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IS COFFEE HARMFUL OR HEALTHFUL?Victoria J. Drake, Ph.D. |
Coffee is an infusion of ground, roasted coffee beans and is one of the most widely consumed beverages in the world. The drink contains more than a thousand different components, including carbohydrates, lipids, vitamins, minerals, alkaloids, phenols, and nitrogenous compounds. Overall, there is little evidence of health risks and some evidence of health benefits for adults consuming moderate amounts of coffee (3-4 cups/day, providing 300-400 mg/day of caffeine). Beneficial effects on mental state, along with coffee's aroma and flavor, are likely reasons why coffee is such a popular beverage. Because of the many variations in the manner in which coffee is prepared and consumed, it is difficult to interpret epidemiological studies.
Caffeine
Caffeine (1,3,7-trimethylxanthine) is an alkaloid that
occurs naturally in coffee beans. Caffeine consumption has
been linked to several positive effects on mental state,
including increased alertness, elevated mood, decreased
fatigue, and improved work performance. Moreover, two
prospective epidemiological studies have reported that
moderate coffee drinking significantly decreases the risk of
suicide. While the specific mechanisms for effects on health
and behavior are not established, it is known that caffeine
functions by blocking two adenosine receptors (A1 and A2A)
in the brain and consequently has an overall stimulatory
effect on the central nervous system.
Diterpenes
Boiled coffee beans also contain significant amounts of
the two diterpenes (a class of compounds with four isoprene
units), cafestol and kahweol. Some studies have associated
these compounds with increased levels of LDL (the "bad"
cholesterol) and total cholesterol. Filtered coffee, on the
other hand, contains very low levels of cafestol and kahweol
because they are mostly removed by the paper filter during
brewing. Indeed, filtered coffee consumption does not
appear to elevate serum cholesterol concentrations.
Chlorogenic acid
Coffee naturally contains polyphenolic compounds called
chlorogenic acids, which are esters of quinic and cinnamic
acids. The most prevalent individual chlorogenic acid is
5-O-caffeoylquinic acid but often simply called chlorogenic
acid. Chlorogenic acid has been shown to exhibit antioxidant
activity in vitro; however, the extent of antioxidant activity
in vivo is unclear.
Other components
Coffee contains a number of other compounds that could
potentially affect human health, such as various micronutrients
like magnesium, potassium, niacin, and vitamin E.
Additionally, coffee is a dietary source of several lignans
(phytoestrogens) that may alter glucose metabolism as well as
trigonelline (N-methylnicotinic acid), a phytochemical that
has been shown to have a hypoglycemic effect in diabetic rats.
Prevention of type 2 diabetes mellitus
Several prospective epidemiological studies have consistently
reported that habitual intake of caffeinated coffee lowers
the risk of type 2 diabetes mellitus (DM). Interestingly,
decaffeinated coffee was recently reported to decrease type
2 DM risk and also to positively alter glucose metabolism,
suggesting that non-caffeine components in coffee may offer
protection against the disease. More prospective research is
needed to determine whether consumption of decaffeinated
coffee also lowers type 2 DM risk. Additionally, mechanistic
studies investigating the effects of individual constituents of
coffee will provide insight into the observed anti-diabetic effect.
Prevention of Parkinson's disease
To date, results of most case-control and prospective
cohort studies suggest that routine coffee and caffeine
consumption decreases the risk of Parkinson's disease in men
but not in women. However, one study in 77,713 women
participating in the Nurses' Health Study found that coffee
consumption decreased Parkinson's disease risk in women
who had never used postmenopausal estrogen, and high
coffee intakes actually increased risk of Parkinson's disease in
women using estrogen replacement therapy. More prospective
research is necessary to determine whether coffee or caffeine
intake alters Parkinson's disease risk and whether
postmenopausal use of estrogen modifies the association.
Prevention of liver diseases
Some studies have found that coffee intake decreases
risk of liver diseases, including cirrhosis and hepatocellular
carcinoma. Caffeine and chlorogenic acid have
been reported to inhibit hepatic carcinogenesis in
animals, yet more mechanistic studies are necessary
to determine the exact relationship.
Prevention of colorectal cancer
Case-control studies have generally found that coffee
drinking lowers risk of colorectal cancer; however,
prospective cohort studies have largely reported no effect. It is
generally recognized that prospective studies in which nutrient
intake is measured in healthy people and disease outcome is
determined later have a stronger experimental design than
case-control studies, which rely on comparing subjects
diagnosed with disease to other subjects without the disease.
Thus, more prospective research on coffee consumption
and colorectal cancer is warranted to make any definitive
conclusions about the association.
Effects on mental state
Coffee intake has been shown to improve overall mood
and mental performance; however, these effects are highly
dependent on caffeine dose and habituation. Negative effects,
such as increased anxiety and sleep disturbances, have also
been reported with coffee intake, especially in non-habitual
consumers.
Cardiovascular diseases
Case-control and prospective epidemiological studies on
the effects of coffee intake on cardiovascular disease report
conflicting results. Therefore, it is not clear whether coffee
drinking increases risk for various cardiovascular diseases,
including myocardial infarction, stroke, and coronary heart
disease. However, studies have associated consumption of
caffeinated coffee with increases in blood pressure and
plasma homocysteine levels, two independent risk factors
for cardiovascular diseases.
It is well-established that acute caffeine administration increases blood pressure, but recent studies suggest that chronic consumption of caffeinated coffee may not raise blood pressure, presumably because tolerance to caffeine develops.
Cancer
Most studies to date report that moderate coffee drinking
does not elevate risk for pancreatic, lung, bladder, or
renal cancer.
Osteoporosis and bone fracture
Studies investigating the effect of coffee or caffeine
consumption on osteoporosis and bone fracture risk have
reported mixed results. While large-scale, prospective studies
are needed to determine whether coffee or caffeine intake
alters osteoporosis or fracture risk, currently available data
suggest that limiting coffee consumption to three cups daily
(300 mg/d of caffeine) and ensuring adequate calcium and
vitamin D nutrition may help prevent any adverse effects
on bone status.
Caffeine and pregnancy complications
Some studies have reported that high intakes of caffeine
during pregnancy are associated with adverse effects,
including spontaneous abortion, retarded fetal growth,
and low birth weight. Studies suggest that caffeine does
not influence preterm delivery or birth defects. Currently,
it is recommended that pregnant women limit daily caffeine
intake to 300 mg (about three cups of coffee).
Special risk groups
In addition to pregnant women, older adults may
be more vulnerable to any adverse effects of caffeine,
including acute increases in blood pressure and any
negative effects on bone status. Caffeine distributes
primarily to lean body mass instead of adipose tissue,
and older adults have lower lean mass to adipose ratios
than younger adults; thus, the caffeine dose may be more
concentrated in older individuals. Another group that may
be susceptible to the negative effects of caffeine is children,
but studies in this age group are limited, and additionally,
most studies have focused on behavioral endpoints.
High caffeine intakes in children have been linked to
increased anxiety and sleep disturbances.
Please see the Linus Pauling Institute's Micronutrient Information Center for more information on coffee and health.
Last updated December 2007
