed data from the US National Health and Nutrition
Examination Survey (NHANES) 1971-1975 on coffee, tea, and alcohol
consumption, and also that from the NHANES Epidemiologic Follow-Up Study.
Data from a separate analysis (1982-1984) assessing more detailed drinking
habits of some participants from the NHANES were also included. In both
analyses, daily consumption was categorized as <1 cup, 1-2 cups, or >2 cups.
Exclusion criteria included lack of data on coffee and tea consumption,
jaundice, hepatomegaly, splenomegaly, and serum albumin >30 g/l. BMI was
calculated for all participants and laboratory tests, including transferrin
saturation, serum iron, and iron-binding capacity, were performed.
Participants were followed up until 1992 or 1993; follow-up included
interview and examination of death certificate or hospital records. CLD was
determined by death certificate or hospital discharge record. A number of
statistical tests were performed on the available data.
Outcome Measures
The main outcome measures were coffee and tea consumption and the incidence
of CLD.
Results
In total, data from 9,849 NHANES participants (mean follow-up 19 years
[range 0.2-22.1 years]) and 9,650 participants from the separate analysis
were included. Mean daily intake of coffee and tea in the NHANES group was 2
cups (range 0-16 cups), and the mean daily consumption (in cups) for each
category was 0.2 for <1 cup, 1.5 for 1-2 cups, and 4.0 for >2 cups. The risk
of death or hospitalization from CLD was 1.4% at 20-year follow-up. The
unadjusted risk of CLD at 20 years was 1.8% (hazard ratio [HR] 1.0) for
those who drank <1 cup per day, 1.6% (HR 0.84, 95% CI 0.52-1.40) for those
who drank 1-2 cups per day, and 1.1% (HR 0.46, 95% CI 0.26-0.80) for those
who drank >2 cups per day (P = 0.002). The incidence of CLD was higher in
participants with a BMI ¡Ý30 (1.8%; HR 1.5, 95% CI 0.87-2.50) than those
with a BMI of 25 to <30 (1.6%; HR 1.5, 95% CI 0.99-2.30) or <25 (1.2%; HR
1.0) Multivariate analysis revealed that drinking >2 cups of coffee per day
reduced the risk of CLD by more than 50% compared to those who drank <1 cup
per day (HR 0.43, 95% CI 0.24-0.75 vs HR 1.0; P = 0.003). The incidence of
CLD in high-risk individuals (such as those with diabetes or a high alcohol
consumption) drinking >2 cups per day was less than in those drinking ¡Ü2
cups per day (1.1%; HR 0.40, 95% CI 0.23-0.68 vs 2.3%; HR 1.0; NS).
Conclusion
The consumption of coffee and tea is associated with a reduced risk of CLD.
Commentary
Is coffee or tea good for your liver? The study by Ruhl and Everhart seems
to indicate that drinking coffee or tea does decrease the risk of clinically
significant CLD. This work extends their previous observation that coffee
and caffeine consumption is associated with lower serum alanine
aminotransferase (ALT) levels.[1] In this earlier study, which included
subjects who participated in the third NHANES, and who were deemed at high
risk of liver disease, coffee and caffeine intake was inversely correlated
with serum ALT levels.
The current study cleverly uses longitudinal data made available through the
NHANES Epidemiologic Follow-up Study. The main strength of this analysis is
that the study was based on prospective collection of exposure history
(coffee or tea consumption) and clinical outcome (hospitalization or death
due to CLD) in a large population-based sample (NHANES-I). Methodologically,
however, this study was limited for a number of reasons. Firstly, a
relatively large proportion (25%) of subjects were excluded from the
analysis because of a lack of data on coffee or tea consumption; secondly,
ascertainment of liver disease was based on hospital discharge records and
death certificates, as opposed to verifiable clinical records; and thirdly,
there was a lack of detail regarding the amount and type of beverage
consumed. Weighing up these strengths and limitations, however, the reader
becomes intrigued (if not reasonably convinced) that coffee or tea
consumption might, indeed, be good for the liver.
Caution must be exercised, however, before physicians begin to advise
patients with liver disease to consume more tea or coffee. Although these
observational data show a consistent association between coffee or tea
consumption and CLD, it is premature to conclude a causal relationship
between the two (i.e that these beverages reduce the risk of liver disease).
Firstly, no known ingredients of coffee or tea have been linked with a
protective effect in the pathogenesis of CLD. Caffeine might not be
responsible, as caffeine-containing beverages other than coffee did not show
any benefit in a study by Corrao et al.[2] Despite the recent interest in
the antioxidant and other potentially beneficial properties of catechins in
tea, a protective effect against CLD remains to be determined.[3]
Secondly, it is possible that the association revealed in this study might
have been confounded with other dietary or behavioral factors that are
indeed responsible for the reduced risk of CLD. For example, coffee or tea
consumption was inversely associated with BMI. It could be that the
consumption of these beverages is associated with healthier dietary
practices, which might reduce the risk of the metabolic syndrome¡ªitself
associated with nonalcoholic fatty liver disease, the most common cause of
CLD in the US. Similarly, consumption of coffee or tea might be inversely
correlated with heavy alcohol consumption. The lack of a consistent pattern
between coffee or tea consumption and alcohol intake in the Ruhl and
Everhart study might be attributable to the fact that all levels of alcohol
consumption >2 drinks per day were lumped together; patients with alcoholic
liver disease who consumed >2 alcoholic drinks per day could not be
separately analyzed. Although some of these questions were addressed in
European studies, differences in culture and liver disease epidemiology make
it difficult to directly extrapolate those results.[2,4]
In summary, Ruhl and Everhart provide as strong evidence as observational
data possibly can for an inverse relationship between coffee or tea intake
and CLD. Before coffee or tea can be 'prescribed' in patients with liver
disease, however, interventional data are strongly warranted.
Practice Point
There might be an inverse relationship between tea, coffee, or caffeine
intake and liver disease; however, further data are needed before tea or
coffee can be adopted as a treatment in patients with chronic liver disease.
Acknowledgements
The synopsis was written by Rachel Jones, Associate Editor, Nature Clinical
Practice.
Reprint Address
Gastroenterology and Hepatology, Plummer 6 Mayo Clinic College of Medicine
200 First Street, SW Rochester, MN 55905 USA. Email: [email protected]
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发表于 2006-10-16 00:44
